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=-10.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,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 B1718C433E7 for ; Fri, 16 Oct 2020 14:51:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7510A21527 for ; Fri, 16 Oct 2020 14:51:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2409216AbgJPOvi (ORCPT ); Fri, 16 Oct 2020 10:51:38 -0400 Received: from mga12.intel.com ([192.55.52.136]:28909 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2409071AbgJPOvf (ORCPT ); Fri, 16 Oct 2020 10:51:35 -0400 IronPort-SDR: 2daS5uibJmiAUNHDk1JuG8ZkHLZ+JXyRWr6+B2bjUQixlAQ35fNfphL+DiO5k3DyKBwawlwTQp YItzByGcVb3A== X-IronPort-AV: E=McAfee;i="6000,8403,9775"; a="145931156" X-IronPort-AV: E=Sophos;i="5.77,383,1596524400"; d="scan'208";a="145931156" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga004.jf.intel.com ([10.7.209.38]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 16 Oct 2020 07:51:34 -0700 IronPort-SDR: W2gGSueEDce8Ckr4AlvPLkcTKsRAk8PchgmOKN5iW9AbLevJM5B/X9cShyyuB1ykN4sMC3536H ztgaihoVXfcg== X-IronPort-AV: E=Sophos;i="5.77,383,1596524400"; d="scan'208";a="464702829" Received: from rongch2-mobl.ccr.corp.intel.com (HELO [10.249.172.186]) ([10.249.172.186]) by orsmga004-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 16 Oct 2020 07:51:29 -0700 Subject: Re: [mm/writeback] 8d92890bd6: will-it-scale.per_process_ops -15.3% regression To: Jan Kara , NeilBrown Cc: Linus Torvalds , Andrew Morton , Christoph Hellwig , Trond Myklebust , Chuck Lever , LKML , lkp@lists.01.org, lkp@intel.com, ying.huang@intel.com, feng.tang@intel.com, zhengjun.xing@intel.com References: <20201014084706.GB11647@shao2-debian> <20201014101904.GA11144@quack2.suse.cz> <87pn5kfply.fsf@notabene.neil.brown.name> <20201015090843.GA7037@quack2.suse.cz> <20201015091254.GB7037@quack2.suse.cz> From: "Chen, Rong A" Message-ID: <08f0ec04-ab69-84ab-eadb-89f67c453b6b@intel.com> Date: Fri, 16 Oct 2020 22:51:25 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <20201015091254.GB7037@quack2.suse.cz> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/15/2020 5:12 PM, Jan Kara wrote: > On Thu 15-10-20 11:08:43, Jan Kara wrote: >> On Thu 15-10-20 08:46:01, NeilBrown wrote: >>> On Wed, Oct 14 2020, Jan Kara wrote: >>> >>>> On Wed 14-10-20 16:47:06, kernel test robot wrote: >>>>> Greeting, >>>>> >>>>> FYI, we noticed a -15.3% regression of will-it-scale.per_process_ops due >>>>> to commit: >>>>> >>>>> commit: 8d92890bd6b8502d6aee4b37430ae6444ade7a8c ("mm/writeback: discard >>>>> NR_UNSTABLE_NFS, use NR_WRITEBACK instead") >>>>> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master >>>> >>>> Thanks for report but it doesn't quite make sense to me. If we omit >>>> reporting & NFS changes in that commit (which is code not excercised by >>>> this benchmark), what remains are changes like: >>>> >>>> nr_pages += node_page_state(pgdat, NR_FILE_DIRTY); >>>> - nr_pages += node_page_state(pgdat, NR_UNSTABLE_NFS); >>>> nr_pages += node_page_state(pgdat, NR_WRITEBACK); >>>> ... >>>> - nr_reclaimable = global_node_page_state(NR_FILE_DIRTY) + >>>> - global_node_page_state(NR_UNSTABLE_NFS); >>>> + nr_reclaimable = global_node_page_state(NR_FILE_DIRTY); >>>> ... >>>> - gdtc->dirty = global_node_page_state(NR_FILE_DIRTY) + >>>> - global_node_page_state(NR_UNSTABLE_NFS); >>>> + gdtc->dirty = global_node_page_state(NR_FILE_DIRTY); >>>> >>>> So if there's any negative performance impact of these changes, they're >>>> likely due to code alignment changes or something like that... So I don't >>>> think there's much to do here since optimal code alignment is highly specific >>>> to a particular CPU etc. >>> >>> I agree, it seems odd. >>> >>> Removing NR_UNSTABLE_NFS from enum node_stat_item would renumber all the >>> following value and would, I think, change NR_DIRTIED from 32 to 31. >>> Might that move something to a different cache line and change some >>> contention? >> >> Interesting theory, it could be possible. >> >>> That would be easy enough to test: just re-add NR_UNSTABLE_NFS. >> >> Yeah, easy enough to test. Patch for this is attached. 0-day people, can >> you check whether applying this patch changes anything in your perf >> numbers? > > Forgot the patch. Attached now. > > Honza > Hi, We tested the patch and the regression became worse, but as you said the problem seems odd, so we tested v5.9 and regression already disappeared. a37b0715ddf30077 8d92890bd6b8502d6aee4b37430 v5.9 ---------------- --------------------------- --------------------------- %stddev %change %stddev %change %stddev \ | \ | \ 341015 ± 9% -18.4% 278292 +32.4% 451473 will-it-scale.per_process_ops 65475001 ± 9% -18.4% 53432256 +32.4% 86682938 will-it-scale.workload Best Regards, Rong Chen