Thus spake Roger Dingledine (arma@xxxxxxx): > On Wed, Jul 18, 2007 at 02:18:56AM -0700, Mike Perry wrote: > > Why does it matter if routers are CPU or network bound? From the Tor > > network routing point of view, it shouldn't matter, capacity is > > capacity. If it is a problem for node operators, they limit their > > bandwidth in the config, problem solved. If they don't, then they just > > run at 100% CPU, and Tor should still properly report their observed > > bandwidth rate (unless they lie, but again, that is a another, > > orthogonal matter). > > Well, the problem is that Tor in fact doesn't properly report capacity at > the extremes. Our measure of capacity is the most you've seen yourself > burst in the past day -- it pretty much assumes that the pipe and other > resources you have are static throughout the day. > > So if you somehow managed to push a lot briefly but you're too busy to > handle that level of traffic sustained, then you've overadvertised. Again, this happens both with network load and CPU load. In fact, I think the network load capacity differences are far more extreme and far more common. On my box, Tor uses 10% CPU, but is constantly prioritized below regular traffic, which is bursty and very irregular. My node is also below the 1.5Mbyte/sec barrier, so it does not help even out this problem for me, nor most others who share Tor with normal traffic. > Putting a cap on advertised bandwidth when load balancing is a crude way > to account for this. Making our bandwidth estimate more complex may also > work, but then we have to figure out what's better. :) If it has to be fixed one place, it is probably best done by not advertising burst traffic. That problem is independent of this patch, though, IMO. -- Mike Perry Mad Computer Scientist fscked.org evil labs
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