Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751993AbdHHFvJ (ORCPT ); Tue, 8 Aug 2017 01:51:09 -0400 Received: from mail-qt0-f193.google.com ([209.85.216.193]:35621 "EHLO mail-qt0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750777AbdHHFvE (ORCPT ); Tue, 8 Aug 2017 01:51:04 -0400 Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 10.3 \(3273\)) Subject: Re: [lkp-robot] [mm] 7674270022: will-it-scale.per_process_ops -19.3% regression From: Nadav Amit In-Reply-To: <93CA4B47-95C2-43A2-8E92-B142CAB1DAF7@gmail.com> Date: Mon, 7 Aug 2017 22:51:00 -0700 Cc: kernel test robot , "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 Message-Id: <970B5DC5-BFC2-461E-AC46-F71B3691D301@gmail.com> References: <20170802000818.4760-7-namit@vmware.com> <20170808011923.GE25554@yexl-desktop> <20170808022830.GA28570@bbox> <93CA4B47-95C2-43A2-8E92-B142CAB1DAF7@gmail.com> To: Minchan Kim X-Mailer: Apple Mail (2.3273) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by nfs id v785pDF3004333 Content-Length: 2074 Lines: 54 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 > 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