Messages in this thread | | | From | Valentin Schneider <> | Subject | Re: [REGRESSION] 5-10% increase in IO latencies with nohz balance patch | Date | Fri, 03 Dec 2021 12:03:27 +0000 |
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On 30/11/21 00:26, Valentin Schneider wrote: > On 29/11/21 14:49, Josef Bacik wrote: >> On Mon, Nov 29, 2021 at 06:31:17PM +0000, Valentin Schneider wrote: >>> On 29/11/21 13:15, Josef Bacik wrote: >>> > On Mon, Nov 29, 2021 at 06:03:24PM +0000, Valentin Schneider wrote: >>> >> Would you happen to have execution traces by any chance? If not I should be >>> >> able to get one out of that fsperf thingie. >>> >> >>> > >>> > I don't, if you want to tell me how I can do it right now. I've disabled >>> > everything on this box for now so it's literally just sitting there waiting to >>> > have things done to it. Thanks, >>> > >>> >>> I see you have Ftrace enabled in your config, so that ought to do it: >>> >>> trace-cmd record -e 'sched:*' -e 'cpu_idle' $your_test_cmd >>> >> >> http://toxicpanda.com/performance/trace.dat >> >> it's like 16mib. Enjoy, >> > > Neat, thanks! > > Runqueue depth seems to be very rarely greater than 1, tasks with ~1ms > runtime and lots of sleeping (also bursty kworker activity with activations > of tens of µs), and some cores (Internet tells me that Xeon Bronze 3204 > doesn't have SMT) spend most of their time idling. Not the most apocalyptic > task placement vs ILB selection, but the task activation patterns roughly > look like what I was thinking of - there might be hope for me yet. > > I'll continue the headscratching after tomorrow's round of thinking juice. >
Could you give the 4 top patches, i.e. those above 8c92606ab810 ("sched/cpuacct: Make user/system times in cpuacct.stat more precise") a try?
https://git.gitlab.arm.com/linux-arm/linux-vs.git -b mainline/sched/nohz-next-update-regression
I gave that a quick test on the platform that caused me to write the patch you bisected and looks like it didn't break the original fix. If the above counter-measures aren't sufficient, I'll have to go poke at your reproducers...
>> Josef
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