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    SubjectRe: Scheduler benchmarks - a follow-up

    * 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)

    > 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.

    Ingo
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