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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,UNPARSEABLE_RELAY,USER_AGENT_SANE_1 autolearn=no 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 7C46CC2D0A3 for ; Tue, 10 Nov 2020 03:06:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0DB7E2067B for ; Tue, 10 Nov 2020 03:06:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729451AbgKJDGE (ORCPT ); Mon, 9 Nov 2020 22:06:04 -0500 Received: from out30-42.freemail.mail.aliyun.com ([115.124.30.42]:50452 "EHLO out30-42.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728607AbgKJDGE (ORCPT ); Mon, 9 Nov 2020 22:06:04 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R171e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04394;MF=xiaoguang.wang@linux.alibaba.com;NM=1;PH=DS;RN=3;SR=0;TI=SMTPD_---0UEpi9pn_1604977561; Received: from 30.225.32.17(mailfrom:xiaoguang.wang@linux.alibaba.com fp:SMTPD_---0UEpi9pn_1604977561) by smtp.aliyun-inc.com(127.0.0.1); Tue, 10 Nov 2020 11:06:01 +0800 Subject: Re: [PATCH] io_uring: don't take percpu_ref operations for registered files in IOPOLL mode To: Jens Axboe , io-uring@vger.kernel.org Cc: joseph.qi@linux.alibaba.com References: <20200902050538.8350-1-xiaoguang.wang@linux.alibaba.com> <2eb73693-9c40-d657-b822-548ddd92b875@linux.alibaba.com> <764234cf-ab08-7ccf-f4b6-b0a2f5ae6cbc@kernel.dk> From: Xiaoguang Wang Message-ID: Date: Tue, 10 Nov 2020 11:04:48 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.4.1 MIME-Version: 1.0 In-Reply-To: <764234cf-ab08-7ccf-f4b6-b0a2f5ae6cbc@kernel.dk> Content-Type: text/plain; charset=gbk; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org hi, > On 11/4/20 8:20 PM, Xiaoguang Wang wrote: >> hi, >> >>> In io_file_get() and io_put_file(), currently we use percpu_ref_get() and >>> percpu_ref_put() for registered files, but it's hard to say they're very >>> light-weight synchronization primitives, especially in arm platform. In one >>> our arm machine, I get below perf data(registered files enabled): >>> Samples: 98K of event 'cycles:ppp', Event count (approx.): 63789396810 >>> Overhead Command Shared Object Symbol >>> ... >>> 0.78% io_uring-sq [kernel.vmlinux] [k] io_file_get >>> There is an obvious overhead that can not be ignored. >>> >>> Currently I don't find any good and generic solution for this issue, but >>> in IOPOLL mode, given that we can always ensure get/put registered files >>> under uring_lock, we can use a simple and plain u64 counter to synchronize >>> with registered files update operations in __io_sqe_files_update(). >>> >>> With this patch, perf data show shows: >>> Samples: 104K of event 'cycles:ppp', Event count (approx.): 67478249890 >>> Overhead Command Shared Object Symbol >>> ... >>> 0.27% io_uring-sq [kernel.vmlinux] [k] io_file_get >> The above %0.78 => %0.27 improvements are observed in arm machine with >> 4.19 kernel. In upstream mainline codes, since this patch >> "2b0d3d3e4fcf percpu_ref: reduce memory footprint of percpu_ref in >> fast path", I believe the io_file_get's overhead would be further >> smaller. I have same tests in same machine, in upstream codes with my >> patch, now the io_file_get's overhead is %0.44. >> >> This patch's idea is simple, and now seems it only gives minor >> performance improvement, do you have any comments about this patch, >> should I continue re-send it? > > Can you resend it against for-5.11/io_uring? Looks simple enough to me, > and it's a nice little win.Thanks, I'll prepare V2 soon. Regards, Xiaoguang Wang >