* Malkus Lindroos <malkus at iki.fi> [2007-08-21 15:51:51]:

> Matthew Toseland wrote:
> > On Tuesday 21 August 2007 00:13, Matthew Toseland wrote:
> >> On Monday 20 August 2007 21:59, Malkus Lindroos wrote:
> >>> Of course it depends on what the ping time is supposed to reflect? At
> >>> least for my nodes it seems to reflect the load of the network the node
> >>> is connected to, not the load of the node or its internet connection.
> >> It's a combination of the round trip time under ideal conditions (<0.2ms 
> >> on 
> > my 
> >> LAN), and the effect of the traffic on the links between the nodes 
> > (including 
> >> rate limiting).
> > 
> > Sorry, not just network load, ping time is highly sensitive to CPU load on 
> > both ends too. This is why it's such a useful metric; we can't easily 
> > directly measure CPU load, and even if we create platform specific hacks, 
> > we'd be fooled by idle-time processes etc.
> 
> OK - so there comes the problem. My node CPU load is only about 5-10%.
> It has clearly idle time, and the maxpingtime is the primary limiter.
> Some connected nodes have lower ping times than others - while many
> nodes have ping times of 3000-4000 ms, some stay at 500. My node also
> has plenty of free bandwidth and its hard disk is not overloaded.
> 
> So in effect, the average ping is reflecting the CPU loads, bandwiths,
> disk usage, etc. of my node + the nodes is connected to. This eliminates
> load distribution among the nodes, as my node does not take more work
> from the overloaded nodes because the overloaded nodes are limiting it.
> When the load of the neighbouring nodes worsens, they also limit my
> nodes ability to take load. I.e. the main problem in the ping times is
> that it is determined not only by my node, but also the nodes that it is
> connected to. In addition, the ping time is determined by a principle of
> the weakest link - the ping time of a node becomes high if only one of
> the nodes is overloaded.
> 
> This also provides a possibility for a denial of service attack against
> the 0.7 network - from the code it is not too difficult for someone
> wishing to impede free speech (or the 0.7 against 0.5 networks) to
> create bogus nodes that report way too high ping times. This would
> severely hurt the 0.7 network from reaching its potential.

Using the median insteed of the mean solves that problem... Moreover
really high ping times are not possible because there is a timeout.

> 
> Because of this, there should at least be an option to disable the use
> of maxpingtimes in the config for now and see if the network would
> become faster.
> 

Again, it's not a problem unless most of your peers are missbehaving...
And as you choose them it's up to you.

NextGen$
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