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 004F4C433EF for ; Wed, 2 Mar 2022 06:35:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239693AbiCBGgV (ORCPT ); Wed, 2 Mar 2022 01:36:21 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42872 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231644AbiCBGgV (ORCPT ); Wed, 2 Mar 2022 01:36:21 -0500 Received: from out199-10.us.a.mail.aliyun.com (out199-10.us.a.mail.aliyun.com [47.90.199.10]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 560645F8C4; Tue, 1 Mar 2022 22:35:38 -0800 (PST) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R991e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04423;MF=haoxu@linux.alibaba.com;NM=1;PH=DS;RN=5;SR=0;TI=SMTPD_---0V61Jf3z_1646202933; Received: from 30.226.12.26(mailfrom:haoxu@linux.alibaba.com fp:SMTPD_---0V61Jf3z_1646202933) by smtp.aliyun-inc.com(127.0.0.1); Wed, 02 Mar 2022 14:35:34 +0800 Message-ID: <970e752b-aa75-8f66-ae7a-65ab509bea10@linux.alibaba.com> Date: Wed, 2 Mar 2022 14:35:33 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Subject: Re: [PATCH v4 2/2] io_uring: Add support for napi_busy_poll Content-Language: en-US To: Olivier Langlois , Jens Axboe , Pavel Begunkov Cc: io-uring , linux-kernel References: <29bad95d-06f8-ea7c-29fe-81e52823c90a@linux.alibaba.com> From: Hao Xu 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 On 3/2/22 13:12, Olivier Langlois wrote: > On Wed, 2022-03-02 at 02:31 +0800, Hao Xu wrote: >>> +static void io_blocking_napi_busy_loop(struct list_head >>> *napi_list, >>> +                                      struct io_wait_queue *iowq) >>> +{ >>> +       unsigned long start_time = >>> +               list_is_singular(napi_list) ? 0 : >>> +               busy_loop_current_time(); >>> + >>> +       do { >>> +               if (list_is_singular(napi_list)) { >>> +                       struct napi_entry *ne = >>> +                               list_first_entry(napi_list, >>> +                                                struct napi_entry, >>> list); >>> + >>> +                       napi_busy_loop(ne->napi_id, >>> io_busy_loop_end, iowq, >>> +                                      true, BUSY_POLL_BUDGET); >>> +                       io_check_napi_entry_timeout(ne); >>> +                       break; >>> +               } >>> +       } while (io_napi_busy_loop(napi_list) && >>> +                !io_busy_loop_end(iowq, start_time)); >>> +} >>> + >> How about: >> >> if (list is singular) { >> >>      do something; >> >>      return; >> >> } >> >> while (!io_busy_loop_end() && io_napi_busy_loop()) >> >>      ; >> >> >> Btw, start_time seems not used in singular branch. > Hao, > > it takes me few readings before being able to figure out the idea > behind your suggestions. Sorry about that! > > So, if I get it correctly, you are proposing extract out the singular > block out of the while loop... > > IMHO, this is not a good idea because you could start iterating the > do/while loop with a multiple entries list that ends up becoming a > singular list after one or few iterations. My bad, I get your point now. > > Check what io_napi_busy_loop() is doing... > > It does not look like that but a lot thoughts have been put into > writing io_blocking_napi_busy_loop()... True.