Messages in this thread | | | Date | Sun, 1 Aug 2004 07:21:17 -0400 (EDT) | From | Ingo Molnar <> | Subject | Re: [Jackit-devel] Re: Statistical methods for latency profiling |
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On Sun, 1 Aug 2004, Lee Revell wrote:
> So stressing the filesystem moves the center to the right a bit, from > 6-7 to 9-10, and *drastically* lengthens the 'tail'.
basically each codepath has a typical latency distribution, and when a workload uses multiple codepaths then the latencies get intermixed almost linearly.
> These numbers suggest to me that a lot of the latencies from 47 usecs > and up are caused by one code path, because they are so uniformly > distributed over the upper part of the histogram. The prime suspect of > course being the ide io completions. I tested this theory by lowering > max_sectors_kb from 64 to 32:
> These numbers all point to the ide sg completion code as the only thing > on the system generating latencies over ~42 usecs.
yep, that's a fair assumption. Once the IO-APIC irq-redirection problems are solved i'll try to further thread the IDE completion IRQ to remove that ~100 usecs latency.
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