Messages in this thread |  | | | Date | Sun, 21 Aug 2005 13:21:41 -0700 (PDT) | | From | Danial Thom <> | | Subject | Re: 2.6.12 Performance problems |
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--- Jesper Juhl <jesper.juhl@gmail.com> wrote: > On 8/21/05, Jesper Juhl <jesper.juhl@gmail.com> > wrote: > > On 8/21/05, Danial Thom > <danial_thom@yahoo.com> wrote: > > > > > > > Ok, well you'll have to explain this one: > > > > > > "Low latency comes at the cost of decreased > > > throughput - can't have both" > > > > > > Seems to be a bit backwards. Threading the > kernel > > > adds latency, so its the additional latency > in > > > the kernel that causes the drop in > throughput. Do > > > you mean that kernel performance has been > > > sacrificed in order to be able to service > other > > > threads more quickly, even when there are > no > > > other threads to be serviced? > > > > > > > Ok, let me start with the way HZ influences > things. > > > [snip] > > A small followup. > > I'm not saying that the value of HZ or your > preempt setting (whatever > it may be) is definately the cause of your > problem. All I'm saying is > that it might be a contributing factor, so it's > probably something > that's worth a little bit of time testing. > > In many cases people running a server on > resonably new hardware with > HZ=1000 and full preempt won't even notice, but > that's depending on > the load on the server and what jobs it has. > For some tasks it > matters, for some the differences in > performance is negligible. > > You problem could very well be something else > entirely, but try a > kernel build with PREEMPT_NONE and HZ=100 and > see if it makes a big > difference (or if that's your current config, > then try the opposite, > HZ=1000 and PREEMPT). If it does make a > difference, then that's a > valuable piece of information to report on the > list. If it turns out > it makes next to no difference at all, then > that as well is relevant > information as then people will know that HZ & > preempt is not the > cause and can focus on finding the problem > elsewhere. > Yes. Hz isn't going to make much difference on a 2.0Ghz opteron, but I can see how premption can cause packet loss. Shouldn't packet processing be the highest priority process? It seems pointless to "keep the audio buffers full" if you're dropping packets as a result.
Also some clown typing on the keyboard shouldn't cause packet loss. Trading network integrity for snappy responsiveness is a bad trade.
Danial
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