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=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 581EEC4361B for ; Tue, 15 Dec 2020 08:38:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 07B1D22286 for ; Tue, 15 Dec 2020 08:38:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727302AbgLOIi3 (ORCPT ); Tue, 15 Dec 2020 03:38:29 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44502 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727116AbgLOIi2 (ORCPT ); Tue, 15 Dec 2020 03:38:28 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 28559C06179C for ; Tue, 15 Dec 2020 00:37:48 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=TC51uqq1p8Gvk7HbcRNA0jHcvsxuvd5APsCIWt526AE=; b=aGm10r7IVXL1/fXK43FKlaSU8H LQzPhd/c+VtzszxRf2uOnIMeeDdTscI1bwkI7d1pmEPQD52JJdZQk2SByV2TC4MVkUX1O05sX8MlK 3lHHC9XdVDepTIdiFaWw/Tpnwkm7P7gtck9JuFmA8mfpTzJtHrlli9iqwDeXfaICmCrM3mCXojeyw z6P2IE04PiIKeTOgfSnBX4X/tdCitARCeAuAsexgm+bVDfPhlMsdYO96ukXx/eitdxig1HxQ3It9Q 8pshYx6zbzVTW6RK+OwWBiMOp8ePpaaiy/lG0qKkvmhD7vd08sHtsoPFtTNqAJuVtaVO7cVEDnQUV vfbkn5tg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kp5pu-0003h8-GT; Tue, 15 Dec 2020 08:37:34 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id E1F75302753; Tue, 15 Dec 2020 09:37:32 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id D007120218DB9; Tue, 15 Dec 2020 09:37:32 +0100 (CET) Date: Tue, 15 Dec 2020 09:37:32 +0100 From: Peter Zijlstra To: Xing Zhengjun Cc: kernel test robot , Valentin Schneider , Daniel Bristot de Oliveira , LKML , x86@kernel.org, lkp@lists.01.org, lkp@intel.com, zhengjun.xing@intel.com, aubrey.li@linux.intel.com, yu.c.chen@intel.com Subject: Re: [LKP] Re: [sched/hotplug] 2558aacff8: will-it-scale.per_thread_ops -1.6% regression Message-ID: <20201215083732.GC3040@hirez.programming.kicks-ass.net> References: <20201210081859.GA19784@xsang-OptiPlex-9020> <20201210161408.GX3021@hirez.programming.kicks-ass.net> <33c543f8-97c9-cb18-a2f8-a90b8a5769cc@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <33c543f8-97c9-cb18-a2f8-a90b8a5769cc@linux.intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 15, 2020 at 01:35:46PM +0800, Xing Zhengjun wrote: > On 12/11/2020 12:14 AM, Peter Zijlstra wrote: > > On Thu, Dec 10, 2020 at 04:18:59PM +0800, kernel test robot wrote: > > > FYI, we noticed a -1.6% regression of will-it-scale.per_thread_ops due to commit: > > > commit: 2558aacff8586699bcd248b406febb28b0a25de2 ("sched/hotplug: Ensure only per-cpu kthreads run during hotplug") > > > > Mooo, weird but whatever. Does the below help at all? > > I test the patch Thanks! > , the regression reduced to -0.6%. > > ========================================================================================= > tbox_group/testcase/rootfs/kconfig/compiler/nr_task/mode/test/cpufreq_governor/ucode: > > lkp-cpl-4sp1/will-it-scale/debian-10.4-x86_64-20200603.cgz/x86_64-rhel-8.3/gcc-9/100%/thread/sched_yield/performance/0x700001e > > commit: > 565790d28b1e33ee2f77bad5348b99f6dfc366fd > 2558aacff8586699bcd248b406febb28b0a25de2 > 4b26139b8db627a55043183614a32b0aba799d27 (this test patch) > > 565790d28b1e33ee 2558aacff8586699bcd248b406f 4b26139b8db627a55043183614a > ---------------- --------------------------- --------------------------- > %stddev %change %stddev %change %stddev > \ | \ | \ > 4.011e+08 -1.6% 3.945e+08 -0.6% 3.989e+08 will-it-scale.144.threads > 2785455 -1.6% 2739520 -0.6% 2769967 will-it-scale.per_thread_ops > 4.011e+08 -1.6% 3.945e+08 -0.6% 3.989e+08 will-it-scale.workload Well, that's better. But I'm rather confused now, because with this new patch, the actual hot paths are identical, so I've no idea what is actually causing the regression :/ The above numbers don't seem to have variance, how sure are we the results are stable? The thing is, when I tried reproducing this locally, I was mostly looking at noise. > > --- > > kernel/sched/core.c | 40 +++++++++++++++------------------------- > > kernel/sched/sched.h | 13 +++++-------- > > 2 files changed, 20 insertions(+), 33 deletions(-) Anyway, let me queue this in sched/urgent, it's simpler code and has less regression.