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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 6228AC433DB for ; Mon, 4 Jan 2021 14:12:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2BFEB207BC for ; Mon, 4 Jan 2021 14:12:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727213AbhADOM2 (ORCPT ); Mon, 4 Jan 2021 09:12:28 -0500 Received: from mx2.suse.de ([195.135.220.15]:52254 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726189AbhADOM2 (ORCPT ); Mon, 4 Jan 2021 09:12:28 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1609769501; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=PpHTWcsYu9aNWGoDskPr9Uf5ufkrRwaG/jWt3MgTzyA=; b=rq1Z8r68W7HjqKG1WwTpf79rB+ObjSTRRi/+lAubzIldoZmbbcVXbwNYyzlX2VKD5BvgrY Vu8U1EoQwJG5Fe1as9KIiwZyf7IZrX95roWS1rUMbaiVY6pTDLi7+8mfxrWsabeGEtg/R1 fFX8iN1OEhm1uzFOMTF/a9zQCmwP7hY= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 403AFB770; Mon, 4 Jan 2021 14:11:41 +0000 (UTC) Date: Mon, 4 Jan 2021 15:11:40 +0100 From: Michal Hocko To: Feng Tang Cc: Andrew Morton , Johannes Weiner , Vladimir Davydov , linux-mm@kvack.org, linux-kernel@vger.kernel.org, andi.kleen@intel.com, tim.c.chen@intel.com, dave.hansen@intel.com, ying.huang@intel.com, Roman Gushchin Subject: Re: [PATCH 1/2] mm: page_counter: relayout structure to reduce false sharing Message-ID: <20210104141140.GH13207@dhcp22.suse.cz> References: <1609252514-27795-1-git-send-email-feng.tang@intel.com> <20210104130357.GF13207@dhcp22.suse.cz> <20210104133445.GA101866@shbuild999.sh.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210104133445.GA101866@shbuild999.sh.intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 04-01-21 21:34:45, Feng Tang wrote: > Hi Michal, > > On Mon, Jan 04, 2021 at 02:03:57PM +0100, Michal Hocko wrote: > > On Tue 29-12-20 22:35:13, Feng Tang wrote: > > > When checking a memory cgroup related performance regression [1], > > > from the perf c2c profiling data, we found high false sharing for > > > accessing 'usage' and 'parent'. > > > > > > On 64 bit system, the 'usage' and 'parent' are close to each other, > > > and easy to be in one cacheline (for cacheline size == 64+ B). 'usage' > > > is usally written, while 'parent' is usually read as the cgroup's > > > hierarchical counting nature. > > > > > > So move the 'parent' to the end of the structure to make sure they > > > are in different cache lines. > > > > Yes, parent is write-once field so having it away from other heavy RW > > fields makes sense to me. > > > > > Following are some performance data with the patch, against > > > v5.11-rc1, on several generations of Xeon platforms. Most of the > > > results are improvements, with only one malloc case on one platform > > > shows a -4.0% regression. Each category below has several subcases > > > run on different platform, and only the worst and best scores are > > > listed: > > > > > > fio: +1.8% ~ +8.3% > > > will-it-scale/malloc1: -4.0% ~ +8.9% > > > will-it-scale/page_fault1: no change > > > will-it-scale/page_fault2: +2.4% ~ +20.2% > > > > What is the second number? Std? > > For each case like 'page_fault2', I run several subcases on different > generations of Xeon, and only listed the lowest (first number) and > highest (second number) scores. > > There are 5 runs and the result are: +3.6%, +2.4%, +10.4%, +20.2%, > +4.7%, and +2.4% and +20.2% are listed. This should be really explained in the changelog and ideally mention the model as well. Seeing a std would be appreciated as well. -- Michal Hocko SUSE Labs