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Date: Thu, 01 Nov 2007 17:34:29 +0800 From: "Zhang, Yanmin" <yanmin_zhang@...ux.intel.com> To: Ingo Molnar <mingo@...e.hu> Cc: LKML <linux-kernel@...r.kernel.org>, Peter Zijlstra <a.p.zijlstra@...llo.nl> Subject: Re: aim7 -30% regression in 2.6.24-rc1 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! -yanmin - 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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