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=-6.1 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 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 E9E25C48BE5 for ; Mon, 21 Jun 2021 08:42:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CCB92611C1 for ; Mon, 21 Jun 2021 08:42:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229789AbhFUIoV (ORCPT ); Mon, 21 Jun 2021 04:44:21 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:54534 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229618AbhFUIoU (ORCPT ); Mon, 21 Jun 2021 04:44:20 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1624264926; 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=5sbzr9XPq1LgidDaQqIaLaDJS9KPyp6a/zru6azg0dE=; b=Wrwf0KXG65iqyMj8PHErL3dGxaMk+IWLpmNY0IzWKx1hLtrfxRUbiImFjAixgqVzhGcrFc XXkDvwljd1LMeLtOsYB01tgV/6AK6Twk1WpIwJULFJ2iN9nEKI3Xli4FMg3yF1fGkR6hD4 1vZH9LZ7Se3TaaYqdB0H957XPiTArjs= 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-261-RrT0RfK4MNml5i07-kcRMQ-1; Mon, 21 Jun 2021 04:42:05 -0400 X-MC-Unique: RrT0RfK4MNml5i07-kcRMQ-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id F1A9B800C60; Mon, 21 Jun 2021 08:42:03 +0000 (UTC) Received: from T590 (ovpn-13-237.pek2.redhat.com [10.72.13.237]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 514791ABD4; Mon, 21 Jun 2021 08:41:50 +0000 (UTC) Date: Mon, 21 Jun 2021 16:41:33 +0800 From: Ming Lei To: Christoph Hellwig Cc: Jens Axboe , Mike Snitzer , linux-block@vger.kernel.org, Jeffle Xu , dm-devel@redhat.com, Hannes Reinecke Subject: Re: [RFC PATCH V2 2/3] block: add ->poll_bio to block_device_operations Message-ID: References: <20210617103549.930311-1-ming.lei@redhat.com> <20210617103549.930311-3-ming.lei@redhat.com> <20210621072502.GC6651@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210621072502.GC6651@lst.de> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Mon, Jun 21, 2021 at 09:25:02AM +0200, Christoph Hellwig wrote: > > + struct gendisk *disk = bio->bi_bdev->bd_disk; > > + struct request_queue *q = disk->queue; > > blk_qc_t cookie = READ_ONCE(bio->bi_cookie); > > int ret; > > > > - if (cookie == BLK_QC_T_NONE || !blk_queue_poll(q)) > > + if ((queue_is_mq(q) && cookie == BLK_QC_T_NONE) || > > + !blk_queue_poll(q)) > > return 0; > > How does polling for a bio without a cookie make sense even when > polling bio based? It isn't necessary to use bio->bi_cookie, that is why I doesn't use it, which actually provides one free 32bit in bio for bio based driver. > > But if we come up for a good rationale for this I'd really > split the conditions to make them more readable: > > if (!test_bit(QUEUE_FLAG_POLL, &q->queue_flags)) > return 0; > if (queue_is_mq(q) && cookie == BLK_QC_T_NONE) > return 0; OK. > > > + if (!queue_is_mq(q)) { > > + if (disk->fops->poll_bio) { > > + ret = disk->fops->poll_bio(bio, flags); > > + } else { > > + WARN_ON_ONCE(1); > > + ret = 0; > > + } > > + } else { > > ret = blk_mq_poll(q, cookie, flags); > > I'd go for someting like: > > if (queue_is_mq(q)) > ret = blk_mq_poll(q, cookie, flags); > else if (disk->fops->poll_bio) > ret = disk->fops->poll_bio(bio, flags); > else > WARN_ON_ONCE(1); > > with ret initialized to 0 at declaration time. Fine. > > > struct block_device_operations { > > void (*submit_bio)(struct bio *bio); > > + /* ->poll_bio is for bio driver only */ > > I'd drop the comment, this is already nicely documented in add_disk > together with the actual check. We also don't note this for submit_bio > here. OK. thanks, Ming