From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f200.google.com (mail-pf0-f200.google.com [209.85.192.200]) by kanga.kvack.org (Postfix) with ESMTP id 3C0406B025F for ; Tue, 8 Aug 2017 23:00:10 -0400 (EDT) Received: by mail-pf0-f200.google.com with SMTP id z3so50725172pfk.4 for ; Tue, 08 Aug 2017 20:00:10 -0700 (PDT) Received: from mga14.intel.com (mga14.intel.com. [192.55.52.115]) by mx.google.com with ESMTPS id a100si2014530pli.530.2017.08.08.20.00.08 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 08 Aug 2017 20:00:08 -0700 (PDT) Date: Wed, 9 Aug 2017 10:59:02 +0800 From: Ye Xiaolong Subject: Re: [lkp-robot] [mm] 7674270022: will-it-scale.per_process_ops -19.3% regression Message-ID: <20170809025902.GA17616@yexl-desktop> References: <20170802000818.4760-7-namit@vmware.com> <20170808011923.GE25554@yexl-desktop> <20170808022830.GA28570@bbox> <93CA4B47-95C2-43A2-8E92-B142CAB1DAF7@gmail.com> <970B5DC5-BFC2-461E-AC46-F71B3691D301@gmail.com> <20170808080821.GA31730@bbox> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20170808080821.GA31730@bbox> Sender: owner-linux-mm@kvack.org List-ID: To: Minchan Kim Cc: Nadav Amit , "open list:MEMORY MANAGEMENT" , LKML , Andrew Morton , Ingo Molnar , Russell King , Tony Luck , Martin Schwidefsky , "David S. Miller" , Heiko Carstens , Yoshinori Sato , Jeff Dike , linux-arch@vger.kernel.org, lkp@01.org On 08/08, Minchan Kim wrote: >On Mon, Aug 07, 2017 at 10:51:00PM -0700, Nadav Amit wrote: >> Nadav Amit wrote: >> >> > Minchan Kim 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 >> > pagea??. 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, Ia??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 A+- 3% -2% 1257 A+- 3% -6% 1207 vmstat.system.cs 2702 A+- 18% 11% 3002 A+- 19% 17% 3156 A+- 18% numa-vmstat.node0.nr_mapped 10765 A+- 18% 11% 11964 A+- 19% 17% 12588 A+- 18% numa-meminfo.node0.Mapped 0.00 A+- 47% -40% 0.00 A+- 45% -84% 0.00 A+- 42% mpstat.cpu.soft% Thanks, Xiaolong >>From 83012114c9cd9304f0d55d899bb4b9329d0e22ac Mon Sep 17 00:00:00 2001 >From: Minchan Kim >Date: Tue, 8 Aug 2017 17:05:19 +0900 >Subject: [PATCH] mm: decrease tlb flush pending count in tlb_finish_mmu > >The tlb pending count increased by tlb_gather_mmu should be decreased >at tlb_finish_mmu. Otherwise, A lot of TLB happens which makes >performance regression. > >Signed-off-by: Minchan Kim >--- > mm/memory.c | 1 + > 1 file changed, 1 insertion(+) > >diff --git a/mm/memory.c b/mm/memory.c >index 34b1fcb829e4..ad2617552f55 100644 >--- a/mm/memory.c >+++ b/mm/memory.c >@@ -423,6 +423,7 @@ void tlb_finish_mmu(struct mmu_gather *tlb, > bool force = mm_tlb_flush_nested(tlb->mm); > > arch_tlb_finish_mmu(tlb, start, end, force); >+ dec_tlb_flush_pending(tlb->mm); > } > > /* >-- >2.7.4 > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org