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=-7.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 A625EC433DB for ; Thu, 4 Mar 2021 10:11:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6F2FE64F21 for ; Thu, 4 Mar 2021 10:11:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233700AbhCDKLL (ORCPT ); Thu, 4 Mar 2021 05:11:11 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:20709 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233357AbhCDKLA (ORCPT ); Thu, 4 Mar 2021 05:11:00 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1614852575; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=gEq80ZVZMwjKodIE6ojiKHKFbahisMaPtzK8j1T5l58=; b=AUe0w1sOD5CPZk8qtMHUrECy5TVTlJ0zIZiondKw+wogxt1KpduE8NH9J+Al230a9/pnqd UrTIAqmO0sYzeMP4iCfNXuf8ZJno5kF+QbDV79H7PhvW3gRozaPB9JdX+eAXT4N7HadnQh 8af+CUGs8TRFC+cZTEWqaJ81a/rov5A= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-515-TTouH1leOkqqT0-g4BvVzw-1; Thu, 04 Mar 2021 05:09:31 -0500 X-MC-Unique: TTouH1leOkqqT0-g4BvVzw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id F2EA71005D4A; Thu, 4 Mar 2021 10:09:29 +0000 (UTC) Received: from file01.intranet.prod.int.rdu2.redhat.com (file01.intranet.prod.int.rdu2.redhat.com [10.11.5.7]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 47364100E114; Thu, 4 Mar 2021 10:09:26 +0000 (UTC) Received: from file01.intranet.prod.int.rdu2.redhat.com (localhost [127.0.0.1]) by file01.intranet.prod.int.rdu2.redhat.com (8.14.4/8.14.4) with ESMTP id 124A9PQ9007649; Thu, 4 Mar 2021 05:09:25 -0500 Received: from localhost (mpatocka@localhost) by file01.intranet.prod.int.rdu2.redhat.com (8.14.4/8.14.4/Submit) with ESMTP id 124A9Oo8007645; Thu, 4 Mar 2021 05:09:25 -0500 X-Authentication-Warning: file01.intranet.prod.int.rdu2.redhat.com: mpatocka owned process doing -bs Date: Thu, 4 Mar 2021 05:09:24 -0500 (EST) From: Mikulas Patocka X-X-Sender: mpatocka@file01.intranet.prod.int.rdu2.redhat.com To: JeffleXu cc: 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 Subject: Re: [dm-devel] [PATCH 4/4] dm: support I/O polling In-Reply-To: Message-ID: References: <20210302190555.201228400@debian-a64.vm> <33fa121a-88a8-5c27-0a43-a7efc9b5b3e3@linux.alibaba.com> User-Agent: Alpine 2.02 (LRH 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Thu, 4 Mar 2021, JeffleXu wrote: > > __split_and_process_non_flush records the poll cookie in ci.poll_cookie. > > When we processed all the bios, we poll for the last cookie here: > > > > 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)) ; > > } > > So what will happen if one bio submitted to dm device crosses the device > boundary among several target devices (e.g., dm-stripe)? Please refer > the following call graph. > > ``` > submit_bio > __submit_bio_noacct > disk->fops->submit_bio(), calling into __split_and_process_bio(), > call __split_and_process_non_flush() once, submitting the *first* split bio > disk->fops->submit_bio(), calling into __split_and_process_bio(), > call __split_and_process_non_flush() once, submitting the *second* split bio > ... > ``` > > > So the loop is in __submit_bio_noacct(), rather than > __split_and_process_bio(). Your design will send the first split bio, > and then poll on this split bio, then send the next split bio, polling > on this, go on and on... No. It will send all the bios and poll for the last one. Mikulas