From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 73229C433F5 for ; Sat, 15 Jan 2022 00:07:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230263AbiAOAHw (ORCPT ); Fri, 14 Jan 2022 19:07:52 -0500 Received: from out01.mta.xmission.com ([166.70.13.231]:40294 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229509AbiAOAHv (ORCPT ); Fri, 14 Jan 2022 19:07:51 -0500 Received: from in02.mta.xmission.com ([166.70.13.52]:59370) by out01.mta.xmission.com with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1n8Wbk-00DMyZ-OK; Fri, 14 Jan 2022 17:07:48 -0700 Received: from ip68-110-24-146.om.om.cox.net ([68.110.24.146]:35432 helo=email.froward.int.ebiederm.org.xmission.com) by in02.mta.xmission.com with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1n8Wbi-007vuP-E5; Fri, 14 Jan 2022 17:07:48 -0700 From: "Eric W. Biederman" To: Oliver Sang Cc: Alexey Gladkov , Gleb Fotengauer-Malinovskiy , LKML , lkp@lists.01.org, lkp@intel.com, ying.huang@intel.com, feng.tang@intel.com, zhengjun.xing@linux.intel.com, fengwei.yin@intel.com References: <20220112134211.GA10024@xsang-OptiPlex-9020> <874k68pyag.fsf@email.froward.int.ebiederm.org> <20220113021704.GA18396@xsang-OptiPlex-9020> Date: Fri, 14 Jan 2022 18:07:39 -0600 In-Reply-To: <20220113021704.GA18396@xsang-OptiPlex-9020> (Oliver Sang's message of "Thu, 13 Jan 2022 10:17:04 +0800") Message-ID: <87y23hkgj8.fsf@email.froward.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1n8Wbi-007vuP-E5;;;mid=<87y23hkgj8.fsf@email.froward.int.ebiederm.org>;;;hst=in02.mta.xmission.com;;;ip=68.110.24.146;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1/McjTzzKV4lUmYllqnij+TV0vdFPRhcvc= X-SA-Exim-Connect-IP: 68.110.24.146 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [ucounts] 59ec71575a: will-it-scale.per_process_ops -10.3% regression X-SA-Exim-Version: 4.2.1 (built Sat, 08 Feb 2020 21:53:50 +0000) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Oliver Sang writes: > Hi Eric, > > On Wed, Jan 12, 2022 at 01:08:23PM -0600, Eric W. Biederman wrote: >> kernel test robot writes: >> >> > Greeting, >> > >> > FYI, we noticed a -10.3% regression of will-it-scale.per_process_ops due to commit: >> >> >> I am having a bit of a challenge reading this report. Does the -10.3% >> mean that will-it-scale.per_process_ops is performing 70873 operations >> per second instead of 78995 aka -10.3% fewer operations per second? > > yes > >> >> The per-profile.self-cycles-pp.do_dec_rlimits_put_ucounts now takes +2.6 >> more cycles, and perf-profile.self.cycles.pp.inc_rlimit_get_ucounts now >> takes +3.8 more cycles. >> >> Which if I read this correctly is a regression report about two >> functions taking 3 or 4 cycles more after the code was rearranged inside >> of them. >> >> Is that correct? Is this a regression report saying those two functions >> are taking a few cycles more which leads to >> will-it-scale.per_process_ops not being able to perform as many >> operations per second? > > yes > >> >> Given the change in the commit mentioned I think this is all down to a >> bug fix causing the code to be rearranged and a compiler optimizations. >> >> I don't see much room to do anything about this. > > got it. this is a bug fix. Thanks for explanation! The big surprise is that we haven't seen performance regressions up until this point as the ucount rlimit work was merged. Unless we can spot something very silly that the compiler is doing with code generation (and those 3 or 4 cycles suggests it is possible the compiler is being silly) it is going to take some reorganizing to improve the performance. Eric