Messages in this thread | | | Date | Mon, 05 Nov 2007 10:37:48 +0100 | From | Cyrus Massoumi <> | Subject | Re: aim7 -30% regression in 2.6.24-rc1 |
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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@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 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
greetings Cyrus
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