From patchwork Tue May 24 13:39:11 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Peter Lieven X-Patchwork-Id: 9133675 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id A0E3F607D3 for ; Tue, 24 May 2016 13:39:52 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 886C92821B for ; Tue, 24 May 2016 13:39:52 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 7D1462824F; Tue, 24 May 2016 13:39:52 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 9E0492821B for ; Tue, 24 May 2016 13:39:51 +0000 (UTC) Received: from localhost ([::1]:53418 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b5CYo-0004Xu-Qb for patchwork-qemu-devel@patchwork.kernel.org; Tue, 24 May 2016 09:39:50 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:44194) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b5CYT-0004Vi-6w for qemu-devel@nongnu.org; Tue, 24 May 2016 09:39:30 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1b5CYP-0003AC-GC for qemu-devel@nongnu.org; Tue, 24 May 2016 09:39:28 -0400 Received: from mx-v6.kamp.de ([2a02:248:0:51::16]:32991 helo=mx01.kamp.de) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b5CYP-00039m-6O for qemu-devel@nongnu.org; Tue, 24 May 2016 09:39:25 -0400 Received: (qmail 18295 invoked by uid 89); 24 May 2016 13:39:22 -0000 Received: from [195.62.97.28] by client-16-kamp (envelope-from , uid 89) with qmail-scanner-2010/03/19-MF (clamdscan: 0.99.2/21602. hbedv: 8.3.40.20/7.12.93.66. avast: 1.2.2/16052401. spamassassin: 3.4.1. Clear:RC:1(195.62.97.28):. Processed in 0.10179 secs); 24 May 2016 13:39:22 -0000 Received: from smtp.kamp.de (HELO submission.kamp.de) ([195.62.97.28]) by mx01.kamp.de with ESMTPS (DHE-RSA-AES256-GCM-SHA384 encrypted); 24 May 2016 13:39:21 -0000 X-GL_Whitelist: yes Received: (qmail 7751 invoked from network); 24 May 2016 13:39:21 -0000 Received: from lieven-pc.kamp-intra.net (HELO lieven-pc) (relay@kamp.de@::ffff:172.21.12.60) by submission.kamp.de with ESMTPS (DHE-RSA-AES256-GCM-SHA384 encrypted) ESMTPA; 24 May 2016 13:39:21 -0000 Received: by lieven-pc (Postfix, from userid 1000) id 2A40420435; Tue, 24 May 2016 15:39:21 +0200 (CEST) From: Peter Lieven To: qemu-block@nongnu.org Date: Tue, 24 May 2016 15:39:11 +0200 Message-Id: <1464097151-19479-1-git-send-email-pl@kamp.de> X-Mailer: git-send-email 1.9.1 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 2a02:248:0:51::16 Subject: [Qemu-devel] [PATCH] block/io: optimize bdrv_co_pwritev for small requests X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, famz@redhat.com, Peter Lieven , qemu-devel@nongnu.org, mreitz@redhat.com, stefanha@redhat.com Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" X-Virus-Scanned: ClamAV using ClamSMTP in a read-modify-write cycle a small request might cause head and tail to fall into the same alignment. Currently QEMU reads the same block twice in this case which is not necessary. Signed-off-by: Peter Lieven --- block/io.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/block/io.c b/block/io.c index 60a6bd8..fa40121 100644 --- a/block/io.c +++ b/block/io.c @@ -1430,6 +1430,18 @@ int coroutine_fn bdrv_co_pwritev(BlockDriverState *bs, bytes += offset & (align - 1); offset = offset & ~(align - 1); + + /* if head and tail fall into the same alignment + * we can omit the second read as it would read + * the same block again */ + if ((offset + bytes) & (align - 1) && + offset / align == (offset + bytes) / align) { + size_t tail_offs; + tail_offs = (offset + bytes) & (align - 1); + qemu_iovec_add(&local_qiov, head_buf + tail_offs, + align - tail_offs); + bytes += align - tail_offs; + } } if ((offset + bytes) & (align - 1)) {