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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,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 E5544CA9ECF for ; Fri, 1 Nov 2019 11:52:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C52BD21D71 for ; Fri, 1 Nov 2019 11:52:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730466AbfKALwV (ORCPT ); Fri, 1 Nov 2019 07:52:21 -0400 Received: from out30-133.freemail.mail.aliyun.com ([115.124.30.133]:35819 "EHLO out30-133.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726957AbfKALwV (ORCPT ); Fri, 1 Nov 2019 07:52:21 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R151e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04426;MF=yun.wang@linux.alibaba.com;NM=1;PH=DS;RN=9;SR=0;TI=SMTPD_---0TgtH3hA_1572609135; Received: from testdeMacBook-Pro.local(mailfrom:yun.wang@linux.alibaba.com fp:SMTPD_---0TgtH3hA_1572609135) by smtp.aliyun-inc.com(127.0.0.1); Fri, 01 Nov 2019 19:52:16 +0800 Subject: Re: [PATCH] sched/numa: advanced per-cgroup numa statistic To: Mel Gorman Cc: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , linux-kernel@vger.kernel.org References: <46b0fd25-7b73-aa80-372a-9fcd025154cb@linux.alibaba.com> <20191030095505.GF28938@suse.de> <6f5e43db-24f1-5283-0881-f264b0d5f835@linux.alibaba.com> <20191031131731.GJ28938@suse.de> <5d69ff1b-a477-31b5-8600-9233a38445c7@linux.alibaba.com> <20191101091348.GM28938@suse.de> From: =?UTF-8?B?546L6LSH?= Message-ID: <2573b108-7885-5c4f-a0ae-2b245d663250@linux.alibaba.com> Date: Fri, 1 Nov 2019 19:52:15 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20191101091348.GM28938@suse.de> Content-Type: text/plain; charset=UTF-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019/11/1 下午5:13, Mel Gorman wrote: [snip] >> For example in our cases, we could have hundreds of cgroups, each contain >> hundreds of tasks, these worker thread could live and die at any moment, >> for gathering we need to cat the list of tasks and then go reading these proc >> files one by one, which fall into kernel rapidly and may even need to holding >> some locks, this introduced big latency impact, and give no accurate output >> since some task may already died before reading it's data. >> >> Then before next sample window, info of tasks died during the window can't be >> acquired anymore. >> >> We need kernel's help on reserving data since tool can't catch them in time >> before they are lost, also we have to avoid rapidly proc reading, which really >> cost a lot and further more, introduce big latency on each sample window. >> > > There is somewhat of a disconnect here. You say that the information must > be accurate and historical yet are relying on NUMA hinting faults to build > the picture which may not be accurate at all given that faults are not > guaranteed to happen. For short-lived tasks, it is also potentially skewed > information if short-lived tasks dominated remote accesses for whatever > reason even though it does not matter -- the tasks were short-lived and > their performance is probably irrelevant. Short-lived tasks may not even > show up if they do not run longer than sysctl_numa_balancing_scan_delay > so the data gathered already has holes in it. > > While it's a bit more of a stretch, even this could still be done from > userspace if numa_hint_fault was probed and the event handled (eBPF, > systemtap etc) to build the picture or add a tracepoint. That would give > a much higher degree of flexibility on what information is tracked and > allow flexibility on > > So, overall I think this can be done outside the kernel but recognise > that it may not be suitable in all cases. If you feel it must be done > inside the kernel, split out the patch that adds information on failed > page migrations as it stands apart. Put it behind its own kconfig entry > that is disabled by default -- do not tie it directly to NUMA balancing > because of the data structure changes. When enabled, it should still be > disabled by default at runtime and only activated via kernel command line > parameter so that the only people who pay the cost are those that take > deliberate action to enable it. Agree, we could have these per-task faults info there, give the possibility to implement maybe a practical userland tool, meanwhile have these kernel numa data disabled by default, folks who got no tool but want to do easy monitoring can just turn on the switch :-) Will have these in next version: * separate patch for showing per-task faults info * new CONFIG for numa stat (disabled by default) * dynamical runtime switch for numa stat (disabled by default) * doc to explain the numa stat and give hint on how to handle it Best Regards, Michale Wang >