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=-7.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS, UNPARSEABLE_RELAY,USER_AGENT_SANE_1 autolearn=unavailable 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 648FFC2D0DC for ; Thu, 26 Dec 2019 16:42:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3C3A020828 for ; Thu, 26 Dec 2019 16:42:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726994AbfLZQmX (ORCPT ); Thu, 26 Dec 2019 11:42:23 -0500 Received: from out30-130.freemail.mail.aliyun.com ([115.124.30.130]:46757 "EHLO out30-130.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726597AbfLZQmX (ORCPT ); Thu, 26 Dec 2019 11:42:23 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R261e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e01422;MF=wenyang@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0Tm-.zlD_1577378536; Received: from IT-C02W23QPG8WN.local(mailfrom:wenyang@linux.alibaba.com fp:SMTPD_---0Tm-.zlD_1577378536) by smtp.aliyun-inc.com(127.0.0.1); Fri, 27 Dec 2019 00:42:17 +0800 Subject: Re: [PATCH v2] block: make the io_ticks counter more accurate To: Jens Axboe Cc: Joseph Qi , xlpang@linux.alibaba.com, Mikulas Patocka , Mike Snitzer , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org References: <20191226031014.58970-1-wenyang@linux.alibaba.com> <41175786-8a02-62e0-fc79-955ec0e74aeb@kernel.dk> From: Wen Yang Message-ID: <533328c7-4158-d9fd-d8db-0d02eb9c5108@linux.alibaba.com> Date: Fri, 27 Dec 2019 00:42:16 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <41175786-8a02-62e0-fc79-955ec0e74aeb@kernel.dk> Content-Type: text/plain; charset=utf-8; format=flowed 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 2019/12/26 11:39 上午, Jens Axboe wrote: > On 12/25/19 8:10 PM, Wen Yang wrote: >> Instead of the jiffies, we should update the io_ticks counter >> with the passed in parameter 'now'. > > I'm still missing some justification for this. What exactly is this > patch trying to solve or improve? Your commit message says "we should", > but why? > Hi Jens, Thank you for your comments. We observed in the document that: io_ticks ======== This value counts the number of milliseconds during which the device has had I/O requests queued. And the iostat command uses io_ticks count to calculate %util: https://github.com/sysstat/sysstat/blob/master/rd_stats.c#L372 eg： Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await r_await w_await svctm %util So we need to unify the time windows of these statistics（io_ticks, rd_tick, time_in_queue, etc）. However, the current code uses jiffies to count io_ticks. Jiffies is different from the passed in parameter 'now', so these statistics will be inconsistent： void blk_account_io_done(struct request *req, u64 now) { … update_io_ticks(part, jiffies); part_stat_inc(part, ios[sgrp]); part_stat_add(part, nsecs[sgrp], now - req->start_time_ns); part_stat_add(part, time_in_queue, nsecs_to_jiffies64(now - req->start_time_ns)); … } In addition, we also found another issue: the update_io_tick() function only adds one to io_ticks at a time, which will result in the calculated %util lower than the real one. https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/block/bio.c#n1713 We will try our best to improve it. please kindly help with some suggestions. Thanks. -- Best Regards, Wen