On Wednesday 08 August 2007 16:47, Matthew Toseland wrote:
> On Wednesday 08 August 2007 16:45, Matthew Toseland wrote:
> > On Wednesday 08 August 2007 16:42, Matthew Toseland wrote:
> > > On Wednesday 08 August 2007 16:26, Matthew Toseland wrote:
> > > > On Wednesday 08 August 2007 16:25, Matthew Toseland wrote:
> > > > > On Wednesday 08 August 2007 16:23, Matthew Toseland wrote:
> > > > > > On Wednesday 08 August 2007 16:22, Matthew Toseland wrote:
> > > > > > > On Wednesday 08 August 2007 16:20, Matthew Toseland wrote:
> > > > > > > > On Wednesday 08 August 2007 16:19, Matthew Toseland wrote:
> > > > > > > > > On Wednesday 08 August 2007 16:17, Matthew Toseland wrote:
> > > > > > > > > > On Wednesday 08 August 2007 16:05, Matthew Toseland wrote:
> > > > > > > > > > > Continued at end to minimise confusion!
> > > > > > > > > > >
> > > > > > > > > > > On Wednesday 08 August 2007 15:59, Matthew Toseland
wrote:
> > > > > > > > > > > > Unfortunately this thread is rather rambling, it
> > > > > > > > > > > > includes lots of discussion on token passing as well
> > > > > > > > > > > > as the original premise.
> > > > > > > > > > > >
> > > > > > > > > > > > ----- Anonymous at o9_0DTuZniSf_+oDmRsonByWxsI -----
> > > > > > > > > > > > 2007.04.25 - 20:18:36GMT -----
> > > > > > > > > > > >
> > > > > > > > > > > > I made some measurements on how freenet node behaves
> > > > > > > > > > > > if bandwidth limit is set low: 10KBps and downto
> > > > > > > > > > > > 6KBps (specificially, input bandwidth limit; output
> > > > > > > > > > > > bandwidth limit was set to at least 15KBps but as
> > > > > > > > > > > > expected factually used output bandwidth is
> > > > > > > > > > > > comparable (just slightly above) with factually used
> > > > > > > > > > > > input bandwidth). The node itself was running frost
> > > > > > > > > > > > but no
> > > > > > > > > > > > uploads/downloads, so absolute majority of network
> > > > > > > > > > > > traffic was forwarded CHK/SSK
> > > > > > > > > > > > requests/inserts.
> > > > > > > > > > > >
> > > > > > > > > > > > Results are interesting enough: CHK traffic becomes
> > > > > > > > > > > > as low as 5% (in packets) of CHK+SSK, while at least
> > > > > > > > > > > > 92% of SSK requests were not satisfied for assorted
> > > > > > > > > > > > failures (plus quite some more certainly resulted in
> > > > > > > > > > > > NotFound response due to missing the key in whole
> > > > > > > > > > > > network, but I don't have the number). This makes low
> > > > > > > > > > > > traffic node working highly inefficient and
> > > > > > > > > > > > improportionally slow; this also slows down its peers
> > > > > > > > > > > > with all the extra reject traffic. Worse, input
> > > > > > > > > > > > bandwidth sometimes goes over set limit, suggesting
> > > > > > > > > > > > that on hardware 33600/56000 Kbps modem and even ISDN
> > > > > > > > > > > > things will just get worse due to increased delays.
> > > > > > > > > > > >
> > > > > > > > > > > > Another thing to note: low bandwidth node (LBN)
> > > > > > > > > > > > almost exclusively reject requests with "input
> > > > > > > > > > > > bandwidth liability" reason, and extremely rarely
> > > > > > > > > > > > other reasons.
> > > > > > > > > > > >
> > > > > > > > > > > > Speculating a bit, the same picture will likely be
> > > > > > > > > > > > observed for peers of fast node (1Mbps or more) with
> > > > > > > > > > > > many peers having typical home connection of 256Kbps
> > > > > > > > > > > > or less.
> > > > > > > > > > > >
> > > > > > > > > > > > Not sure if simulations ever showed anything like
> > > > > > > > > > > > this, but contributing to network mostly SSK service
> > > > > > > > > > > > (and absolute majority of SSK requests fail!) is
> > > > > > > > > > > > rather useless: optimally working network is supposed
> > > > > > > > > > > > to transfer at least one CHK block for each SSK key,
> > > > > > > > > > > > and typically much much more (single 10MB file
> > > > > > > > > > > > consists of 481 CHK blocks!), and even if you found
> > > > > > > > > > > > SSK but not CHK the SSK points to, then you failed to
> > > > > > > > > > > > find information you requested.
> > > > > > > > > > > >
> > > > > > > > > > > > OK to make the long story short[er], at the end of
> > > > > > > > > > > > this message you will find a small patch that
> > > > > > > > > > > > noticably improves LBN situation. Idea is to reserve
> > > > > > > > > > > > some bandwidth for CHK transfers (and SSK inserts, as
> > > > > > > > > > > > those are too rare to penalize, and more valuable
> > > > > > > > > > > > than requests). The line directly before the inserted
> > > > > > > > > > > > one implicitly penalizes CHK transfers (as much
> > > > > > > > > > > > smaller SSK requests tend to rereserve bandwidth the
> > > > > > > > > > > > next moment it got released after CHK transfer
> > > > > > > > > > > > finish, while much larger CHK requests do not have
> > > > > > > > > > > > such good chance), so bandwidth should be reserved
> > > > > > > > > > > > for 2 CHKs at least (and tests show that's enough to
> > > > > > > > > > > > make a difference).
> > > > > > > > > > > >
> > > > > > > > > > > > Another thing I tried was increasing the 90 seconds
> > > > > > > > > > > > period up to 120. That had some (no numbers here;
> > > > > > > > > > > > just "noticeable but small") positive effect on
> > > > > > > > > > > > making traffic smoother and staying closer to set
> > > > > > > > > > > > limit, without jumping up and down too much. Where
> > > > > > > > > > > > the 90 seconds number came from anyway, and how
> > > > > > > > > > > > dangerous 120 could be?
> > > > > > > > > > > >
> > > > > > > > > > > > Some pros observed and/or thought out during tests of
> > > > > > > > > > > > the patch: - I observe increase of output payload by
> > > > > > > > > > > > approx. 15% (of total traffic), making LBN more
> > > > > > > > > > > > useful for its peers. - the change is negligibly
> > > > > > > > > > > > small for faster nodes so should not break anything
> > > > > > > > > > > > globally. - entire network SSK flood traffic will be
> > > > > > > > > > > > toned down a little bit (at temporary overloaded
> > > > > > > > > > > > nodes only), additionally simplifying life for LBNs:
> > > > > > > > > > > > after all, requesting the same SSK every 15 seconds
> > > > > > > > > > > > for 35 hours, total 8100 times (factual numbers from
> > > > > > > > > > > > one of the test before this patch applied; there are
> > > > > > > > > > > > over 60 other SSKs that were requested more than 1000
> > > > > > > > > > > > times during the same period) is just way too much,
> > > > > > > > > > > > SSKs are not inserted into network THAT fast. [does
> > > > > > > > > > > > it worth to remember recently seen SSK requests, and
> > > > > > > > > > > > do not forward them if same request was already
> > > > > > > > > > > > forwarded within last 10 minutes and resulted in
> > > > > > > > > > > > DNF/RNF? Table of recently requested SSKs that are
> > > > > > > > > > > > closest to the node location should not be too big?].
> > > > > > > > > > > >
> > > > > > > > > > > > And contras:
> > > > > > > > > > > > - in exceptional conditions (specificially, with less
> > > > > > > > > > > > than 2 incoming CHK requests per 90 seconds;
> > > > > > > > > > > > factually I observe 2-7 CHK requests per seconds,
> > > > > > > > > > > > that's 180-630 per 90 seconds) notwithstanding node
> > > > > > > > > > > > bandwidth speed, up to 800 Bps might end being
> > > > > > > > > > > > unused. For high bandwidth node that's just way too
> > > > > > > > > > > > small to notice, for LBN that's still acceptable (10%
> > > > > > > > > > > > of 56Kbps) and will decrease roundtrip delays a bit
> > > > > > > > > > > > which is always a good thing for so slow links.
> > > > > > > > > > > >
> > > > > > > > > > > > Other notes:
> > > > > > > > > > > > - distribution of location closeness/number of SSK
> > > > > > > > > > > > requests is very nice: only SSK requests with
> > > > > > > > > > > > location very close to node location get repeated
> > > > > > > > > > > > frequently; farther SSK location is, less requests
> > > > > > > > > > > > the node sees, with those SSKs seen only once or two
> > > > > > > > > > > > times per 1-2 days period are distributed evenly
> > > > > > > > > > > > among location space. This suggests that routing is
> > > > > > > > > > > > working fine. - As far as I understand, if input
> > > > > > > > > > > > bandwidth limit/liability exceeded (but a packet
> > > > > > > > > > > > already received anyway), CHK/SSK request gets
> > > > > > > > > > > > instantly rejected (thus throwing out received bytes
> > > > > > > > > > > > while input bandwidth has no spare volume!); only
> > > > > > > > > > > > otherwise node checks if the requested key exists in
> > > > > > > > > > > > the storage. Heh? This feels like a serious bug
> > > > > > > > > > > > hurting overall network performance: better query
> > > > > > > > > > > > storage and hopefully send back result (or still
> > > > > > > > > > > > reject if the key not found locally) rather than wait
> > > > > > > > > > > > for retry request to waste more input bandwidth. At
> > > > > > > > > > > > least for SSK reject and reply are comparable in
> > > > > > > > > > > > output bandwidth usage, so worth a little delay in
> > > > > > > > > > > > response. Or do I miss something?
> > > > > > > > > > > >
> > > > > > > > > > > > ===
> > > > > > > > > > > > diff --git a/freenet/src/freenet/node/NodeStats.java
> > > > > > > > > > > > b/freenet/src/freenet/node/NodeStats.java
> > > > > > > > > > > > index 3b091b4..fb9f8b9 100644
> > > > > > > > > > > > --- a/freenet/src/freenet/node/NodeStats.java
> > > > > > > > > > > > +++ b/freenet/src/freenet/node/NodeStats.java
> > > > > > > > > > > > @@ -414,6 +414,7 @@ public class NodeStats implements
> > > > > > > > > > > > Persistable {
> > > > > > > > > > > >
> > > > > > > > > > > > successfulChkInsertBytesReceivedAverage.currentValue(
> > > > > > > > > > > >) * node.getNumCHKInserts() +
> > > > > > > > > > > >
> > > > > > > > > > > > successfulSskInsertBytesReceivedAverage.currentValue(
> > > > > > > > > > > >) * node.getNumSSKInserts();
> > > > > > > > > > > > bandwidthLiabilityInput +=
> > > > > > > > > > > > getSuccessfulBytes(isSSK, isInsert,
> > > > > > > > > > > > true).currentValue(); + if (isSSK &&
> > > > > > > > > > > > !isInsert)
> > > > > > > > > > > > bandwidthLiabilityInput+=successfulChkFetchBytesRecei
> > > > > > > > > > > >ve dA ve ra ge .c ur re nt Va lu
> > > > > > > > > > > > e()+successfulChkInsertBytesReceivedAverage.currentVa
> > > > > > > > > > > >lu e( ); // slightly penalize SSK requests by
> > > > > > > > > > > > reserving bandwidth for 2 additional CHK transfers
> > > > > > > > > > > > (or SSK inserts if any) double
> > > > > > > > > > > > bandwidthAvailableInput =
> > > > > > > > > > > > node.getInputBandwidthLimit() * 90; // 90 seconds at
> > > > > > > > > > > > full power
> > > > > > > > > > > > if(bandwidthLiabilityInput >
> > > > > > > > > > > > bandwidthAvailableInput) { ===
> > > > > > > > > > > >
> > > > > > > > > > > > ----- toad at zceUWxlSaHLmvEMnbr4RHnVfehA -----
> > > > > > > > > > > > 2007.04.26 - 16:56:59GMT -----
> > > > > > > > > > > >
> > > > > > > > > > > > Most SSK requests fail. They DNF. The reason for this
> > > > > > > > > > > > is most SSK requests are polling for data that has
> > > > > > > > > > > > not yet been inserted.
> > > > > > > > > > > >
> > > > > > > > > > > > Bandwidth liability is usually the main reason for
> > > > > > > > > > > > rejection. If we reach most of the other reasons,
> > > > > > > > > > > > there is a problem - usually a cyclical problem. The
> > > > > > > > > > > > main reason for it is to ensure that we don't accept
> > > > > > > > > > > > so many requests that some of them needlessly timeout
> > > > > > > > > > > > even though they succeeded. The timeout is 120
> > > > > > > > > > > > seconds, so we need the actual transfer to take less
> > > > > > > > > > > > than this; on a request, 30 seconds seems a
> > > > > > > > > > > > reasonable upper bound for the search time. We don't
> > > > > > > > > > > > throw out many bytes when we reject a request/insert
> > > > > > > > > > > > because the bulk of it hasn't been sent yet, except
> > > > > > > > > > > > with SSKs where typically a little under half of the
> > > > > > > > > > > > total bytes will have been moved. Ideally we wouldn't
> > > > > > > > > > > > send requests until we have a good idea that they
> > > > > > > > > > > > will be accepted, but token passing load balancing is
> > > > > > > > > > > > a long way off, not likely to happen for 0.7.0.
> > > > > > > > > > > >
> > > > > > > > > > > > We cannot control input bandwidth usage precisely.
> > > > > > > > > > > >
> > > > > > > > > > > > Any more info on SSK flooding? Is it simply Frost?
> > > > > > > > > > > >
> > > > > > > > > > > > We can add a failure table, we had one before,
> > > > > > > > > > > > however a failure table which results in actually
> > > > > > > > > > > > blocking keys can be extremely dangerous; what I had
> > > > > > > > > > > > envisaged was "per node failure tables" i.e. reroute
> > > > > > > > > > > > requests which have recently failed to a different
> > > > > > > > > > > > node since we know it isn't where it's supposed to
> > > > > > > > > > > > be.
> > > > > > > > > > > >
> > > > > > > > > > > > On what do you base the assertion about key
> > > > > > > > > > > > closeness? It would be nice to have a histogram or
> > > > > > > > > > > > circle on the stats pages showing recent keys on the
> > > > > > > > > > > > keyspace - can you write a patch?
> > > > > > > > > > > >
> > > > > > > > > > > > As far as your patch goes, surely rejecting more SSK
> > > > > > > > > > > > requests would be counterproductive as it wastes
> > > > > > > > > > > > bandwidth? Shouldn't a slow node accept those
> > > > > > > > > > > > requests it's likely to be able to handle?
> > > > > > > > > > > >
> > > > > > > > > > > > I can see an argument that we shouldn't prefer SSKs,
> > > > > > > > > > > > and that on slow nodes we do prefer SSKs... I'm not
> > > > > > > > > > > > sure the above is the right way to deal with it
> > > > > > > > > > > > though. The effect of the patch would be to never
> > > > > > > > > > > > accept any SSKs unless we have plenty of spare
> > > > > > > > > > > > bandwidth, correct?
> > > > > > > > > > > >
> > > > > > > > > > > > ----- Anonymous at o9_0DTuZniSf_+oDmRsonByWxsI -----
> > > > > > > > > > > > 2007.04.26 - 18:41:32GMT -----
> > > > > > > > > > > >
> > > > > > > > > > > > > Ideally we wouldn't send requests until we have a
> > > > > > > > > > > > > good idea that they will
> > > > > > > > > > > >
> > > > > > > > > > > > be accepted, but token passing load balancing is a
> > > > > > > > > > > > long way off, not likely to happen for 0.7.0.
> > > > > > > > > > > >
> > > > > > > > > > > > Well, even current algorithm implementation has
> > > > > > > > > > > > certain room for improvement. Here is the typical
> > > > > > > > > > > > numbers I observe:
> > > > > > > > > > > >
> > > > > > > > > > > > ===
> > > > > > > > > > > > unclaimedFIFO Message Counts
> > > > > > > > > > > > * FNPRejectOverload: 89 (45.2%)
> > > > > > > > > > > > * FNPInsertTransfersCompleted: 59 (29.9%)
> > > > > > > > > > > > * FNPDataNotFound: 15 (7.6%)
> > > > > > > > > > > > * packetTransmit: 12 (6.1%)
> > > > > > > > > > > > * FNPRejectLoop: 7 (3.6%)
> > > > > > > > > > > > * FNPAccepted: 6 (3.0%)
> > > > > > > > > > > > * FNPSwapRejected: 4 (2.0%)
> > > > > > > > > > > > * FNPDataInsertRejected: 4 (2.0%)
> > > > > > > > > > > > * FNPRouteNotFound: 1 (0.5%)
> > > > > > > > > > > > * Unclaimed Messages Considered: 197
> > > > > > > > > > > > ===
> > > > > > > > > > > >
> > > > > > > > > > > > FNPRejectOverload always stays at top sometimes with
> > > > > > > > > > > > hundreds messages (for the last hour before unclaimed
> > > > > > > > > > > > messages expire, that's alot), and so indicates that
> > > > > > > > > > > > there is some bug (or bugs) with bandwidth limiting
> > > > > > > > > > > > obeying.
> > > > > > > > > > > >
> > > > > > > > > > > > > Any more info on SSK flooding? Is it simply Frost?
> > > > > > > > > > > >
> > > > > > > > > > > > Not local frost for sure, it generates just several
> > > > > > > > > > > > SSK simultaneous requests (by default max 8: 6 for
> > > > > > > > > > > > boards plus 2 for filesharing, AFAIR; practically 2-4
> > > > > > > > > > > > simutaneous requests most of the time). Other 100 SSK
> > > > > > > > > > > > requests (without proposed patch) are forwarded ones.
> > > > > > > > > > > >
> > > > > > > > > > > > >We can add a failure table, we had one before,
> > > > > > > > > > > > > however a failure table which
> > > > > > > > > > > >
> > > > > > > > > > > > results in actually blocking keys can be extremely
> > > > > > > > > > > > dangerous;
> > > > > > > > > > > >
> > > > > > > > > > > > Is it, having timeout of max few minutes (i.e. at
> > > > > > > > > > > > least few times less than SSK propagation time
> > > > > > > > > > > > visible with frost messages)? Is it more dangerous
> > > > > > > > > > > > than current wastage of bandwith for same SSK key
> > > > > > > > > > > > requests several times per minute? Had some
> > > > > > > > > > > > simulations been done on that in the past?
> > > > > > > > > > > >
> > > > > > > > > > > > BTW, isn't the observed very low store hit rate
> > > > > > > > > > > > results from prioritising the likely-to-fail SSKs?
> > > > > > > > > > > >
> > > > > > > > > > > > BTW2 the failure table could also act as a targetted
> > > > > > > > > > > > content propagation mechanism: if a node sees SSK
> > > > > > > > > > > > insert for a temporary blacklisted (non-existing)
> > > > > > > > > > > > SSK, then forwarding the insert (more likely insert
> > > > > > > > > > > > copy, for security reasons and routing sake) to the
> > > > > > > > > > > > original requestor should speed up propagaton of new
> > > > > > > > > > > > SSKs toward the nodes that already anticipate/await
> > > > > > > > > > > > for them.
> > > > > > > > > > > >
> > > > > > > > > > > > >what I had envisaged was "per node failure tables"
> > > > > > > > > > > > > i.e. reroute requests
> > > > > > > > > > > >
> > > > > > > > > > > > which have recently failed to a different node since
> > > > > > > > > > > > we know it isn't where it's supposed to be.
> > > > > > > > > > > >
> > > > > > > > > > > > At a glance, very nice idea. But LBNs typically
> > > > > > > > > > > > answer with reject, not DFN... even with current
> > > > > > > > > > > > code. Probably such rerouting will even further
> > > > > > > > > > > > increase SSK traffic toward LBNs, and get sharply
> > > > > > > > > > > > increased volume of SSK rejects as result. Hmm, some
> > > > > > > > > > > > testing/simulation seems really needed here.
> > > > > > > > > > > >
> > > > > > > > > > > > >On what do you base the assertion about key
> > > > > > > > > > > > > closeness? It would be nice to
> > > > > > > > > > > >
> > > > > > > > > > > > have a histogram or circle on the stats pages showing
> > > > > > > > > > > > recent keys on the keyspace - can you write a patch?
> > > > > > > > > > > >
> > > > > > > > > > > > Mmmm... in fact I just added custom logging, then a
> > > > > > > > > > > > wild combination of grep/sed/sort/uniq to analyze the
> > > > > > > > > > > > logs. But let me think, maybe visualizing a couple of
> > > > > > > > > > > > stats files I operate with will be rather trivial...
> > > > > > > > > > > >
> > > > > > > > > > > > But I would rather stay away from stats page graphics
> > > > > > > > > > > > at this time, as the stats files I operate
> > > > > > > > > > > > (filtered+sorted+uniqued) with are rather large,
> > > > > > > > > > > > 20-50Mb each - too much memory for the toy. Unless
> > > > > > > > > > > > your 'recent' means just 10-15 minutes at most?
> > > > > > > > > > > >
> > > > > > > > > > > > >As far as your patch goes, surely rejecting more SSK
> > > > > > > > > > > > > requests would be
> > > > > > > > > > > >
> > > > > > > > > > > > counterproductive as it wastes bandwidth?
> > > > > > > > > > > >
> > > > > > > > > > > > Tests show the opposite: without the patch payload
> > > > > > > > > > > > output at stats page never exceeded 38%, with patch
> > > > > > > > > > > > it becomes 53% or little more after several minutes
> > > > > > > > > > > > upon node restart. So, with the patch SSK/CHK
> > > > > > > > > > > > forwarding behaviour 'feels' logical:
> > > > > > > > > > > >
> > > > > > > > > > > > without patch:
> > > > > > > > > > > > - just several CHKs, and over over 100 SSKs very
> > > > > > > > > > > > typical.
> > > > > > > > > > > >
> > > > > > > > > > > > with patch:
> > > > > > > > > > > > - most of the time (say, 75%) number of currently
> > > > > > > > > > > > forwarded CHK requests+inserts approximately equals
> > > > > > > > > > > > to the number of SSK requests+inserts (i.e. 10-25
> > > > > > > > > > > > each, depending on set bandwidth limit); - sometimes
> > > > > > > > > > > > (say, 10%) CHK requests start to prevail, but current
> > > > > > > > > > > > SSK requests+inserts seems never go below the amount
> > > > > > > > > > > > which CHK get at max without patch (i.e. 6-10). This
> > > > > > > > > > > > is very typical when number of CHK inserts gets
> > > > > > > > > > > > several times higher than CHK requests (close fast
> > > > > > > > > > > > peer inserts something really large?). - other times
> > > > > > > > > > > > (say, 15%) CHK requests+inserts flow does not
> > > > > > > > > > > > saturate bandwidth, and number of SSK requests
> > > > > > > > > > > > quickly climbs to 50 or even over 100+ as it
> > > > > > > > > > > > typically gets without the patch.
> > > > > > > > > > > >
> > > > > > > > > > > > That's for LBN. Raising input bandwidth allotment,
> > > > > > > > > > > > number of SSKs quickly grows resembling the situation
> > > > > > > > > > > > without the patch.
> > > > > > > > > > > >
> > > > > > > > > > > > So that's why I suggest reserving bandwidth for 2 CHK
> > > > > > > > > > > > transfers; 3 would kill SSKs, 1 still makes SSKs to
> > > > > > > > > > > > seriously prevail over CHKs (but nonetheless gives
> > > > > > > > > > > > quite better ratio, so is a legal value to try if the
> > > > > > > > > > > > value of 2 alarms you too much). Just, in case of
> > > > > > > > > > > > reserving bandwidth for 1 extra CHK the proposed
> > > > > > > > > > > > patch is not really needed: simply comment out the
> > > > > > > > > > > > line starting with "bandwidthLiabilityInput +=" and
> > > > > > > > > > > > decrease 90 seconds constant to 80 (10 seconds is
> > > > > > > > > > > > roughly how much 33.6Kbod modem takes to transmit a
> > > > > > > > > > > > single CHK - using anything noticeably slower than
> > > > > > > > > > > > 28800/33600bod for freenet will not ever work well
> > > > > > > > > > > > anyway).
> > > > > > > > > > > >
> > > > > > > > > > > > >Shouldn't a slow node accept those requests it's
> > > > > > > > > > > > > likely to be able to handle?
> > > > > > > > > > > >
> > > > > > > > > > > > Considering the very high chance of SSK request
> > > > > > > > > > > > failures (at lest 92%), I would say the answer is no.
> > > > > > > > > > > > But with sane SSK failure rate (say 75% or below) SSK
> > > > > > > > > > > > requests would likely not waste the limited thus
> > > > > > > > > > > > precious LBN bandwidth so fruitlessly.
> > > > > > > > > > > >
> > > > > > > > > > > > The problem, in my belief, is too small size of UDP
> > > > > > > > > > > > packets if SSK requests prevail: PPP(oE)/TCP/FNP
> > > > > > > > > > > > overhead becomes too large while LBNs, unlike faster
> > > > > > > > > > > > link nodes, almost never coalesce packets, obviously.
> > > > > > > > > > > >
> > > > > > > > > > > > ----- toad at zceUWxlSaHLmvEMnbr4RHnVfehA -----
> > > > > > > > > > > > 2007.04.27 - 17:19:24GMT -----
> > > > > > > > > > > >
> > > > > > > > > > > > The current algorithm is working, on most nodes, far
> > > > > > > > > > > > better than it has in *ages*. I'm at 62% of a 700MB
> > > > > > > > > > > > ISO, I started inserting it yesterday morning, and
> > > > > > > > > > > > only a few of my peers are backed off - frequently
> > > > > > > > > > > > none are backed off, right now it's 11 connected, 6
> > > > > > > > > > > > backed off, which is more backed off than I've seen
> > > > > > > > > > > > for quite a while.
> > > > > > > > > > > >
> > > > > > > > > > > > Re failure tables: Yes it is extremely dangerous. It
> > > > > > > > > > > > can result in self-reinforcing key censorship, either
> > > > > > > > > > > > as an attack or just occurring naturally. This
> > > > > > > > > > > > happened on 0.5. And the hit ratio is only for CHKs
> > > > > > > > > > > > iirc.
> > > > > > > > > > > >
> > > > > > > > > > > > Even LBNs don't often send local RejectedOverload's
> > > > > > > > > > > > on SSKs *once they have accepted them*. They may
> > > > > > > > > > > > relay downstream RO's but that is not fatal. And if
> > > > > > > > > > > > they reject some requests, so what, it's a slow node,
> > > > > > > > > > > > it's bound to reject some requests with the current
> > > > > > > > > > > > load balancing system.
> > > > > > > > > > > >
> > > > > > > > > > > > 10-15 minutes would be interesting. We already show a
> > > > > > > > > > > > circle and histogram of nearby nodes from swapping
> > > > > > > > > > > > and of our peers, you'd just have to add another one.
> > > > > > > > > > > > It would be good to have a visual proof that routing
> > > > > > > > > > > > is working on the level of adhering to node
> > > > > > > > > > > > specialisations. I didn't expect it to be working
> > > > > > > > > > > > given the load: I'm surprised that it does, it's an
> > > > > > > > > > > > interesting result.
> > > > > > > > > > > >
> > > > > > > > > > > > Packet size has nothing to do with it, ethernet has a
> > > > > > > > > > > > 1472 byte maximum. Dial-up has 576 bytes max, but we
> > > > > > > > > > > > ignore it, and use fragmented packets (this sucks,
> > > > > > > > > > > > obviously, as it greatly increases the chance of
> > > > > > > > > > > > losing a packet and having to retransmit it).
> > > > > > > > > > > >
> > > > > > > > > > > > Please explain why the patch doesn't result in never
> > > > > > > > > > > > accepting a single SSK?
> > > > > > > > > > > >
> > > > > > > > > > > > ----- Anonymous at o9_0DTuZniSf_+oDmRsonByWxsI -----
> > > > > > > > > > > > 2007.04.27 - 19:31:14GMT -----
> > > > > > > > > > > >
> > > > > > > > > > > > >Packet size has nothing to do with it, ethernet has
> > > > > > > > > > > > > a 1472 byte maximum.
> > > > > > > > > > > >
> > > > > > > > > > > > Dial-up has 576 bytes max, but we ignore it, and use
> > > > > > > > > > > > fragmented packets (this sucks, obviously, as it
> > > > > > > > > > > > greatly increases the chance of losing a packet and
> > > > > > > > > > > > having to retransmit it).
> > > > > > > > > > > >
> > > > > > > > > > > > I am talking about typical/average packet size, not
> > > > > > > > > > > > MTU. LBNs, unlike faster nodes, rarely have a chance
> > > > > > > > > > > > to coalesce reject responses (over max 100ms), and
> > > > > > > > > > > > thus send improportionally more tiny packets
> > > > > > > > > > > > resulting in much higher protocols overhead. Thus
> > > > > > > > > > > > having LBNs to mostly cater SSKs not CHKs results in
> > > > > > > > > > > > lowest imaginable usefulness of LBNs for network as a
> > > > > > > > > > > > whole.
> > > > > > > > > > > >
> > > > > > > > > > > > BTW in my experience typical/default dialup/PPP MTU
> > > > > > > > > > > > is 1500 minus link level headers, like ethernet. 576
> > > > > > > > > > > > is a reasonable adjustment for interactive traffic
> > > > > > > > > > > > like ssh but I fail to remember if it was used as
> > > > > > > > > > > > default since the time the super fast 28800 bod
> > > > > > > > > > > > modems became common.
> > > > > > > > > > > >
> > > > > > > > > > > > :) 1400+ is the typical size of GPRS PPP packets too,
> > > > > > > > > > > > : and the same
> > > > > > > > > > > >
> > > > > > > > > > > > holds true for other popular wireless mediae like
> > > > > > > > > > > > BlueTooth or WiFi; so I have no concerns regarding IP
> > > > > > > > > > > > fragmentation.
> > > > > > > > > > > >
> > > > > > > > > > > > > Please explain why the patch doesn't result in
> > > > > > > > > > > > > never accepting a single SSK?
> > > > > > > > > > > >
> > > > > > > > > > > > I can not. :) Can you explain why the current code
> > > > > > > > > > > > that penalizes CHKs still gives 5% for them, even if
> > > > > > > > > > > > CHKs are 25 times larger and similarly less frequent
> > > > > > > > > > > > so have really hard time to arrive at the exact
> > > > > > > > > > > > moment when bandwidth liability is not maxed out?
> > > > > > > > > > > >
> > > > > > > > > > > > Seriously, I believe that goes with 2 facts:
> > > > > > > > > > > >
> > > > > > > > > > > > - SSK requests are much more frequent, so any
> > > > > > > > > > > > temporary drop of CHK requests level enables node to
> > > > > > > > > > > > quickly get a bunch of new SSKs accepted for
> > > > > > > > > > > > processing; - the large CHK requests (at times while
> > > > > > > > > > > > they prevail over SSKs) tend to hit other limits too,
> > > > > > > > > > > > like "output bandwidth liability", "Insufficient
> > > > > > > > > > > > input/output bandwidth" throttles. Then the small SSK
> > > > > > > > > > > > requests quickly pick up all the remaining bandwidth
> > > > > > > > > > > > bits.
> > > > > > > > > > > >
> > > > > > > > > > > > But currently I do not have relevant statistics to
> > > > > > > > > > > > prove that.
> > > > > > > > > > > >
> > > > > > > > > > > > Anyway, please commit the following patch - it should
> > > > > > > > > > > > equal out bandwidth rights for CHKs and SSKs at least
> > > > > > > > > > > > half way toward fair/expected distribution (and the
> > > > > > > > > > > > change will make any difference for high-/over-loaded
> > > > > > > > > > > > nodes only). Once most of my peers (and their peers)
> > > > > > > > > > > > update, I will study the new node traffic forwarding
> > > > > > > > > > > > efficiency and behavior at different bandwidth limits
> > > > > > > > > > > > and with different penalization levels again - and
> > > > > > > > > > > > then will be in better position to prove the original
> > > > > > > > > > > > proposal of reserving bandwidth for 2 CHKs is optimal
> > > > > > > > > > > > (or maybe withdraw it).
> > > > > > > > > > > >
> > > > > > > > > > > > ===
> > > > > > > > > > > > diff --git a/freenet/src/freenet/node/NodeStats.java
> > > > > > > > > > > > b/freenet/src/freenet/node/NodeStats.java
> > > > > > > > > > > > index 3b091b4..98c82c3 100644
> > > > > > > > > > > > --- a/freenet/src/freenet/node/NodeStats.java
> > > > > > > > > > > > +++ b/freenet/src/freenet/node/NodeStats.java
> > > > > > > > > > > > @@ -399,9 +399,8 @@ public class NodeStats implements
> > > > > > > > > > > > Persistable {
> > > > > > > > > > > >
> > > > > > > > > > > > successfulSskFetchBytesSentAverage.currentValue() *
> > > > > > > > > > > > node.getNumSSKRequests() +
> > > > > > > > > > > >
> > > > > > > > > > > > successfulChkInsertBytesSentAverage.currentValue() *
> > > > > > > > > > > > node.getNumCHKInserts() +
> > > > > > > > > > > >
> > > > > > > > > > > > successfulSskInsertBytesSentAverage.currentValue() *
> > > > > > > > > > > > node.getNumSSKInserts();
> > > > > > > > > > > > - bandwidthLiabilityOutput +=
> > > > > > > > > > > > getSuccessfulBytes(isSSK, isInsert,
> > > > > > > > > > > > false).currentValue(); double
> > > > > > > > > > > > bandwidthAvailableOutput = -
> > > > > > > > > > > > node.getOutputBandwidthLimit() * 90; // 90 seconds at
> > > > > > > > > > > > full power; we have to leave some time for the search
> > > > > > > > > > > > as well +
> > > > > > > > > > > > node.getOutputBandwidthLimit() * 80; // 80 seconds at
> > > > > > > > > > > > full power; we have to leave some time for the search
> > > > > > > > > > > > as well bandwidthAvailableOutput *=
> > > > > > > > > > > > NodeStats.FRACTION_OF_BANDWIDTH_USED_BY_REQUESTS;
> > > > > > > > > > > > if(bandwidthLiabilityOutput >
> > > > > > > > > > > > bandwidthAvailableOutput) {
> > > > > > > > > > > > preemptiveRejectReasons.inc("Output bandwidth
> > > > > > > > > > > > liability"); @@ -413,9 +412,8 @@ public class
> > > > > > > > > > > > NodeStats implements Persistable {
> > > > > > > > > > > >
> > > > > > > > > > > > successfulSskFetchBytesReceivedAverage.currentValue()
> > > > > > > > > > > > * node.getNumSSKRequests() +
> > > > > > > > > > > >
> > > > > > > > > > > > successfulChkInsertBytesReceivedAverage.currentValue(
> > > > > > > > > > > >) * node.getNumCHKInserts() +
> > > > > > > > > > > >
> > > > > > > > > > > > successfulSskInsertBytesReceivedAverage.currentValue(
> > > > > > > > > > > >) * node.getNumSSKInserts();
> > > > > > > > > > > > - bandwidthLiabilityInput +=
> > > > > > > > > > > > getSuccessfulBytes(isSSK, isInsert,
> > > > > > > > > > > > true).currentValue(); double bandwidthAvailableInput
> > > > > > > > > > > > = -
> > > > > > > > > > > > node.getInputBandwidthLimit() * 90; // 90 seconds at
> > > > > > > > > > > > full power
> > > > > > > > > > > > + node.getInputBandwidthLimit()
> > > > > > > > > > > > * 80; // 80 seconds at full power
> > > > > > > > > > > > if(bandwidthLiabilityInput >
> > > > > > > > > > > > bandwidthAvailableInput) {
> > > > > > > > > > > > preemptiveRejectReasons.inc("Input bandwidth
> > > > > > > > > > > > liability"); return "Input bandwidth liability"; ===
> > > > > > > > > > > >
> > > > > > > > > > > > ----- toad at zceUWxlSaHLmvEMnbr4RHnVfehA -----
> > > > > > > > > > > > 2007.04.28 - 17:05:53GMT -----
> > > > > > > > > > > >
> > > > > > > > > > > > Why does assuming 80 seconds instead of 90 help? I
> > > > > > > > > > > > would have expected it to make the situation worse.
> > > > > > > > > > > >
> > > > > > > > > > > > Isn't what you want to increment the value you are
> > > > > > > > > > > > multiplying the CHK byte counters by if the request
> > > > > > > > > > > > is an SSK? In any case I'm not convinced - we accept
> > > > > > > > > > > > 32x as many SSKs as CHKs precisely because they use
> > > > > > > > > > > > 32x less bandwidth. As far as I can see incrementing
> > > > > > > > > > > > the CHK counts but only on a CHK would just result in
> > > > > > > > > > > > us never accepting an SSK...
> > > > > > > > > > > >
> > > > > > > > > > > > But by all means continue to investigate.
> > > > > > > > > > > >
> > > > > > > > > > > > ----- mrogers at UU62+3E1vKT1k+7fR0Gx7ZN2IB0 -----
> > > > > > > > > > > > 2007.04.30 - 19:36:36GMT -----
> > > > > > > > > > > >
> > > > > > > > > > > > > we accept 32x as many SSKs as CHKs precisely
> > > > > > > > > > > > > because they use 32x less
> > > > > > > > > > > >
> > > > > > > > > > > > bandwidth.
> > > > > > > > > > > >
> > > > > > > > > > > > Sorry but I don't understand the rationale behind
> > > > > > > > > > > > this. It seems to be based on the assumption that
> > > > > > > > > > > > equal resources should be allocated to SSKs and CHKs,
> > > > > > > > > > > > regardless of whether there's equal demand for
> > > > > > > > > > > > resources. If we're only getting, say, 16 times as
> > > > > > > > > > > > many SSK requests as CHK requests, would we reject
> > > > > > > > > > > > CHK requests to keep things "fair"?
> > > > > > > > > > > >
> > > > > > > > > > > > ----- toad at zceUWxlSaHLmvEMnbr4RHnVfehA -----
> > > > > > > > > > > > 2007.05.02 - 16:13:52GMT -----
> > > > > > > > > > > >
> > > > > > > > > > > > Why should CHKs be prioritised over SSKs?
> > > > > > > > > > > >
> > > > > > > > > > > > What do you think of the patch I committed anyway?
> > > > > > > > > > >
> > > > > > > > > > > ----- Anonymous at o9_0DTuZniSf_+oDmRsonByWxsI -----
> > > > > > > > > > > 2007.05.02 - 17:03:52GMT -----
> > > > > > > > > > >
> > > > > > > > > > > > Why should CHKs be prioritised over SSKs?
> > > > > > > > > > >
> > > > > > > > > > > Because SSK success ratio is extremely low (remember
> > > > > > > > > > > the example I gave within initial message in the
> > > > > > > > > > > thread: 8100 rejected requests for the same SSK key
> > > > > > > > > > > within 35 hours, and uncounted amount of the same key
> > > > > > > > > > > requests resulted in DNF - and such key is nowhere near
> > > > > > > > > > > being alone); linear programming would certainly
> > > > > > > > > > > suggest that SSK requests like they currently are
> > > > > > > > > > > should be totally disabled. I do not propose anything
> > > > > > > > > > > as drastic; but as SSKs currently use bandwidth very
> > > > > > > > > > > inefficiently I propose to tone them down heuristically
> > > > > > > > > > > to approximately CHK level while node is short on
> > > > > > > > > > > bandwidth (but let SSKs go as much as sending node
> > > > > > > > > > > needs if spare bandwidth available).
> > > > > > > > > > >
> > > > > > > > > > > [not that I meant to speak instead of mrogers]
> > > > > > > > > > >
> > > > > > > > > > > ----- mrogers at UU62+3E1vKT1k+7fR0Gx7ZN2IB0 -----
> > > > > > > > > > > 2007.05.03 - 13:54:38GMT -----
> > > > > > > > > > >
> > > > > > > > > > > >> Why should CHKs be prioritised over SSKs?
> > > > > > > > > > > >
> > > > > > > > > > > > Because SSK success ratio is extremely low
> > > > > > > > > > >
> > > > > > > > > > > That doesn't make sense for two reasons:
> > > > > > > > > > >
> > > > > > > > > > > 1) rejecting SSKs will make the SSK success ratio
> > > > > > > > > > > worse, not better 2) "SSK not found" is useful
> > > > > > > > > > > information - for example, that's how you discover the
> > > > > > > > > > > current version of a USK - but "SSK rejected for not
> > > > > > > > > > > being a CHK" is not useful to anyone
> > > > > > > > > > >
> > > > > > > > > > > Let me use an analogy: you're designing a Cisco router.
> > > > > > > > > > > Some of the packets it gets asked to forward will be
> > > > > > > > > > > small SSH packets, others will be large HTTP packets.
> > > > > > > > > > > Do you say "half our resources should go to SSH because
> > > > > > > > > > > we don't want to prioritise HTTP, so we'll only forward
> > > > > > > > > > > one HTTP packet for every 32 SSH packets"? If you
> > > > > > > > > > > answered yes, you just lost your job at Cisco. The
> > > > > > > > > > > router's job is to deliver packets to the best of its
> > > > > > > > > > > ability, not to decide what kind of packets the end
> > > > > > > > > > > hosts "should" be sending.
> > > > > > > > > >
> > > > > > > > > > ----- Anonymous ----- 2007.05.03 - 18:37:00GMT -----
> > > > > > > > > >
> > > > > > > > > > lets build an extreme case:
> > > > > > > > > > There is a packet type which is 1 MB in size and one
> > > > > > > > > > which is 1 byte in size. Both get constantly send to a
> > > > > > > > > > router at a higher rate then the routers bandwidth quota
> > > > > > > > > > allows it to forward the packets. If the following rules
> > > > > > > > > > apply not a single 1 MB packet will get served: 1. the
> > > > > > > > > > router doesn't care for the size of the packet or
> > > > > > > > > > penalises any kind of packet, all are considered equal 2.
> > > > > > > > > > if a packet arrives and the remaining bandwidth quota
> > > > > > > > > > doesn't allow to forward it, it gets instantly rejected
> > > > > > > > > > 3. no queueing of incomming packets is done (with
> > > > > > > > > > part-allocation of available bandwidth if packet size
> > > > > > > > > > exceed the free quota)
> > > > > > > > > >
> > > > > > > > > > Afaik this is a possible situation for freenet, correct
> > > > > > > > > > me if I am wrong.
> > > > > > > > >
> > > > > > > > > ----- mrogers at UU62+3E1vKT1k+7fR0Gx7ZN2IB0 ----- 2007.05.04
> > > > > > > > > - 11:15:09GMT -----
> > > > > > > > >
> > > > > > > > > You're right, that pretty much describes the problem. I'm
> > > > > > > > > suggesting that we should fix it by modifying step 2:
> > > > > > > > >
> > > > > > > > > 2. if a packet arrives and the remaining bandwidth quota
> > > > > > > > > doesn't allow to forward *an average packet*, it gets
> > > > > > > > > instantly rejected
> > > > > > > > >
> > > > > > > > > The average is calculated over all packets, large and
> > > > > > > > > small. In other words we ask:
> > > > > > > > >
> > > > > > > > > a) how much bandwidth does a packet use, on average?
> > > > > > > > > b) is there enough bandwidth for another average packet?
> > > > > > > > >
> > > > > > > > > Let's say 75% of packets are 1 byte in size and 25% are 1
> > > > > > > > > MB in size, so the average is 262,144.75 bytes. We accept
> > > > > > > > > packets (large or small) if we have at least 262,144.75
> > > > > > > > > bytes of bandwidth left in the quota, and reject them
> > > > > > > > > otherwise. If there's a long stream of 1 byte packets
> > > > > > > > > followed by a 1 MB packet we might go over quota
> > > > > > > > > temporarily, but we'll match the quota in the long term.
> > > > > > > > >
> > > > > > > > > ----- Anonymous at o9_0DTuZniSf_+oDmRsonByWxsI -----
> > > > > > > > > 2007.05.10 - 21:01:58GMT -----
> > > > > > > > >
> > > > > > > > > Oh no, getting stuff instantly rejected is most often not
> > > > > > > > > good (an exception would be certain kinds of realtime
> > > > > > > > > traffic, but that is not applicable for freenet at all). I
> > > > > > > > > have some experience with independant/competing ISPs and
> > > > > > > > > their broken traffic shaping routers that were always
> > > > > > > > > dropping packets not fitting current shaping limits; TCP
> > > > > > > > > performance was
> > > > > > > > > experiencing major hit there, and several TCP connections
> > > > > > > > > running under the same shaping were always taking seriously
> > > > > > > > > unfair bandwidth share (unless you get quite long intervals
> > > > > > > > > for stats, like 10+ minutes). Changing shaping processing
> > > > > > > > > by queueing an over-quota packet (even a single packet
> > > > > > > > > queue!) till the calculated average bandwidth allows to
> > > > > > > > > send the packet (thus in the end increasing roundtrip
> > > > > > > > > slightly) was always sufficient for TCP flow to work at
> > > > > > > > > 100% of the shaped level, and having simultaneous TCP
> > > > > > > > > streams to very equally share available bandwidth even for
> > > > > > > > > sub-second stats intervals, and there were no other working
> > > > > > > > > solution found (aside raising the shaping limit above the
> > > > > > > > > maximum speed of TCP peers).
> > > > > > > > >
> > > > > > > > > I am not sure that can be directly applied to the current
> > > > > > > > > freenet networking code; honestly, the mechanism of first
> > > > > > > > > quickly accepting packets and then slowly picking them
> > > > > > > > > using some kind of filters looks unneccessary complicated
> > > > > > > > > and performance inoptimal, to say least: I have another
> > > > > > > > > bright example why - the mechanism quite resembles the
> > > > > > > > > traditional O/S network packets handling (with received
> > > > > > > > > packets extracted from NIC at highest priority - during
> > > > > > > > > hardware interrupt, and then having CPU/server business
> > > > > > > > > logic failing to process all received packets leading to
> > > > > > > > > internal queues overflow), and after years and decades it
> > > > > > > > > is generally agreed that such approach does not work well
> > > > > > > > > for server applications; instead, linux for several years
> > > > > > > > > already has mechanism named NAPI (which is optional for
> > > > > > > > > some NIC drivers - check kernel config, but default and
> > > > > > > > > mandatory for most server-grade and/or 1Gb NIC drivers):
> > > > > > > > > hardware interrupt just sets a flag/semaphore that NIC has
> > > > > > > > > received something, and instantly quits leaving the
> > > > > > > > > particular NIC interrupt line disabled (actual algorithm is
> > > > > > > > > a little bit more complex, allowing hardware interrupt to
> > > > > > > > > perform extraction of a very limited number of packets if
> > > > > > > > > the host is very idle). Then there is a lowest priority
> > > > > > > > > kernel thread ("software interrupt") woken up by the
> > > > > > > > > flag/semaphore starts reading packets from NIC into O/S
> > > > > > > > > queues (where user-level read()s get satisfied from),
> > > > > > > > > extracting only limited number of packets at a time (then
> > > > > > > > > yielding CPU for other runnable processes), and reenabling
> > > > > > > > > the NIC interrupts only when it managed to empty the
> > > > > > > > > hardware queue - with TCP flow control, and with the modern
> > > > > > > > > ethernet hardware flow control that works exceptionally
> > > > > > > > > well. Thus server business logic (i.e. useful work) running
> > > > > > > > > at priority much higher than software interrupt thread is
> > > > > > > > > never starved from CPU by hardware interrupts that first
> > > > > > > > > pull in packets which then result in CPU wasted to drop
> > > > > > > > > them from overflown system queue - resulting in smooth
> > > > > > > > > behaviour and best sustained performance.
> > > > > > > > >
> > > > > > > > > Or in short - on overload, delaying input packets
> > > > > > > > > reading/processing is better than dropping or rejecting
> > > > > > > > > them instantly.
> > > > > > > > >
> > > > > > > > > Toad - if you know a simple way to delay freenet reads from
> > > > > > > > > UDP socket in order to enforce configured input bandwidth
> > > > > > > > > limit, please do so. (And with that UDP read delay, I would
> > > > > > > > > be very interested to test freenet node without other input
> > > > > > > > > bandwidth limiters aside input bandwidth liability used -
> > > > > > > > > chances that the UDP socket read delay will be sufficient
> > > > > > > > > for quality shaping, with the valuable help of sending node
> > > > > > > > > tracking the roundtrip - an already well implemented
> > > > > > > > > feature).
> > > > > > > > >
> > > > > > > > > If the delay can not be done easily with the current
> > > > > > > > > codebase, I will consider doing major rewrite of the
> > > > > > > > > traffic accepting code part. Not of highest priority tho,
> > > > > > > > > due to anticipated large amount of work - but those high
> > > > > > > > > fruits look big and tasty.
> > > > > > > >
> > > > > > > > ----- mrogers at UU62+3E1vKT1k+7fR0Gx7ZN2IB0 ----- 2007.05.11 -
> > > > > > > > 14:56:37GMT -----
> > > > > > > >
> > > > > > > > > I am not sure that can be directly applied to the current
> > > > > > > > > freenet networking
> > > > > > > >
> > > > > > > > code;
> > > > > > > >
> > > > > > > > We're working on an idea called token-passing that's supposed
> > > > > > > > to address this: you can only send a search (request/insert)
> > > > > > > > to a peer if you have a flow control token from that peer. If
> > > > > > > > you don't have a token you either keep the search in a queue
> > > > > > > > until you receive a token, or send it to the next-best peer
> > > > > > > > if the queue is full.
> > > > > > > >
> > > > > > > > > the mechanism quite resembles the traditional O/S network
> > > > > > > > > packets handling
> > > > > > > >
> > > > > > > > (with received packets extracted from NIC at highest priority
> > > > > > > > - during hardware interrupt, and then having CPU/server
> > > > > > > > business logic failing to process all received packets
> > > > > > > > leading to internal queues overflow)
> > > > > > > >
> > > > > > > > Interesting point - in the new congestion control layer,
> > > > > > > > maybe the UDP reader shouldn't advance the receiver window
> > > > > > > > until the internal queues have dropped below a certain
> > > > > > > > size... but it might be tricky to implement because the
> > > > > > > > internal queues all belong to different threads...
> > > > > > > >
> > > > > > > > > If the delay can not be done easily with the current
> > > > > > > > > codebase, I will
> > > > > > > >
> > > > > > > > consider doing major rewrite of the traffic accepting code
> > > > > > > > part.
> > > > > > > >
> > > > > > > > This is due to be rewritten soon anyway, so now's probably a
> > > > > > > > good time to make suggestions.
> > > > > > > >
> > > > > > > > ----- Anonymous at o9_0DTuZniSf_+oDmRsonByWxsI ----- 2007.05.14
> > > > > > > > - 16:46:24GMT -----
> > > > > > > >
> > > > > > > > While token passing would indeed smooth the traffic out, it
> > > > > > > > feels excessive:
> > > > > > > >
> > > > > > > > - it adds extra traffic;
> > > > > > > > - it creates additional traffic patterns, that quite simplify
> > > > > > > > attacks (like those aiming at reliably proving that a
> > > > > > > > particular request originates from attacked node) against a
> > > > > > > > node which all connections are monitored (by ISP), and some
> > > > > > > > of them are fast but compromised (compromised peers).
> > > > > > > > - it requires to pull a multidimensional set of heurictics on
> > > > > > > > whom to send new token out of a thin air, and those
> > > > > > > > heuristics will tend to disagree for different connection
> > > > > > > > types.
> > > > > > > >
> > > > > > > > The method of delaying network reads (thats important - and
> > > > > > > > AFAIK the only major missing thing to get shaping rolling
> > > > > > > > smoothly already) should work similarly well (might be even
> > > > > > > > better): just consider the metric 'the current peer roundtrip
> > > > > > > > time is lower than the [peer] average roundtrip time' as
> > > > > > > > equivalence of 'the peer gave us few tokens', and enjoy the
> > > > > > > > bandwidth/crypt(CPU) free virtual token passing which obeys
> > > > > > > > both hardware/ISP traffic shaping imposed limits, as well as
> > > > > > > > software configured limits - whichever is stricter.
> > > > > > > >
> > > > > > > > So I currently discorage implementing explicit token passing,
> > > > > > > > in favor of lower, equially tasty fruit.
> > > > > > >
> > > > > > > ----- mrogers at UU62+3E1vKT1k+7fR0Gx7ZN2IB0 ----- 2007.05.17 -
> > > > > > > 21:40:27GMT -----
> > > > > > >
> > > > > > > > - it adds extra traffic
> > > > > > >
> > > > > > > Um, right. "Here are n tokens" takes about 6 bytes: two for the
> > > > > > > message type, two for the message size, and two for the number
> > > > > > > of tokens (we're never going to hand out more than 65535 tokens
> > > > > > > in one go). It uses less traffic than "Can I send you a
> > > > > > > request?" "Yes" "Here's the request", and it avoids a
> > > > > > > round-trip. It also uses less traffic than "Can I send you a
> > > > > > > request?" "No", because if you don't have a token, you don't
> > > > > > > need to ask!
> > > > > > >
> > > > > > > > - it creates additional traffic patterns, that quite simplify
> > > > > > > > attacks (like
> > > > > > >
> > > > > > > those aiming at reliably proving that a particular request
> > > > > > > originates from attacked node) against a node which all
> > > > > > > connections are monitored (by ISP), and some of them are fast
> > > > > > > but compromised (compromised peers).
> > > > > > >
> > > > > > > Please explain how handing my peer some tokens reveals anything
> > > > > > > about traffic patterns that wasn't already visible to traffic
> > > > > > > analysis. If they can see the requests and results going back
> > > > > > > and forth, who cares if they can also see the tokens?
> > > > > > >
> > > > > > > > - it requires to pull a multidimensional set of heurictics on
> > > > > > > > whom to send
> > > > > > >
> > > > > > > new token out of a thin air, and those heuristics will tend to
> > > > > > > disagree for different connection types.
> > > > > > >
> > > > > > > No magical heuristics are needed - we hand out tokens as long
> > > > > > > as we're not overloaded (measured by total queueing delay,
> > > > > > > including the bandwidth limiter). That alone should be enough
> > > > > > > to outperform the current system, because we'll avoid wasting
> > > > > > > traffic on rejected searches. Then we can start thinking about
> > > > > > > clever token allocation policies to enforce fairness when the
> > > > > > > network's busy, without imposing unnecessary limits when the
> > > > > > > network's idle, etc etc. But token passing doesn't depend on
> > > > > > > any such policy - it's just a lower-bandwidth alternative to
> > > > > > > pre-emptive rejection.
> > > > > >
> > > > > > ----- toad at zceUWxlSaHLmvEMnbr4RHnVfehA ----- 2007.05.19 -
> > > > > > 17:38:09GMT -----
> > > > > >
> > > > > > We hand out tokens when we're not overloaded? What if later on we
> > > > > > get overloaded? How exactly do we determine the total appropriate
> > > > > > number of tokens in the system?
> > > > > >
> > > > > > Token passing would be really nice, it would solve the flooding
> > > > > > problem and remove a lot of alchemy...
> > > > >
> > > > > ----- mrogers at UU62+3E1vKT1k+7fR0Gx7ZN2IB0 ----- 2007.05.20 -
> > > > > 11:19:36GMT -----
> > > > >
> > > > > We determine the appropriate number of tokens by experimentation:
> > > > > as we approach overload we produce tokens more and more slowly,
> > > > > until at the overload point we don't produce tokens at all. For
> > > > > example, delay between producing tokens = MAX_DELAY/(MAX_DELAY -
> > > > > currentDelay) seconds, or something similar.
> > > > >
> > > > > We stop producing tokens when all the buckets are full. To limit
> > > > > the number of tokens in circulation, we adjust the bucket sizes.
> > > > > Each peer's bucket starts at size 0, and is reset to 0 whenever the
> > > > > peer reconnects. Whenever we add a token to an empty bucket, we
> > > > > increase its size by 1. Thus if a peer doesn't use the tokens we
> > > > > give it (ie doesn't empty its bucket), its bucket stays small. If
> > > > > it uses the tokens we give it (ie empties its bucket), we increase
> > > > > the size of its bucket as long as we're not overloaded (the bucket
> > > > > size is only increased when a token is handed out, which doesn't
> > > > > happen when we're overloaded).
> > > >
> > > > ----- Anonymous at o9_0DTuZniSf_+oDmRsonByWxsI ----- 2007.05.25 -
> > > > 11:45:36GMT -----
> > > >
> > > > Even this brief description proposes 3 heuristics already:
> > > >
> > > > - "more slowly or something similar"
> > > > - "adjust bucket sizes"
> > > > - "stays small"
> > > >
> > > > No doubts complete practical implementation will involve quite more,
> > > > and I see no way to ensure they will all work smoothly for all the
> > > > wide variety of connection types.
> > > >
> > > > This also totally silences the burst problems, as well as decreasing
> > > > buckets during the bursts/overload periods. Kinda extreme case: if
> > > > you gave a node 5 tokens, and it decided to use them 3 minutes later
> > > > when the node got overloaded, what did you gain with the tokens? That
> > > > is a true Pandora box.
> > > >
> > > > In the end it is timing that matters, while tokens represent data
> > > > amount (and if you think of a formula time*bandwidth=data, then
> > > > bandwidth, generally speaking, is not constant due to highly
> > > > irregular traffic from different peers and other apps sharing the
> > > > same internet connection). Purely controlling the latter will always
> > > > be just a rough approximation of controlling the former, alas.
> > >
> > > ----- mrogers at UU62+3E1vKT1k+7fR0Gx7ZN2IB0 ----- 2007.05.25 -
> > > 17:20:00GMT -----
> > >
> > > > I see no way to ensure they will all work smoothly for all the wide
> > > > variety
> > >
> > > of connection types
> > >
> > > That may be true, but can you ensure that with the current mechanism?
> > >
> > > > if you gave a node 5 tokens, and it decided to use them 3 minutes
> > > > later when
> > >
> > > the node got overloaded, what did you gain with the tokens?
> > >
> > > It shouldn't ever reach that point, because when you give out 4 tokens
> > > and get a burst that nearly overloads the node, you'll stop increasing
> > > the size of the buckets.
> > >
> > > > Purely controlling the latter will always be just a rough
> > > > approximation of
> > >
> > > controlling the former, alas.
> > >
> > > True, it's only a rough approximation and traffic is bursty and we
> > > can't predict the future, but all those things also apply to the
> > > current system.
> >
> > ----- Anonymous at o9_0DTuZniSf_+oDmRsonByWxsI ----- 2007.05.25 -
> > 20:35:30GMT -----
> >
> > - I gave 4 tokens to peer A, and 4 tokens for peer B;
> > - peer A used up the token in one burst, causing local bandwidth overage
> > already.
> > - now if peer B decides to use up the tokens, my bandwidth is already
> > flooded badly.
> >
> > - I gave 2 tokens (generally: very small amount) to peer A, and 2 tokens
> > to peer B at this time;
> > - the peer A used up both of them, but peer B does not have anything to
> > request for now.
> > - as result, the available bandwidth is only half-loaded until peer A
> > explicitly given another few tokens; but giving away small amounts of
> > tokens puts traffic overhead (often in form of small sized packets with
> > highest overhead), and speed of feeding small packs of tokens is
> > seriously limited by roundtrip delays.
> >
> > Thus nothing is really gained with tokens, and fighting that situation
> > sounds fruitless, and the only reasonable approach is to control the
> > roundtrip delay instead of fighting it, by delaying network reads as
> > needed to shape incoming traffic. This gives sending node not just boolen
> > flag can/cannot send immediatelly, but certain number to estimate optimal
> > outgoing interpacket delay toward a particular peer.
> >
> > ----- mrogers at UU62+3E1vKT1k+7fR0Gx7ZN2IB0 ----- 2007.05.26 - 19:31:25GMT
> > -----
> >
> > You're making the jump from 0 to 4 tokens as if there are no intermediate
> > stages. If 4 searches are enough to overload the node, then after you
> > give 2 tokens each to A and B, you'll get a burst and stop increasing the
> > size of the buckets. You should never reach a situation where there are
> > more tokens in circulation than you can handle simultaneously.
> >
> > You're also confusing the number of tokens with the size of the buckets
> > (probably my fault for not explaining it properly). If you give 2 tokens
> > each to A and B, and A uses its tokens but B doesn't, you're free to give
> > 2 more tokens to A; there's no reason for A to starve just because B is
> > holding tokens. The only effect of B holding tokens is to limit the size
> > of the bursts you can get from A to a level that will be safe even if you
> > simultaneously get a burst from B. To avoid making these limits too
> > strict, we start with small buckets and only increase the size of a
> > bucket when it's empty, so idle peers are limited to smaller bursts than
> > active peers, but the total burst size is still limited to what we can
> > handle.
> >
> > Obviously we should also have TCP-style congestion control between peers,
> > but that's not sufficient for network-wide load limiting in my opinion
> > (eg look at the original Gnutella, which used TCP between peers but still
> > had massive load limiting problems).
>
> ----- Anonymous at o9_0DTuZniSf_+oDmRsonByWxsI ----- 2007.05.27 -
> 08:54:29GMT -----
>
> Why you suppose each peer submits a stable flow of traffic? I might be
> downloading long and time lengthy file, gaining a bunch of tokens from you;
> and then as download finishes, I still possess alot of tokens?
>
> As you start issuing tokens is smaller chunks, you experience higher
> overhead from small token packets which failed to coalesce within thin time
> frame.
>
> TCP style congestion control (ECN) is not between peers; its existance is
> primarily targetted at ECN being directly supported by all (most) TCP/IP
> routers - without ECN or with ECN not supported by routers along the path
> TCP flow control enforced by packet drops only (when roudtrip measurements
> happen to fail predicting real momentarily network load).
>
> ----- mrogers at UU62+3E1vKT1k+7fR0Gx7ZN2IB0 ----- 2007.05.27 - 15:06:51GMT
> -----
>
> > Why you suppose each peer submits a stable flow of traffic?
>
> I don't, that's why I have frequently mentioned bursts.
>
> > I might be downloading long and time lengthy file, gaining a bunch of
>
> tokens from you; and then as download finishes, I still possess alot of
> tokens?
>
> Yes, if I have previously been able to cope with large bursts of traffic
> it's possible I will give you a large number of tokens. If not, I won't. So
> what's the problem?
>
> > As you start issuing tokens is smaller chunks, you experience higher
>
> overhead from small token packets which failed to coalesce within thin time
> frame.
>
> The problem of coalescing small messages on low-bandwidth links is not
> specified to token-passing. It also applies to the current mechanism, with
> its "can I send you a search?" "yes/no" messages that would be eliminated
> by token-passing.
>
> Why you keep talking about ECN I have no idea... are you suggesting that
> dropping/marking Freenet searches would have a similar effect to
> dropping/marking TCP packets in ECN? I don't think the two cases are
> comparable: in TCP you have a stream of packets between the same endpoints,
> so it makes sense to ask the sender to slow down if one of the routers is
> overloaded. In Freenet each search is routed independently to a different
> location, so it makes no sense to ask the sender to slow down if one of the
> nodes is overloaded - future searches handled by that node will come from
> different senders anyway. What you need to do is ask the overloaded node's
> neighbours to put less load on it. If that means they can accept fewer
> searches, then they should ask their neighbours to put less load on them,
> and so on.
>
> ----- Anonymous at o9_0DTuZniSf_+oDmRsonByWxsI ----- 2007.05.27 -
> 18:38:46GMT -----
>
> > Yes, if I have previously been able to cope with large bursts of traffic
>
> it's possible I will give you a large number of tokens. If not, I won't. So
> what's the problem?
>
> Once several dormant peers start sending new traffic at approximately the
> same time, the tokens passing mechanism have no even teoretical chance to
> avoid bandwidth overages/packets drops. More subtle mechanisms needed in
> order for sending nodes to know/decide not only about that fact that more
> traffic can be sent, but also how fast that should be done if there is more
> than one packet to send. Once such mechanisms are correctly implemented
> (and in noticeable part they already are), I see no advantages the explicit
> tokens passing could add.
>
> > so it makes no sense to ask the sender to slow down if one of the nodes
> > is
>
> overloaded
>
> Oh, why it could be so? Requests for keys with close locations are likely
> to get routed via the same overloaded node, and with peer locations pattern
> I keep observing the 'closeness' might easily be as wide as 0.4 and even
> more (the range of locations that prefer the same peer). The requests sent
> recently (in term of hops passed, not time) show even distribution of the
> keys along the 0..1 space, so pushing 40% of traffic at a single peer and
> disregarding his overload cries can not be seen as good.
>
> The ECN distinguishing feature is that congestion/impending overload shared
> state gets maintained at all devices along the route (including endpoints)
> that at least potentially do traffic shaping (due to explicit settings or
> just overload). Lacking it, both TCP and FNP have to resort downto
> carefully tracking roundtrips, scurpuluously calculating all delays at
> routers and final hosts in order to react upon even minor degradations
> quickly (but smoothly). FNP gets more complicated, as packet processing
> efforts (including all the encryption/decryption) are not as negligible as
> with TCP, but not indoable - the packets/protocol already carry the
> temporal information implicitly, it just has to be handled a little bit
> more careful.
>
> OTOH, adding explicit auxilarly traffic (be it tokens assing or whatever)
> creates a certain dilemma: trying to maximize the variable bandwidth usage
> without overages, the additional even little (but for many links, not so
> little due to the massive FNP+UDP+IP enveloping) overhead might turn out to
> be the bit that still causes the overages (in fact, the 'bit' in extremely
> unluky events flow can get up to 20% of traffic). Isn't it better to keep
> using simpler protocol, maybe aiming it at 98% load if overages are known
> to cause unreasonably frequent packet drops, or just believed to be
> absolute evil?
>
>
> On a slightly different topic, how about wireless connections like
> radioethernet: high bandwidth and higher-than-average link delays are
> combined with constant non-zero packets drop rate (0.1-2%, but sometimes up
> to 5% in large city daytime, or in industrial area). Similar things with
> satellite links, during bad weather or in polar areas where any dish size
> is almost never sufficient. Explicitly passing tokens would be dangerous
> because of very high bursts: there might be 500KB data en-route for
> unidirectional SOHO grade satellite link, 1MB for bidirectional one. But if
> outstanding several hundreds tokens is not feasible and a little over a
> dozen KB is a limit, such links will be usable at 2-5% of available
> bandwidth at most.
>
> (You know how does TCP behave over such links? During periods of lower drop
> rate it works more or less acceptably, especially if you aren't in haste.
> At other times people simply get a teabrake or find another task for the
> time being. Solution here could be SCTP like protocols but they are very
> inmature and unpopular, and unlikely suit freenet needs).
>
> ----- mrogers at UU62+3E1vKT1k+7fR0Gx7ZN2IB0 ----- 2007.05.28 - 22:10:09GMT
> -----
>
> > Once several dormant peers start sending new traffic at approximately the
>
> same time, the tokens passing mechanism have no even teoretical chance to
> avoid bandwidth overages/packets drops.
>
> We're going in circles here. As I've already said, you never have more
> tokens outstanding than you can handle if they come back *simultaneously*.
> So I will only allow you to accumulate a large number of tokens if I can
> handle all those tokens, and all other outstanding tokens, being used at
> once. We don't have any magic way of determining how many tokens we can
> handle at once, so we *gradually* increase the limits until we get close to
> overload.
>
> > More subtle mechanisms needed in order for sending nodes to know/decide
> > not
>
> only about that fact that more traffic can be sent, but also how fast that
> should be done if there is more than one packet to send.
>
> Yes, we need a TCP-like mechanism to avoid congestion between peers, but
> that's not enough to avoid overloading the peers themselves (rather than
> the individual links).
>
> > pushing 40% of traffic at a single peer and disregarding his overload
> > cries
>
> can not be seen as good
>
> When did I say we should ignore overload? I said the overloaded node's
> neighbours should respond, rather than the source of the traffic, because
> the overloaded node's neighbours have more control over the amount of load
> it receives than a source elsewhere on the network.
>
> > The ECN distinguishing feature is that congestion/impending overload
> > shared
>
> state gets maintained at all devices along the route
>
> But my point was that in FNP there's no concept of a 'route' as there is in
> TCP. A series of TCP packets will travel along (more or less) the same
> route between the same endpoints. A series of FNP requests will travel
> along diverging routes to completely different endpoints. So asking the
> source to slow down when it hits an overloaded node is shutting the stable
> door after the horse has bolted: the source has already moved on to some
> other route that might be more or less loaded than the current route.
>
> > Isn't it better to keep using simpler protocol
>
> Sorry, I don't see how the current backoff/throttling/preemptive rejection
> mechanisms are simpler than token-passing. Equally complicated, maybe, but
> not less. :-)
>
> > Solution here could be SCTP like protocols but they are very inmature and
>
> unpopular, and unlikely suit freenet needs
>
> Yup, when I was working on the new congestion control design last year I
> considered copying DCCP or TCP Vegas to be more loss-tolerant (and it's
> still a possibility, if you want to design and document it). But in the end
> I decided the rest of the world was going to carry on using TCP, no matter
> how unsuitable, and the world's networks would be made suitable for TCP by
> hook or by crook (or by ugly MAC-layer retransmission hacks), so we could
> just copy TCP and let the layer 2 engineers solve the problem. :-)
----- mrogers at UU62+3E1vKT1k+7fR0Gx7ZN2IB0 ----- 2007.05.28 - 22:10:09GMT
-----
> Once several dormant peers start sending new traffic at approximately the
same time, the tokens passing mechanism have no even teoretical chance to
avoid bandwidth overages/packets drops.
We're going in circles here. As I've already said, you never have more tokens
outstanding than you can handle if they come back *simultaneously*. So I will
only allow you to accumulate a large number of tokens if I can handle all
those tokens, and all other outstanding tokens, being used at once. We don't
have any magic way of determining how many tokens we can handle at once, so
we *gradually* increase the limits until we get close to overload.
----- toad at zceUWxlSaHLmvEMnbr4RHnVfehA ----- 2007.05.29 - 01:26:17GMT -----
Okay, so just like the current code, we avoid timeouts by sacrificing
bandwidth - sometimes, sacrificing A LOT of bandwidth. Is that bad?
----- mrogers at UU62+3E1vKT1k+7fR0Gx7ZN2IB0 ----- 2007.05.29 - 19:47:54GMT
-----
We'd be sacrificing a lot of bandwidth at startup, but eventually we should
reach full speed... I guess it partly depends on how long we expect nodes to
stay up.
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