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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY, URIBL_BLOCKED,USER_AGENT_SANE_1 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 0077AC433B4 for ; Thu, 29 Apr 2021 03:28:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D4D6B6144F for ; Thu, 29 Apr 2021 03:28:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229888AbhD2D3C (ORCPT ); Wed, 28 Apr 2021 23:29:02 -0400 Received: from out4436.biz.mail.alibaba.com ([47.88.44.36]:23681 "EHLO out4436.biz.mail.alibaba.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229805AbhD2D3C (ORCPT ); Wed, 28 Apr 2021 23:29:02 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R191e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=alimailimapcm10staff010182156082;MF=haoxu@linux.alibaba.com;NM=1;PH=DS;RN=4;SR=0;TI=SMTPD_---0UX7Mp1E_1619666884; Received: from B-25KNML85-0107.local(mailfrom:haoxu@linux.alibaba.com fp:SMTPD_---0UX7Mp1E_1619666884) by smtp.aliyun-inc.com(127.0.0.1); Thu, 29 Apr 2021 11:28:05 +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> From: Hao Xu Message-ID: <51308ac4-03b7-0f66-7f26-8678807195ca@linux.alibaba.com> Date: Thu, 29 Apr 2021 11:28:04 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.9.1 MIME-Version: 1.0 In-Reply-To: <7136bf4f-089f-25d5-eaf8-1f55b946c005@gmail.com> 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 2021/4/28 下午10:07, Pavel Begunkov 写道: > On 4/28/21 2:32 PM, Hao Xu wrote: >> currently unit of io_sq_thread_idle is millisecond, the smallest value >> is 1ms, which means for IOPS > 1000, sqthread will very likely take >> 100% cpu usage. This is not necessary in some cases, like users may >> don't care about latency much in low IO pressure >> (like 1000 < IOPS < 20000), but cpu resource does matter. So we offer >> an option of nanosecond granularity of io_sq_thread_idle. Some test >> results by fio below: > > If numbers justify it, I don't see why not do it in ns, but I'd suggest > to get rid of all the mess and simply convert to jiffies during ring > creation (i.e. nsecs_to_jiffies64()), and leave io_sq_thread() unchanged. 1) here I keep millisecond mode for compatibility 2) I saw jiffies is calculated by HZ, and HZ could be large enough (like HZ = 1000) to make nsecs_to_jiffies64() = 0: u64 nsecs_to_jiffies64(u64 n) { #if (NSEC_PER_SEC % HZ) == 0 /* Common case, HZ = 100, 128, 200, 250, 256, 500, 512, 1000 etc. */ return div_u64(n, NSEC_PER_SEC / HZ); #elif (HZ % 512) == 0 /* overflow after 292 years if HZ = 1024 */ return div_u64(n * HZ / 512, NSEC_PER_SEC / 512); #else /* ¦* Generic case - optimized for cases where HZ is a multiple of 3. ¦* overflow after 64.99 years, exact for HZ = 60, 72, 90, 120 etc. ¦*/ return div_u64(n * 9, (9ull * NSEC_PER_SEC + HZ / 2) / HZ); #endif } say HZ = 1000, then nsec_to_jiffies64(1us) = 1e3 / (1e9 / 1e3) = 0 iow, nsec_to_jiffies64() doesn't work for n < (1e9 / HZ). > > Or is there a reason for having it high precision, i.e. ktime()? > >> uring average latency:(us) >> iops\idle 10us 60us 110us 160us 210us 260us 310us 360us 410us 460us 510us >> 2k 10.93 10.68 10.72 10.7 10.79 10.52 10.59 10.54 10.47 10.39 8.4 >> 4k 10.55 10.48 10.51 10.42 10.35 8.34 >> 6k 10.82 10.5 10.39 8.4 >> 8k 10.44 10.45 10.34 8.39 >> 10k 10.45 10.39 8.33 >> >> uring cpu usage of sqthread: >> iops\idle 10us 60us 110us 160us 210us 260us 310us 360us 410us 460us 510us >> 2k 4% 14% 24% 34.70% 44.70% 55% 65.10% 75.40% 85.40% 95.70% 100% >> 4k 7.70% 28.20% 48.50% 69% 90% 100% >> 6k 11.30% 42% 73% 100% >> 8k 15.30% 56.30% 97% 100% >> 10k 19% 70% 100% >> >> aio average latency:(us) >> iops latency 99th lat cpu >> 2k 13.34 14.272 3% >> 4k 13.195 14.016 7% >> 6k 13.29 14.656 9.70% >> 8k 13.2 14.656 12.70% >> 10k 13.2 15 17% >> >> fio config is: >> ./run_fio.sh >> fio \ >> --ioengine=io_uring --sqthread_poll=1 --hipri=1 --thread=1 --bs=4k \ >> --direct=1 --rw=randread --time_based=1 --runtime=300 \ >> --group_reporting=1 --filename=/dev/nvme1n1 --sqthread_poll_cpu=30 \ >> --randrepeat=0 --cpus_allowed=35 --iodepth=128 --rate_iops=${1} \ >> --io_sq_thread_idle=${2} >> >> in 2k IOPS, if latency of 10.93us is acceptable for an application, >> then they get 100% - 4% = 96% reduction of cpu usage, while the latency >> is smaller than aio(10.93us vs 13.34us). >> >> Signed-off-by: Hao Xu >> --- > [snip] >> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h >> index e1ae46683301..311532ff6ce3 100644 >> --- a/include/uapi/linux/io_uring.h >> +++ b/include/uapi/linux/io_uring.h >> @@ -98,6 +98,7 @@ enum { >> #define IORING_SETUP_CLAMP (1U << 4) /* clamp SQ/CQ ring sizes */ >> #define IORING_SETUP_ATTACH_WQ (1U << 5) /* attach to existing wq */ >> #define IORING_SETUP_R_DISABLED (1U << 6) /* start with ring disabled */ >> +#define IORING_SETUP_IDLE_NS (1U << 7) /* unit of thread_idle is nano second */ >> >> enum { >> IORING_OP_NOP, >> @@ -259,7 +260,7 @@ struct io_uring_params { >> __u32 cq_entries; >> __u32 flags; >> __u32 sq_thread_cpu; >> - __u32 sq_thread_idle; >> + __u64 sq_thread_idle; > > breaks userspace API > >> __u32 features; >> __u32 wq_fd; >> __u32 resv[3]; >> >