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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7D70BC433F5 for ; Wed, 29 Sep 2021 12:13:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 62B346138E for ; Wed, 29 Sep 2021 12:13:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343709AbhI2MO4 (ORCPT ); Wed, 29 Sep 2021 08:14:56 -0400 Received: from out30-45.freemail.mail.aliyun.com ([115.124.30.45]:38813 "EHLO out30-45.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1343700AbhI2MOw (ORCPT ); Wed, 29 Sep 2021 08:14:52 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R151e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04426;MF=haoxu@linux.alibaba.com;NM=1;PH=DS;RN=4;SR=0;TI=SMTPD_---0Uq1.5JF_1632917589; Received: from B-25KNML85-0107.local(mailfrom:haoxu@linux.alibaba.com fp:SMTPD_---0Uq1.5JF_1632917589) by smtp.aliyun-inc.com(127.0.0.1); Wed, 29 Sep 2021 20:13:09 +0800 Subject: Re: [PATCH RFC 5.13 1/2] io_uring: add support for ns granularity of io_sq_thread_idle To: Pavel Begunkov , Jens Axboe Cc: io-uring@vger.kernel.org, Joseph Qi References: <1619616748-17149-1-git-send-email-haoxu@linux.alibaba.com> <1619616748-17149-2-git-send-email-haoxu@linux.alibaba.com> <7136bf4f-089f-25d5-eaf8-1f55b946c005@gmail.com> <51308ac4-03b7-0f66-7f26-8678807195ca@linux.alibaba.com> <96ef70e8-7abf-d820-3cca-0f8aedc969d8@gmail.com> <0d781b5f-3d2d-5ad4-9ad3-8fabc994313a@linux.alibaba.com> <11c738b2-8024-1870-d54b-79e89c5bea54@gmail.com> <10358b7e-9eb3-290f-34b6-5f257e98bcb9@linux.alibaba.com> From: Hao Xu Message-ID: <5af509fe-b9f7-7913-defd-4d32d4f98f4e@linux.alibaba.com> Date: Wed, 29 Sep 2021 20:13:09 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; 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 Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org 在 2021/9/29 下午7:37, Pavel Begunkov 写道: > On 9/29/21 10:24 AM, Hao Xu wrote: >> 在 2021/9/28 下午6:51, Pavel Begunkov 写道: >>> On 9/26/21 11:00 AM, Hao Xu wrote: > [...] >>>> I'm gonna pick this one up again, currently this patch >>>> with ktime_get_ns() works good on our productions. This >>>> patch makes the latency a bit higher than before, but >>>> still lower than aio. >>>> I haven't gotten a faster alternate for ktime_get_ns(), >>>> any hints? >>> >>> Good, I'd suggest to look through Documentation/core-api/timekeeping.rst >>> In particular coarse variants may be of interest. >>> https://www.kernel.org/doc/html/latest/core-api/timekeeping.html#coarse-and-fast-ns-access >>> >> The coarse functions seems to be like jiffies, because they use the last >> timer tick(from the explanation in that doc, it seems the timer tick is >> in the same frequency as jiffies update). So I believe it is just >> another format of jiffies which is low accurate. > > I haven't looked into the details, but it seems that unlike jiffies for > the coarse mode 10ms (or whatever) is the worst case, but it _may_ be Maybe I'm wrong, but for jiffies, 10ms uis also the worst case, no? (say HZ = 100, then jiffies updated by 1 every 10ms) > much better on average and feasible for your case, but can't predict > if that's really the case in a real system and what will be the > relative error comparing to normal ktime_ns(). >