Re: [lkp-robot] [mm] 7674270022: will-it-scale.per_process_ops -19.3% regression

Minchan Kim
2017-08-10T04:20:44Z

On Wed, Aug 09, 2017 at 09:14:50PM -0700, Nadav Amit wrote:

Hi Nadav,

< snip >

> >>>>> According to the description it is "testcase:brk increase/decrease of one
> >>>>> page”. According to the mode it spawns multiple processes, not threads.
> >>>>>
> >>>>> Since a single page is unmapped each time, and the iTLB-loads increase
> >>>>> dramatically, I would suspect that for some reason a full TLB flush is
> >>>>> caused during do_munmap().
> >>>>>
> >>>>> If I find some free time, I’ll try to profile the workload - but feel free
> >>>>> to beat me to it.
> >>>>
> >>>> The root-cause appears to be that tlb_finish_mmu() does not call
> >>>> dec_tlb_flush_pending() - as it should. Any chance you can take care of it?
> >>>
> >>> Oops, but with second looking, it seems it's not my fault. ;-)
> >>> https://marc.info/?l=linux-mm&m=150156699114088&w=2
> >>>
> >>> Anyway, thanks for the pointing out.
> >>> xiaolong.ye, could you retest with this fix?
> >>
> >> I've queued tests for 5 times and results show this patch (e8f682574e4 "mm:
> >> decrease tlb flush pending count in tlb_finish_mmu") does help recover the
> >> performance back.
> >>
> >> 378005bdbac0a2ec 76742700225cad9df49f053993 e8f682574e45b6406dadfffeb4
> >> ---------------- -------------------------- --------------------------
> >> %stddev change %stddev change %stddev
> >> \ | \ | \
> >> 3405093 -19% 2747088 -2% 3348752 will-it-scale.per_process_ops
> >> 1280 ± 3% -2% 1257 ± 3% -6% 1207 vmstat.system.cs
> >> 2702 ± 18% 11% 3002 ± 19% 17% 3156 ± 18% numa-vmstat.node0.nr_mapped
> >> 10765 ± 18% 11% 11964 ± 19% 17% 12588 ± 18% numa-meminfo.node0.Mapped
> >> 0.00 ± 47% -40% 0.00 ± 45% -84% 0.00 ± 42% mpstat.cpu.soft%
> >>
> >> Thanks,
> >> Xiaolong
> >
> > Thanks for the testing!
>
> Sorry again for screwing your patch, Minchan.

Never mind! It always happens. :)
In this chance, I really appreciates your insight/testing/cooperation!