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Date: Wed, 07 Nov 2007 13:30:59 +0800 From: "Zhang, Yanmin" <yanmin_zhang@...ux.intel.com> To: Cyrus Massoumi <cyrusm@....net> Cc: mingo@...e.hu, linux-kernel@...r.kernel.org, a.p.zijlstra@...llo.nl Subject: Re: aim7 -30% regression in 2.6.24-rc1 On Mon, 2007-11-05 at 10:37 +0100, Cyrus Massoumi wrote: > 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 <yanmin_zhang@...ux.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 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? The patch is very big. http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=b5869ce7f68b233ceb81465a7644be0d9a5f3dbb - 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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