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=-17.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, 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 A8DDDC433E6 for ; Thu, 4 Mar 2021 15:15:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 843F564F9F for ; Thu, 4 Mar 2021 15:15:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233928AbhCDPO2 (ORCPT ); Thu, 4 Mar 2021 10:14:28 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:26445 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233923AbhCDPOQ (ORCPT ); Thu, 4 Mar 2021 10:14:16 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1614870770; 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=1PKccDZxJZzWf6UmdzAmg+0FIgtiX2+VOvVVUPxQTIc=; b=gmZFLVkOlW/d2pa9Y/wm2dAg8fbNxqFkmGjbjflGnOT0eiZ9zRjQ8NB4w/NPVP/F7Hvzb3 REjnapk383zLZuHF16VOQB5D3ewTCWPFtOJ5boo214BHC4kVXpIDe8DvHiW8CM5fx17Vup KXVq4crICyvLotkqmISyKFaBhZwyZcw= 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-482-1E2bZhY3MzeKp9yjMtNiIQ-1; Thu, 04 Mar 2021 10:12:44 -0500 X-MC-Unique: 1E2bZhY3MzeKp9yjMtNiIQ-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 76EB21018F70; Thu, 4 Mar 2021 15:12:43 +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 5FED860CCB; Thu, 4 Mar 2021 15:12:40 +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 124FCdF3007183; Thu, 4 Mar 2021 10:12:39 -0500 Received: from localhost (mpatocka@localhost) by file01.intranet.prod.int.rdu2.redhat.com (8.14.4/8.14.4/Submit) with ESMTP id 124FCdDr007179; Thu, 4 Mar 2021 10:12:39 -0500 X-Authentication-Warning: file01.intranet.prod.int.rdu2.redhat.com: mpatocka owned process doing -bs Date: Thu, 4 Mar 2021 10:12:39 -0500 (EST) From: Mikulas Patocka X-X-Sender: mpatocka@file01.intranet.prod.int.rdu2.redhat.com To: Jeff Moyer cc: JeffleXu , 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 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Thu, 4 Mar 2021, Jeff Moyer wrote: > Hi, Mikulas, > > Mikulas Patocka writes: > > > On Wed, 3 Mar 2021, JeffleXu wrote: > > > >> > >> > >> 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 > > > > No, I submit all the bios and poll for the last one. > > What happens if the last bio completes first? It looks like you will > call blk_poll with a cookie that already completed, and I'm pretty sure > that's invalid. > > Thanks, > Jeff If the last bio completes first, the other bios will use interrupt-driven endio. Calling blk_poll with already completed cookie is IMHO legal - it happens with the current direct-io code too. The direct-io code will check for bio completion and if the bio is not completed, call blk_poll. The bio may be completed from an interrupt after the check and before blk_poll - in this case, we will call blk_poll with already completed cookie. Mikulas