Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: Performance issue since 3.2.6 | Date | Fri, 18 Jan 2013 22:46:32 +0100 |
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On Friday, January 18, 2013 10:24:48 PM Borislav Petkov wrote: > Good description. > > I'm leaving the whole email in for reference, see below: > > On Fri, Jan 18, 2013 at 10:05:41PM +0100, Olivier Doucet wrote: > > Hello, > > > > I think I found a performance issue in kernel. This problem was > > introduced in 3.2.6 and is affecting all version, including 3.7.1 > > (latest tested). > > > > I measured several kernel builds with a homebrew LAMP platform > > benchmark (250 runs, average value kept). > > > > Kernel 3.2.0 was on production so far, and I tried an upgrade to 3.7.1 > > (latest kernel at that time). No software other than the kernel was > > modified. Kernel was built with the same .config file (new options > > left with default value). > > Difference in performance was quite huge : > > Kernel 3.7.1 : ~ 3250 queries / second > > Kernel 3.2.0 : ~ 4300 queries / second > > > > Yes, this is a 25% performance drop ... > > > > To narrow things down, I tested several kernels : > > 3.2.0 to 3.2.5 : OK > > 3.2.6, 3.2.11, 3.2.28, 3.2.36, 3.7.1 : PERFORMANCE DROP > > On faulty kernels, performance drop is always the same. > > > > At this step, I know that bug was introduced in version 3.2.6. I then > > used git bisect (amazing tool btw) to find the faulty commit : > > f51d67a64f32cd81ea8b67ca964fb7cf7e783b2e PM / QoS: CPU C-state > > breakage with PM Qos change > > > > Next test : I used a 3.2.6 and reverted this patch : performance was > > back to normal. > > I also reverted this patch on 3.2.36 (latest 3.2.X), and performance > > was also OK. I was unable to revert this patch on 3.7.1 (structure of > > the source file /include/linux/pm_qos.h changed too heavily). > > > > Kernel was built on a x86_64 platform with binutils 2.19.1 and gcc 4.4.0. > > .config file used : https://gist.github.com/4567342 > > Benchmark was run on a dual CPU INTEL L5630 with 4GB of RAM > > > > What can I do to resolve this problem ? > > Btw, the commit-id you've given is the stable commit-id but this is > still ok, the mainline commit is mentioned in the commit message and is: > > commit d020283dc694c9ec31b410f522252f7a8397e67d > Author: Venkatesh Pallipadi <venki@google.com> > Date: Fri Feb 3 22:22:25 2012 +0100 > > PM / QoS: CPU C-state breakage with PM Qos change > > So, let's invite the parties from the commit to CC, see what they have > to say.
Thanks Boris!
Olivier, may I see the kernel .config file?
Rafael
-- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center.
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