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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id BAF39CCA476 for ; Fri, 10 Oct 2025 16:35:56 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1v7G4G-0001B1-UD; Fri, 10 Oct 2025 12:34:09 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1v7G4E-0001AF-LB for qemu-devel@nongnu.org; Fri, 10 Oct 2025 12:34:06 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1v7G45-0008SD-Ij for qemu-devel@nongnu.org; Fri, 10 Oct 2025 12:34:05 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1760114035; 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=K7AIhbAJqO/829X4D014/CHO6xh8D/I6myRXwqtt09o=; b=LXjouX2urs17qtvv2iJ+Gi3l/+rfign3rnxzZwvXUWwuzQrA6rojXi3NQKgpsq9LKJz7OL 4IAk36hNqUoyz4KS1AtjIPLsFF7C96oJh4BLiy8rBQa000c58+yGparuEWV4ilR3ZFUx2e R/ZmgmCFlE3mDCV/9DmjBU1QRvx6s20= Received: from mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-246-KM8eVfJRM6CYq-TBOz8iOQ-1; Fri, 10 Oct 2025 12:33:49 -0400 X-MC-Unique: KM8eVfJRM6CYq-TBOz8iOQ-1 X-Mimecast-MFC-AGG-ID: KM8eVfJRM6CYq-TBOz8iOQ_1760114028 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 5F5A119560B5; Fri, 10 Oct 2025 16:33:47 +0000 (UTC) Received: from redhat.com (unknown [10.45.224.92]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id AC5741800576; Fri, 10 Oct 2025 16:33:43 +0000 (UTC) Date: Fri, 10 Oct 2025 18:33:40 +0200 From: Kevin Wolf To: Stefan Hajnoczi Cc: qemu-devel@nongnu.org, Aarushi Mehta , Fam Zheng , Stefano Garzarella , Hanna Czenczek , eblake@redhat.com, qemu-block@nongnu.org, hibriansong@gmail.com, Stefan Weil , Paolo Bonzini Subject: Re: [PATCH v4 12/12] block/io_uring: use non-vectored read/write when possible Message-ID: References: <20250910175703.374499-1-stefanha@redhat.com> <20250910175703.374499-13-stefanha@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250910175703.374499-13-stefanha@redhat.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 Received-SPF: pass client-ip=170.10.133.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.441, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Am 10.09.2025 um 19:57 hat Stefan Hajnoczi geschrieben: > The io_uring_prep_readv2/writev2() man pages recommend using the > non-vectored read/write operations when possible for performance > reasons. > > I didn't measure a significant difference but it doesn't hurt to have > this optimization in place. > > Suggested-by: Eric Blake > Signed-off-by: Stefan Hajnoczi > --- > block/io_uring.c | 29 ++++++++++++++++++++++++----- > 1 file changed, 24 insertions(+), 5 deletions(-) > > diff --git a/block/io_uring.c b/block/io_uring.c > index dd930ee57e..bbefbddcc0 100644 > --- a/block/io_uring.c > +++ b/block/io_uring.c > @@ -49,12 +49,24 @@ static void luring_prep_sqe(struct io_uring_sqe *sqe, void *opaque) > #ifdef HAVE_IO_URING_PREP_WRITEV2 > { > int luring_flags = (flags & BDRV_REQ_FUA) ? RWF_DSYNC : 0; > - io_uring_prep_writev2(sqe, fd, qiov->iov, > - qiov->niov, offset, luring_flags); > + if (luring_flags != 0 || qiov->niov > 1) { > + io_uring_prep_writev2(sqe, fd, qiov->iov, > + qiov->niov, offset, luring_flags); > + } else { > + /* The man page says non-vectored is faster than vectored */ > + struct iovec *iov = qiov->iov; > + io_uring_prep_write(sqe, fd, iov->iov_base, iov->iov_len, offset); > + } > } > #else > assert(flags == 0); > - io_uring_prep_writev(sqe, fd, qiov->iov, qiov->niov, offset); > + if (qiov->niov > 1) { > + io_uring_prep_writev(sqe, fd, qiov->iov, qiov->niov, offset); > + } else { > + /* The man page says non-vectored is faster than vectored */ > + struct iovec *iov = qiov->iov; > + io_uring_prep_write(sqe, fd, iov->iov_base, iov->iov_len, offset); > + } > #endif We have a lot of duplication in this now. Let's use the #ifdef a little more locally: { int luring_flags = (flags & BDRV_REQ_FUA) ? RWF_DSYNC : 0; if (luring_flags != 0 || qiov->niov > 1) { #ifdef HAVE_IO_URING_PREP_WRITEV2 io_uring_prep_writev2(sqe, fd, qiov->iov, qiov->niov, offset, luring_flags); #else assert(luring_flags == 0); io_uring_prep_writev(sqe, fd, qiov->iov, qiov->niov, offset); #endif } else { /* The man page says non-vectored is faster than vectored */ struct iovec *iov = qiov->iov; io_uring_prep_write(sqe, fd, iov->iov_base, iov->iov_len, offset); } } Kevin