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 D6C70C433E7 for ; Wed, 14 Oct 2020 10:19:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 90EA620723 for ; Wed, 14 Oct 2020 10:19:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729403AbgJNKTG (ORCPT ); Wed, 14 Oct 2020 06:19:06 -0400 Received: from mx2.suse.de ([195.135.220.15]:50732 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726439AbgJNKTG (ORCPT ); Wed, 14 Oct 2020 06:19:06 -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 EC59BABA2; Wed, 14 Oct 2020 10:19:04 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 643371E1338; Wed, 14 Oct 2020 12:19:04 +0200 (CEST) Date: Wed, 14 Oct 2020 12:19:04 +0200 From: Jan Kara To: kernel test robot Cc: NeilBrown , Linus Torvalds , Andrew Morton , Jan Kara , 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 Subject: Re: [mm/writeback] 8d92890bd6: will-it-scale.per_process_ops -15.3% regression Message-ID: <20201014101904.GA11144@quack2.suse.cz> References: <20201014084706.GB11647@shao2-debian> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201014084706.GB11647@shao2-debian> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Honza -- Jan Kara SUSE Labs, CR