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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,UNPARSEABLE_RELAY 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 3FAD4C43381 for ; Fri, 8 Mar 2019 00:35:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1345F20854 for ; Fri, 8 Mar 2019 00:35:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726309AbfCHAfV (ORCPT ); Thu, 7 Mar 2019 19:35:21 -0500 Received: from out30-56.freemail.mail.aliyun.com ([115.124.30.56]:40681 "EHLO out30-56.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726241AbfCHAfU (ORCPT ); Thu, 7 Mar 2019 19:35:20 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R161e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01f04396;MF=shile.zhang@linux.alibaba.com;NM=1;PH=DS;RN=5;SR=0;TI=SMTPD_---0TMDiYUt_1552005317; Received: from ali-6c96cfdd1403.local(mailfrom:shile.zhang@linux.alibaba.com fp:SMTPD_---0TMDiYUt_1552005317) by smtp.aliyun-inc.com(127.0.0.1); Fri, 08 Mar 2019 08:35:17 +0800 Subject: Re: [PATCH] bcache: add cond_resched() in __bch_cache_cmp() To: Vojtech Pavlik , Coly Li Cc: Kent Overstreet , linux-bcache@vger.kernel.org, linux-kernel@vger.kernel.org References: <1551935728-243664-1-git-send-email-shile.zhang@linux.alibaba.com> <24916a71-39ff-7324-ad12-9d79cc68d0da@suse.de> <3640cd7f-f32a-1509-dbef-6000b6e14e75@linux.alibaba.com> <20190307154421.GA8829@suse.cz> From: Shile Zhang Message-ID: Date: Fri, 8 Mar 2019 08:35:17 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: <20190307154421.GA8829@suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019/3/7 23:44, Vojtech Pavlik wrote: > On Thu, Mar 07, 2019 at 11:36:18PM +0800, Coly Li wrote: >> On 2019/3/7 11:06 下午, Shile Zhang wrote: >>> On 2019/3/7 18:34, Coly Li wrote: >>>> On 2019/3/7 1:15 下午, shile.zhang@linux.alibaba.com wrote: >>>>> From: Shile Zhang >>>>> >>>>> Read /sys/fs/bcache//cacheN/priority_stats can take very long >>>>> time with huge cache after long run. >>>>> >>>>> Signed-off-by: Shile Zhang >>>> Hi Shile, >>>> >>>> Do you test your change ? It will be helpful with more performance data >>>> (what problem that you improved). >>> In case of 960GB SSD cache device, once read of the 'priority_stats' >>> costs about 600ms in our test environment. >>> >> After the fix, how much time it takes ? >> >> >>> The perf tool shown that near 50% CPU time consumed by 'sort()', this >>> means once sort will hold the CPU near 300ms. >>> >>> In our case, the statistics collector reads the 'priority_stats' >>> periodically, it will trigger the schedule latency jitters of the >>> >>> task which shared same CPU core. >>> >> Hmm, it seems you just make the sort slower, and nothing more changes. >> Am I right ? > Well, it has to make the sort slower, but it'll also avoid hogging the > CPU (on a non-preemptible kernel), avoiding a potential soft lockup > warning and allowing other tasks to run. > Yes, there is a risk that other tasks have no chance to run due to sort hogging the CPU, it is harmful to some schedule-latency sensitive tasks. This change just try to reduce the impact of sort, but not a performance improvement of it. I'm not sure if a better way can handle it more efficiency. Thanks, Shile