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    SubjectRe: Performance changes between 2.6.13 and 2.6.23
    On Tue, Mar 25, 2008 at 5:34 AM, Sanders, Rob M. <> wrote:
    > Hello all,
    > I've been lurking on the digest for some time (don't want to receive full lkml traffic at work) and saw the
    > posts about Wine performance regressions in 2.6.24. Some of what I saw there, particularly Andi Kleen's
    > responses, mirror something that I see on my box at home. I had emailed Andi directly since I only read the
    > digest, and I'm posting this here at his suggestion. Please CC: with any replies, as I'm only
    > getting the lkml digest.
    > I'm running on a dual 2GHZ G5 Powermac w/2GB ram. I recently upgraded from YDL4.0.91 (2.6.13 kernel) to
    > YDL6 (2.6.23 kernel) and noticed that the overall performance of the box seems more sluggish after the upgrade.
    > Of more particular concern, the main application that I build has seen a 4-5X slowdown in performance. Under
    > YDL4.0.91 I could process roughly 1e8 data points in ~2 seconds, and under YDL6.0 I now process 1e8 data points

    So, two processors, and multiple processes passing data back and
    forth. Key point seems to be:

    > in ~8 seconds. Total CPU loading (from top) is about 5%, under both systems. The application spawns multiple
    > processes and uses semaphores and shared memory to move data between the processes. When I use 'vmstat 3' the
    > single biggest difference I see between YDL4.0.91 and YDL6 is that the YDL4.0.91 system is the YDL4.0.91 system is
    > context switching about 7000 per interval, whereas the YDl6 system is context switching about 1200 times per interval.

    Many more context switches per second, so a lot less work is getting
    done each time.

    > I've been talking somewhat with Owen Stampflee (works for the distro maker, TSS) and have rebuilt the kernel on
    > the 2.6 box removing some of the things that I don't need on my box (cell support, etc). There did seem (subjectively)
    > to be a slight improvement after that. When I get some more time to play at home I'm going to take the 2.6.13 .config
    > I use and build a 2.6.23 kernal using 'make oldconfig' and try to figure if it is a config issues.
    > I realize that going from 2.6.13 to 2.6.23 is a *huge* change, and that the problems may not be tied to the kernel
    > but to other things, but are there any other suggestions folks have for finding the cause of the performance slowdow

    A lot has changed between 2.6.23 and current mainline as well.
    Particularly in the scheduler, which I suspect is the issue for your
    test. If possible, could you try a 2.6.25-rc-latest kernel, both
    before and after an "echo 5 > /proc/sys/kernel/sched_features" and see
    if that makes any difference?

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