Messages in this thread | | | Date | Tue, 18 Sep 2007 05:45:15 -0400 | From | "Rob Hussey" <> | Subject | Re: Scheduler benchmarks - a follow-up |
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On 9/18/07, Ingo Molnar <mingo@elte.hu> wrote: > > * Rob Hussey <robjhussey@gmail.com> wrote: > > > The obligatory graphs: > > http://www.healthcarelinen.com/misc/benchmarks/BOUND_NOPREEMPT_lat_ctx_benchmark.png > > http://www.healthcarelinen.com/misc/benchmarks/BOUND_NOPREEMPT_hackbench_benchmark.png > > http://www.healthcarelinen.com/misc/benchmarks/BOUND_NOPREEMPT_pipe-test_benchmark.png > > btw., it's likely that if you turn off CONFIG_PREEMPT for .21 and for > .22-ck1 they'll improve a bit too - so it's not fair to put the .23 > !PREEMPT numbers on the graph as the PREEMPT numbers of the other > kernels. (it shows the .23 scheduler being faster than it really is) >
The graphs are really just to show where the new numbers fit in. Plus, I was too lazy to run all the numbers again.
> > A cursory glance suggests that performance wrt lat_ctx and hackbench > > has increased (lower numbers), but degraded quite a lot for pipe-test. > > The numbers for pipe-test are extremely stable though, while the > > numbers for hackbench are more erratic (which isn't saying much since > > the original numbers gave nearly a straight line). I'm still willing > > to try out any more ideas. > > the pipe-test behavior looks like an outlier. !PREEMPT only removes code > (which makes the code faster), so this could be a cache layout artifact. > (or perhaps we preempt at a different point which is disadvantageous to > caching?) Pipe-test is equivalent to "lat_ctx -s 0 2" so if there was a > genuine slowdown it would show up in the lat_ctx graph - but the graph > shows a speedup. >
Interestingly, every set of lat_ctx -s 0 2 numbers I run on the !PREEMPT kernel are on average higher than with PREEMPT (around 2.84 for !PREEMPT and 2.4 for PREEMPT). Anything higher than around 2 or 3 (such as lat_ctx -s 0 8) gives lower average numbers for !PREEMPT.
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