Messages in this thread | | | Subject | Re: [LKP] Re: [mm/gup] a308c71bf1: stress-ng.vm-splice.ops_per_sec -95.6% regression | From | Xing Zhengjun <> | Date | Thu, 5 Nov 2020 16:28:54 +0800 |
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On 11/5/2020 2:29 AM, Linus Torvalds wrote: > On Mon, Nov 2, 2020 at 1:15 AM kernel test robot <rong.a.chen@intel.com> wrote: >> >> Greeting, >> >> FYI, we noticed a -95.6% regression of stress-ng.vm-splice.ops_per_sec due to commit: >> >> commit: a308c71bf1e6e19cc2e4ced31853ee0fc7cb439a ("mm/gup: Remove enfornced COW mechanism") >> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master > > Note that this is just the reverse of the previous 2000% improvement > reported by the test robot here: > > https://lore.kernel.org/lkml/20200611040453.GK12456@shao2-debian/ > > and the explanation seems to remain the same: > > https://lore.kernel.org/lkml/CAG48ez1v1b4X5LgFya6nvi33-TWwqna_dc5jGFVosqQhdn_Nkg@mail.gmail.com/ > > IOW, this is testing a special case (zero page lookup) that the "force > COW" patches happened to turn into a regular case (COW creating a > regular page from the zero page). > > The question is whether we should care about the zero page for gup_fast lookup. > > If we do care, then the proper fix is likely simply to allow the zero > page in fast-gup, the same way we already do in slow-gup. > > ENTIRELY UNTESTED PATCH ATTACHED. > > Rong - mind testing this? I don't think the zero-page _should_ be > something that real loads care about, but hey, maybe people do want to > do things like splice zeroes very efficiently..
I test the patch, the regression still existed.
========================================================================================= tbox_group/testcase/rootfs/kconfig/compiler/nr_threads/disk/testtime/class/cpufreq_governor/ucode: lkp-csl-2sp5/stress-ng/debian-10.4-x86_64-20200603.cgz/x86_64-rhel-8.3/gcc-9/100%/1HDD/30s/pipe/performance/0x5002f01
commit: 1a0cf26323c80e2f1c58fc04f15686de61bfab0c a308c71bf1e6e19cc2e4ced31853ee0fc7cb439a da5ba9980aa2211c1e2a89fc814abab2fea6f69d (debug patch)
1a0cf26323c80e2f a308c71bf1e6e19cc2e4ced3185 da5ba9980aa2211c1e2a89fc814 ---------------- --------------------------- --------------------------- %stddev %change %stddev %change %stddev \ | \ | \ 3.406e+09 -95.6% 1.49e+08 -96.4% 1.213e+08 stress-ng.vm-splice.ops 1.135e+08 -95.6% 4965911 -96.4% 4041777 stress-ng.vm-splice.ops_per_sec
> > And note the "untested" part of the patch. It _looks_ fairly obvious, > but maybe I'm missing something. > > Linus > > > _______________________________________________ > LKP mailing list -- lkp@lists.01.org > To unsubscribe send an email to lkp-leave@lists.01.org >
-- Zhengjun Xing
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