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+=successfulChkFetchBytesReceivedAverage.c
> > > > > >ur re nt Va lu
> > > > > > e()+successfulChkInsertBytesReceivedAverage.currentValue(); //
> > > > > > 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.
----- Anonymous at o9_0DTuZniSf_+oDmRsonByWxsI ----- 2007.05.25 -
11:57:46GMT -----
As far as I see, the tokens should be transferred in timely enough manner, to
keep bursts problem moderate; so majority of them will not be coalesced,
frequently resulting in the folloing overhead for the 6 bytes:
- up to 100 bytes of random padding;
- 50+ bytes FNP headers;
- 8 bytes UDP header;
- 20+ bytes IP header.
Those 150-200 bytes packets, aside being large enough to get noticeable in
number, inavoidably create additional traffic patterns that could be useful
to estimate node's activity with other peers (even if the other peers use
some local connection like Bluetooth/WiFi/LAN which is much more expensive to
monitor remotely/centralized).
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