Nadav Amit <nadav.amit@xxxxxxxxx> wrote: > Minchan Kim <minchan@xxxxxxxxxx> 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. 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? Having said that it appears that cpumask_any_but() is really inefficient since it does not have an optimization for the case in which small_const_nbits(nbits)==true. When I find some free time, I’ll try to deal with it. Thanks, Nadav