Messages in this thread | | | Date | Tue, 15 Dec 2020 09:37:32 +0100 | From | Peter Zijlstra <> | Subject | Re: [LKP] Re: [sched/hotplug] 2558aacff8: will-it-scale.per_thread_ops -1.6% regression |
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On Tue, Dec 15, 2020 at 01:35:46PM +0800, Xing Zhengjun wrote: > On 12/11/2020 12:14 AM, Peter Zijlstra wrote: > > On Thu, Dec 10, 2020 at 04:18:59PM +0800, kernel test robot wrote: > > > FYI, we noticed a -1.6% regression of will-it-scale.per_thread_ops due to commit: > > > commit: 2558aacff8586699bcd248b406febb28b0a25de2 ("sched/hotplug: Ensure only per-cpu kthreads run during hotplug") > > > > Mooo, weird but whatever. Does the below help at all? > > I test the patch
Thanks!
> , the regression reduced to -0.6%. > > ========================================================================================= > tbox_group/testcase/rootfs/kconfig/compiler/nr_task/mode/test/cpufreq_governor/ucode: > > lkp-cpl-4sp1/will-it-scale/debian-10.4-x86_64-20200603.cgz/x86_64-rhel-8.3/gcc-9/100%/thread/sched_yield/performance/0x700001e > > commit: > 565790d28b1e33ee2f77bad5348b99f6dfc366fd > 2558aacff8586699bcd248b406febb28b0a25de2 > 4b26139b8db627a55043183614a32b0aba799d27 (this test patch) > > 565790d28b1e33ee 2558aacff8586699bcd248b406f 4b26139b8db627a55043183614a > ---------------- --------------------------- --------------------------- > %stddev %change %stddev %change %stddev > \ | \ | \ > 4.011e+08 -1.6% 3.945e+08 -0.6% 3.989e+08 will-it-scale.144.threads > 2785455 -1.6% 2739520 -0.6% 2769967 will-it-scale.per_thread_ops > 4.011e+08 -1.6% 3.945e+08 -0.6% 3.989e+08 will-it-scale.workload
Well, that's better. But I'm rather confused now, because with this new patch, the actual hot paths are identical, so I've no idea what is actually causing the regression :/
The above numbers don't seem to have variance, how sure are we the results are stable? The thing is, when I tried reproducing this locally, I was mostly looking at noise.
> > --- > > kernel/sched/core.c | 40 +++++++++++++++------------------------- > > kernel/sched/sched.h | 13 +++++-------- > > 2 files changed, 20 insertions(+), 33 deletions(-)
Anyway, let me queue this in sched/urgent, it's simpler code and has less regression.
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