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=-15.3 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, 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 29ABBC4361A for ; Wed, 3 Mar 2021 06:51:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EBA1564E75 for ; Wed, 3 Mar 2021 06:51:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1350272AbhCCGo3 (ORCPT ); Wed, 3 Mar 2021 01:44:29 -0500 Received: from out30-42.freemail.mail.aliyun.com ([115.124.30.42]:52290 "EHLO out30-42.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244144AbhCCDD1 (ORCPT ); Tue, 2 Mar 2021 22:03:27 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R591e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04395;MF=jefflexu@linux.alibaba.com;NM=1;PH=DS;RN=10;SR=0;TI=SMTPD_---0UQAbNuR_1614740007; Received: from admindeMacBook-Pro-2.local(mailfrom:jefflexu@linux.alibaba.com fp:SMTPD_---0UQAbNuR_1614740007) by smtp.aliyun-inc.com(127.0.0.1); Wed, 03 Mar 2021 10:53:27 +0800 Subject: Re: [dm-devel] [PATCH 4/4] dm: support I/O polling To: Mikulas Patocka , Mike Snitzer , Heinz Mauelshagen , axboe@kernel.dk, caspar@linux.alibaba.com, io-uring@vger.kernel.org, linux-block@vger.kernel.org, joseph.qi@linux.alibaba.com, dm-devel@redhat.com, hch@lst.de References: <20210302190555.201228400@debian-a64.vm> From: JeffleXu Message-ID: <33fa121a-88a8-5c27-0a43-a7efc9b5b3e3@linux.alibaba.com> Date: Wed, 3 Mar 2021 10:53:27 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: <20210302190555.201228400@debian-a64.vm> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 3/3/21 3:05 AM, Mikulas Patocka wrote: > Support I/O polling if submit_bio_noacct_mq_direct returned non-empty > cookie. > > Signed-off-by: Mikulas Patocka > > --- > drivers/md/dm.c | 5 +++++ > 1 file changed, 5 insertions(+) > > Index: linux-2.6/drivers/md/dm.c > =================================================================== > --- linux-2.6.orig/drivers/md/dm.c 2021-03-02 19:26:34.000000000 +0100 > +++ linux-2.6/drivers/md/dm.c 2021-03-02 19:26:34.000000000 +0100 > @@ -1682,6 +1682,11 @@ static void __split_and_process_bio(stru > } > } > > + if (ci.poll_cookie != BLK_QC_T_NONE) { > + while (atomic_read(&ci.io->io_count) > 1 && > + blk_poll(ci.poll_queue, ci.poll_cookie, true)) ; > + } > + > /* drop the extra reference count */ > dec_pending(ci.io, errno_to_blk_status(error)); > } It seems that the general idea of your design is to 1) submit *one* split bio 2) blk_poll(), waiting the previously submitted split bio complets and then submit next split bio, repeating the above process. I'm afraid the performance may be an issue here, since the batch every time blk_poll() reaps may decrease. Besides, the submitting routine and polling routine is bound together here, i.e., polling is always synchronous. -- Thanks, Jeffle