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Message-ID: <20070918064046.GD5138@elte.hu> Date: Tue, 18 Sep 2007 08:40:46 +0200 From: Ingo Molnar <mingo@...e.hu> To: Rob Hussey <robjhussey@...il.com> Cc: linux-kernel@...r.kernel.org, ck@....kolivas.org Subject: Re: Scheduler benchmarks - a follow-up * Rob Hussey <robjhussey@...il.com> wrote: > 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. pipe-test is a very stable workload, and is thus quite sensitive to the associativity of the CPU cache. Even killing the task and repeating the same test isnt enough to get rid of the systematic skew that this can cause. I've seen divergence of up to 10% in pipe-test. One way to test it is to run pipe-test, then to stop it, then to "ssh localhost" (this in itself uses up a couple of pipe objects and file objects and changes the cache layout picture), then run pipe-test again, then again "ssh localhost", etc. Via this trick one can often see cache-layout artifacts. How much 'skew' does pipe-test have on your system if you try this manually? Ingo - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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