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    SubjectRe: aim7 -30% regression in 2.6.24-rc1
    Zhang, Yanmin wrote:
    > On Thu, 2007-11-01 at 11:02 +0100, Cyrus Massoumi wrote:
    >> 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 <> 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 ( with 2.6.24-rc1?
    > It looks like you missed my emails.

    Yeah :(

    > Firstly, I reproduced (or just find the same myself :) ) the issue with kernel 2.6.22,
    > 2.6.23-rc and 2.6.23.
    > Ingo wrote a big patch to fix it and the new patch is in 2.6.24-rc1 now.

    That's nice, could you please point me to the commit?

    > Then I retested it with 2.6.24-rc1 on a couple of x86_64 machines. The issue
    > disappeared. You could test it with 2.6.24-rc1.

    Will do!

    >> It
    >> would be nice if you could provide some numbers for 2.6.22, 2.6.23 and
    >> 2.6.24-rc1.
    > Sorry. Intel policy doesn't allow me to publish the numbers because only
    > specific departments in Intel could do that. But I could talk the regression
    > percentage.

    Fair enough :)

    > -yanmin


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