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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 688C0C433DF for ; Mon, 24 Aug 2020 15:15:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3D76B2074D for ; Mon, 24 Aug 2020 15:15:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726599AbgHXPPj (ORCPT ); Mon, 24 Aug 2020 11:15:39 -0400 Received: from mx2.suse.de ([195.135.220.15]:42298 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725946AbgHXPOZ (ORCPT ); Mon, 24 Aug 2020 11:14:25 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id AA00AABCC; Mon, 24 Aug 2020 15:14:53 +0000 (UTC) Date: Mon, 24 Aug 2020 17:14:25 +0200 From: Borislav Petkov To: Feng Tang Cc: "Luck, Tony" , kernel test robot , LKML , lkp@lists.01.org, Mel Gorman Subject: Re: [LKP] Re: [x86/mce] 1de08dccd3: will-it-scale.per_process_ops -14.1% regression Message-ID: <20200824151425.GF4794@zn.tnic> References: <20200425114414.GU26573@shao2-debian> <20200425130136.GA28245@zn.tnic> <20200818082943.GA65567@shbuild999.sh.intel.com> <20200818200654.GA21494@agluck-desk2.amr.corp.intel.com> <20200819020437.GA2605@shbuild999.sh.intel.com> <20200821020259.GA90000@shbuild999.sh.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200821020259.GA90000@shbuild999.sh.intel.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 21, 2020 at 10:02:59AM +0800, Feng Tang wrote: > 1de08dccd383 x86/mce: Add a struct mce.kflags field > 9554bfe403bd x86/mce: Convert the CEC to use the MCE notifier > > And strange thing is after using gcc9 and debian10 rootfs, with same commits > the regression turns to a improvement, How so? > though the trend keeps, that if we > changes the kflags from __u64 to __u32, the performance will be no change. > > Following is the comparing of regression, I also attached the perf-profile > for old and new commit (let me know if you need more data) > > > 9554bfe403bdfc08 1de08dccd383482a3e88845d355 > ---------------- --------------------------- > %stddev %change %stddev > \ | \ > 192362 -15.1% 163343 will-it-scale.287.processes > 0.91 +0.2% 0.92 will-it-scale.287.processes_idle > 669.67 -15.1% 568.50 will-it-scale.per_process_ops This is the data from your previous measurement: 9554bfe403bdfc08 1de08dccd383482a3e88845d355 ---------------- --------------------------- %stddev %change %stddev \ | \ 668.00 -14.1% 573.75 will-it-scale.per_process_ops If I'm reading it correctly, commit 1de08dccd383 ("x86/mce: Add a struct mce.kflags field") is still the slower one vs 9554bfe403bd ("x86/mce: Convert the CEC to use the MCE notifier") Or am I misreading it? In any case, this really looks like what Tony said: this enlargement of struct mce pushes some variable into a cacheline-misaligned placement, causing it to bounce. The $ 10^6 question is, which variable is that... -- Regards/Gruss, Boris. SUSE Software Solutions Germany GmbH, GF: Felix Imendörffer, HRB 36809, AG Nürnberg