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 X-Spam-Level: X-Spam-Status: No, score=-10.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D0843C43381 for ; Sat, 16 Jan 2021 17:17:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BA5D620732 for ; Sat, 16 Jan 2021 17:17:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727243AbhAPRFp (ORCPT ); Sat, 16 Jan 2021 12:05:45 -0500 Received: from mga07.intel.com ([134.134.136.100]:19016 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726083AbhAPQ3A (ORCPT ); Sat, 16 Jan 2021 11:29:00 -0500 IronPort-SDR: KlgH7GwjqT4pmDd3Kj6KYtdA7hbyJg1YYV58kjW6wwFOSLy1IgCCh5+XxzhVUlxlemLkrnsRdB cRkAknSav2TQ== X-IronPort-AV: E=McAfee;i="6000,8403,9866"; a="242744366" X-IronPort-AV: E=Sophos;i="5.79,352,1602572400"; d="scan'208";a="242744366" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by orsmga105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 16 Jan 2021 08:09:25 -0800 IronPort-SDR: OCdPPhYfcD5rrxocnafjPCYUr7GHV/KWqUcFHtmcFC8JoKo/qhJSp/lwAPrV9MAw53GxT0ejwF Lb6/wBkernwg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.79,352,1602572400"; d="scan'208";a="354683879" Received: from shbuild999.sh.intel.com (HELO localhost) ([10.239.147.98]) by fmsmga008.fm.intel.com with ESMTP; 16 Jan 2021 08:09:22 -0800 Date: Sun, 17 Jan 2021 00:09:21 +0800 From: Feng Tang To: "Paul E. McKenney" Cc: Borislav Petkov , kernel test robot , Jonathan Lemon , Tony Luck , LKML , x86@kernel.org, lkp@lists.01.org, lkp@intel.com, ying.huang@intel.com, zhengjun.xing@intel.com Subject: Re: [x86/mce] 7bb39313cd: netperf.Throughput_tps -4.5% regression Message-ID: <20210116160921.GA101665@shbuild999.sh.intel.com> References: <20210112142109.GE30747@xsang-OptiPlex-9020> <20210112141438.GF13086@zn.tnic> <20210116035251.GB29609@shbuild999.sh.intel.com> <20210116153413.GP2743@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210116153413.GP2743@paulmck-ThinkPad-P72> User-Agent: Mutt/1.5.24 (2015-08-30) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jan 16, 2021 at 07:34:26AM -0800, Paul E. McKenney wrote: > On Sat, Jan 16, 2021 at 11:52:51AM +0800, Feng Tang wrote: > > Hi Boris, > > > > On Tue, Jan 12, 2021 at 03:14:38PM +0100, Borislav Petkov wrote: > > > On Tue, Jan 12, 2021 at 10:21:09PM +0800, kernel test robot wrote: > > > > > > > > Greeting, > > > > > > > > FYI, we noticed a -4.5% regression of netperf.Throughput_tps due to commit: > > > > > > > > > > > > commit: 7bb39313cd6239e7eb95198950a02b4ad2a08316 ("x86/mce: Make mce_timed_out() identify holdout CPUs") > > > > https://git.kernel.org/cgit/linux/kernel/git/tip/tip.git ras/core > > > > > > > > > > > > in testcase: netperf > > > > on test machine: 192 threads Intel(R) Xeon(R) Platinum 9242 CPU @ 2.30GHz with 192G memory > > > > with following parameters: > > > > > > > > ip: ipv4 > > > > runtime: 300s > > > > nr_threads: 16 > > > > cluster: cs-localhost > > > > test: TCP_CRR > > > > cpufreq_governor: performance > > > > ucode: 0x5003003 > > > > > > > > test-description: Netperf is a benchmark that can be use to measure various aspect of networking performance. > > > > test-url: http://www.netperf.org/netperf/ > > > > > > I'm very very sceptical this thing benchmarks #MC exception handler > > > performance. Because the code this patch adds gets run only during a MCE > > > exception. > > > > > > So unless I'm missing something obvious please check your setup. > > > > We've tracked some similar strange kernel performance changes, like > > another mce related one [1]. For many of them, the root cause is > > the patch changes the code or data alignment/address of other > > components, as could be seen from System.map file. > > > > We added debug patch trying to force data sections of each .o be > > aligned (isolating components), and run the test 3 times, and > > the regression is gone. > > > > %stddev %change %stddev > > \ | \ > > 263059 -0.2% 262523 netperf.Throughput_total_tps > > 16441 -0.2% 16407 netperf.Throughput_tps > > > > So the -4.5% is likely to be caused by data address change. > > > > But still there is something I don't understand, that the patch > > introduces a new cpumask 'mce_missing_cpus', which is 1024B, and > > from the System.map, all data following it get a 1024B offset, > > without changing the cacheline alignment situation. > > > > 2 original system map files are attached in case people want > > to check. > > > > [1]. https://lore.kernel.org/lkml/20200425114414.GU26573@shao2-debian/ > > One possibility is that the data-address changes put more stress on the > TLB, for example, if that region of memory is not covered by a huge > TLB entry. If this is the case, is there a convenient way to define > mce_missing_cpus so as to get it out of the way? Yes! I also tried some experiment for dTLB, by adding 3 more cpumask_t right after 'mce_missing_cpus', so that the total offset will be 4KB. I expected the regression could be gone, but it turns out to have a +2.4% improvement. 16741 -4.5% 15980 +2.4% 17149 netperf.Throughput_tps Which is still kind of out of our control :) Thanks, Feng > Thanx, Paul