Messages in this thread | | | Subject | Re: [lkp-robot] [mm] 7674270022: will-it-scale.per_process_ops -19.3% regression | From | Nadav Amit <> | Date | Mon, 7 Aug 2017 21:23:34 -0700 |
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Minchan Kim <minchan@kernel.org> wrote:
> Hi, > > On Tue, Aug 08, 2017 at 09:19:23AM +0800, kernel test robot wrote: >> Greeting, >> >> FYI, we noticed a -19.3% regression of will-it-scale.per_process_ops due to commit: >> >> >> commit: 76742700225cad9df49f05399381ac3f1ec3dc60 ("mm: fix MADV_[FREE|DONTNEED] TLB flush miss problem") >> url: https://github.com/0day-ci/linux/commits/Nadav-Amit/mm-migrate-prevent-racy-access-to-tlb_flush_pending/20170802-205715 >> >> >> in testcase: will-it-scale >> on test machine: 88 threads Intel(R) Xeon(R) CPU E5-2699 v4 @ 2.20GHz with 64G memory >> with following parameters: >> >> nr_task: 16 >> mode: process >> test: brk1 >> cpufreq_governor: performance >> >> test-description: Will It Scale takes a testcase and runs it from 1 through to n parallel copies to see if the testcase will scale. It builds both a process and threads based test in order to see any differences between the two. >> test-url: https://github.com/antonblanchard/will-it-scale > > Thanks for the report. > Could you explain what kinds of workload you are testing? > > Does it calls frequently madvise(MADV_DONTNEED) in parallel on multiple > threads?
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.
Nadav
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