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    SubjectRe: aim7 -30% regression in 2.6.24-rc1
    Zhang, Yanmin wrote:
    > On Wed, 2007-10-31 at 17:57 +0800, Zhang, Yanmin wrote:
    >> On Tue, 2007-10-30 at 16:36 +0800, Zhang, Yanmin wrote:
    >>> On Tue, 2007-10-30 at 08:26 +0100, Ingo Molnar wrote:
    >>>> * Zhang, Yanmin <yanmin_zhang@linux.intel.com> wrote:
    >>>>
    >>>>> sub-bisecting captured patch
    >>>>> 38ad464d410dadceda1563f36bdb0be7fe4c8938(sched: uniform tunings)
    >>>>> caused 20% regression of aim7.
    >>>>>
    >>>>> The last 10% should be also related to sched parameters, such like
    >>>>> sysctl_sched_min_granularity.
    >>>> ah, interesting. Since you have CONFIG_SCHED_DEBUG enabled, could you
    >>>> please try to figure out what the best value for
    >>>> /proc/sys/kernel_sched_latency, /proc/sys/kernel_sched_nr_latency and
    >>>> /proc/sys/kernel_sched_min_granularity is?
    >>>>
    >>>> there's a tuning constraint for kernel_sched_nr_latency:
    >>>>
    >>>> - kernel_sched_nr_latency should always be set to
    >>>> kernel_sched_latency/kernel_sched_min_granularity. (it's not a free
    >>>> tunable)
    >>>>
    >>>> i suspect a good approach would be to double the value of
    >>>> kernel_sched_latency and kernel_sched_nr_latency in each tuning
    >>>> iteration, while keeping kernel_sched_min_granularity unchanged. That
    >>>> will excercise the tuning values of the 2.6.23 kernel as well.
    >>> I followed your idea to test 2.6.24-rc1. The improvement is slow.
    >>> When sched_nr_latency=2560 and sched_latency_ns=640000000, the performance
    >>> is still about 15% less than 2.6.23.
    >> I got the aim7 30% regression on my new upgraded stoakley machine. I found
    >> this mahcine is slower than the old one. Maybe BIOS has issues, or memeory(Might not
    >> be dual-channel?) is slow. So I retested it on the old machine and found on the old
    >> stoakley machine, the regression is about 6%, quite similiar to the regression on tigerton
    >> machine.
    >>
    >> By sched_nr_latency=640 and sched_latency_ns=640000000 on the old stoakley machine,
    >> the regression becomes about 2%. Other latency has more regression.
    >>
    >> On my tulsa machine, by sched_nr_latency=640 and sched_latency_ns=640000000,
    >> the regression becomes less than 1% (The original regression is about 20%).
    > I rerun SPECjbb by ched_nr_latency=640 and sched_latency_ns=640000000. On tigerton,
    > the regression is still more than 40%. On stoakley machine, it becomes worse (26%,
    > original is 9%). I will do more investigation to make sure SPECjbb regression is
    > also casued by the bad default values.
    >
    > We need a smarter method to calculate the best default values for the key tuning
    > parameters.
    >
    > One interesting is sysbench+mysql(readonly) got the same result like 2.6.22 (no
    > regression). Good job!

    Do you mean you couldn't reproduce the regression which was reported
    with 2.6.23 (http://lkml.org/lkml/2007/10/30/53) with 2.6.24-rc1? It
    would be nice if you could provide some numbers for 2.6.22, 2.6.23 and
    2.6.24-rc1.

    > -yanmin

    greetings
    Cyrus

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