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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id EA93AC63705 for ; Wed, 7 Dec 2022 13:09:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229736AbiLGNJS (ORCPT ); Wed, 7 Dec 2022 08:09:18 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44964 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229515AbiLGNJR (ORCPT ); Wed, 7 Dec 2022 08:09:17 -0500 Received: from dggsgout11.his.huawei.com (unknown [45.249.212.51]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EADED554E8; Wed, 7 Dec 2022 05:09:15 -0800 (PST) Received: from mail02.huawei.com (unknown [172.30.67.153]) by dggsgout11.his.huawei.com (SkyGuard) with ESMTP id 4NRyKc2Vfmz4f3w0Q; Wed, 7 Dec 2022 21:09:08 +0800 (CST) Received: from [10.174.176.73] (unknown [10.174.176.73]) by APP4 (Coremail) with SMTP id gCh0CgBni9h0kJBjx41CBw--.7669S3; Wed, 07 Dec 2022 21:09:11 +0800 (CST) Subject: Re: [RFC] block: Change the granularity of io ticks from ms to ns To: Ming Lei , Yu Kuai Cc: Gulam Mohamed , linux-block@vger.kernel.org, axboe@kernel.dk, philipp.reisner@linbit.com, lars.ellenberg@linbit.com, christoph.boehmwalder@linbit.com, minchan@kernel.org, ngupta@vflare.org, senozhatsky@chromium.org, colyli@suse.de, kent.overstreet@gmail.com, agk@redhat.com, snitzer@kernel.org, dm-devel@redhat.com, song@kernel.org, dan.j.williams@intel.com, vishal.l.verma@intel.com, dave.jiang@intel.com, ira.weiny@intel.com, junxiao.bi@oracle.com, martin.petersen@oracle.com, kch@nvidia.com, drbd-dev@lists.linbit.com, linux-kernel@vger.kernel.org, linux-bcache@vger.kernel.org, linux-raid@vger.kernel.org, nvdimm@lists.linux.dev, konrad.wilk@oracle.com, "yukuai (C)" References: <20221206181536.13333-1-gulam.mohamed@oracle.com> <936a498b-19fe-36d5-ff32-817f153e57e3@huaweicloud.com> From: Yu Kuai Message-ID: Date: Wed, 7 Dec 2022 21:09:08 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit X-CM-TRANSID: gCh0CgBni9h0kJBjx41CBw--.7669S3 X-Coremail-Antispam: 1UD129KBjvJXoWrKF13ZrWDCw43Cw15CF1DAwb_yoW8Jr4kpr y3A3ZIkw48WFyFkwnFya1UJrWYvrn3ArZ8uFW5K3s7trn0kas3Jr4UG3WDCF92gFsIkF12 gay2gas8ur48C3DanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUU9F14x267AKxVWrJVCq3wAFc2x0x2IEx4CE42xK8VAvwI8IcIk0 rVWrJVCq3wAFIxvE14AKwVWUJVWUGwA2ocxC64kIII0Yj41l84x0c7CEw4AK67xGY2AK02 1l84ACjcxK6xIIjxv20xvE14v26w1j6s0DM28EF7xvwVC0I7IYx2IY6xkF7I0E14v26r4U JVWxJr1l84ACjcxK6I8E87Iv67AKxVW0oVCq3wA2z4x0Y4vEx4A2jsIEc7CjxVAFwI0_Gc CE3s1le2I262IYc4CY6c8Ij28IcVAaY2xG8wAqx4xG64xvF2IEw4CE5I8CrVC2j2WlYx0E 2Ix0cI8IcVAFwI0_Jr0_Jr4lYx0Ex4A2jsIE14v26r1j6r4UMcvjeVCFs4IE7xkEbVWUJV W8JwACjcxG0xvEwIxGrwACjI8F5VA0II8E6IAqYI8I648v4I1lFIxGxcIEc7CjxVA2Y2ka 0xkIwI1lc7I2V7IY0VAS07AlzVAYIcxG8wCF04k20xvY0x0EwIxGrwCFx2IqxVCFs4IE7x kEbVWUJVW8JwC20s026c02F40E14v26r1j6r18MI8I3I0E7480Y4vE14v26r106r1rMI8E 67AF67kF1VAFwI0_GFv_WrylIxkGc2Ij64vIr41lIxAIcVC0I7IYx2IY67AKxVWUJVWUCw CI42IY6xIIjxv20xvEc7CjxVAFwI0_Gr0_Cr1lIxAIcVCF04k26cxKx2IYs7xG6rW3Jr0E 3s1lIxAIcVC2z280aVAFwI0_Jr0_Gr1lIxAIcVC2z280aVCY1x0267AKxVW8JVW8JrUvcS sGvfC2KfnxnUUI43ZEXa7VUbJ73DUUUUU== X-CM-SenderInfo: 51xn3trlr6x35dzhxuhorxvhhfrp/ X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Hi, 在 2022/12/07 11:15, Ming Lei 写道: > On Wed, Dec 07, 2022 at 10:19:08AM +0800, Yu Kuai wrote: >> Hi, >> >> 在 2022/12/07 2:15, Gulam Mohamed 写道: >>> Use ktime to change the granularity of IO accounting in block layer from >>> milli-seconds to nano-seconds to get the proper latency values for the >>> devices whose latency is in micro-seconds. After changing the granularity >>> to nano-seconds the iostat command, which was showing incorrect values for >>> %util, is now showing correct values. >> >> This patch didn't correct the counting of io_ticks, just make the >> error accounting from jiffies(ms) to ns. The problem that util can be >> smaller or larger still exist. > > Agree. > >> >> However, I think this change make sense consider that error margin is >> much smaller, and performance overhead should be minimum. >> >> Hi, Ming, how do you think? > > I remembered that ktime_get() has non-negligible overhead, is there any > test data(iops/cpu utilization) when running fio or t/io_uring on > null_blk with this patch? Yes, testing with null_blk is necessary, we don't want any performance regression. BTW, I thought it's fine because it's already used for tracking io latency. > > > Thanks, > Ming > > > . >