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=-6.1 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 6411EC433EF for ; Fri, 3 Sep 2021 07:22:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 45568610A2 for ; Fri, 3 Sep 2021 07:22:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1347750AbhICHX5 (ORCPT ); Fri, 3 Sep 2021 03:23:57 -0400 Received: from mga03.intel.com ([134.134.136.65]:45465 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234791AbhICHX4 (ORCPT ); Fri, 3 Sep 2021 03:23:56 -0400 X-IronPort-AV: E=McAfee;i="6200,9189,10095"; a="219412694" X-IronPort-AV: E=Sophos;i="5.85,264,1624345200"; d="scan'208";a="219412694" Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Sep 2021 00:22:47 -0700 X-IronPort-AV: E=Sophos;i="5.85,264,1624345200"; d="scan'208";a="533766730" Received: from xingzhen-mobl.ccr.corp.intel.com (HELO [10.238.4.90]) ([10.238.4.90]) by fmsmga003-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Sep 2021 00:22:45 -0700 Subject: Re: [LKP] Re: [sched/fair] c722f35b51: tbench.throughput-MB/sec -29.1% regression To: Rik van Riel , kernel test robot Cc: Peter Zijlstra , Mel Gorman , LKML , lkp@lists.01.org, lkp@intel.com, aubrey.li@linux.intel.com, yu.c.chen@intel.com References: <20210519082211.GF29704@xsang-OptiPlex-9020> <1d942826-badc-ca0d-6d46-1b207caf7f84@intel.com> From: "Xing, Zhengjun" Message-ID: <304055ef-0c04-676b-3ed2-2b0cd0fe6d0b@intel.com> Date: Fri, 3 Sep 2021 15:22:43 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Rik,     Do you have time to look at this? I re-test it in v5.13 and v5.14, the regression still existed. Thanks. On 5/27/2021 10:00 AM, Rik van Riel wrote: > Hello, > > I will try to take a look at this on Friday. > > However, even if I manage to reproduce it on one of > the systems I have access to, I'm still not sure how > exactly we would root cause the issue. > > Is it due to > select_idle_sibling() doing a little bit > more work? > > Is it because we invoke test_idle_cores() a little > earlier, widening the race window with CPUs going idle, > causing select_idle_cpu to do a lot more work? > > Is it a locality thing where random placement on any > core in the LLC is somehow better than placement on > the same core as "prev" when there is no idle core? > > Is it tbench running > faster when the woken up task is > placed on the runqueue behind the current task on the > "target" cpu, even though that CPU isn't currently > idle, because tbench happens to go to sleep fast? > > In other words, I'm > not quite sure whether this is > a tbench (and other similar benchmark) specific thing, > or a kernel thing, or what instrumentation we would > want in select_idle_sibling / select_idle_cpu for us > to root cause issues like this more easily in the > future... -- Zhengjun Xing