From patchwork Thu Sep 12 13:46:04 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kevin Wolf X-Patchwork-Id: 11143139 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 41E70112B for ; Thu, 12 Sep 2019 14:05:35 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 22E0420856 for ; Thu, 12 Sep 2019 14:05:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 22E0420856 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Received: from localhost ([::1]:34864 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i8Pj3-0005WO-Hv for patchwork-qemu-devel@patchwork.kernel.org; Thu, 12 Sep 2019 10:05:33 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:39507) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i8PR8-0003Gq-RB for qemu-devel@nongnu.org; Thu, 12 Sep 2019 09:47:04 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i8PR7-0001d5-Jh for qemu-devel@nongnu.org; Thu, 12 Sep 2019 09:47:02 -0400 Received: from mx1.redhat.com ([209.132.183.28]:59418) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1i8PR5-0001ag-0g; Thu, 12 Sep 2019 09:46:59 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 4C7A2308421A; Thu, 12 Sep 2019 13:46:58 +0000 (UTC) Received: from linux.fritz.box.com (ovpn-116-179.ams2.redhat.com [10.36.116.179]) by smtp.corp.redhat.com (Postfix) with ESMTP id 3DE38600C8; Thu, 12 Sep 2019 13:46:57 +0000 (UTC) From: Kevin Wolf To: qemu-block@nongnu.org Date: Thu, 12 Sep 2019 15:46:04 +0200 Message-Id: <20190912134604.22019-23-kwolf@redhat.com> In-Reply-To: <20190912134604.22019-1-kwolf@redhat.com> References: <20190912134604.22019-1-kwolf@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.40]); Thu, 12 Sep 2019 13:46:58 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [PULL 22/22] qcow2: Stop overwriting compressed clusters one by one X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, peter.maydell@linaro.org, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" From: Alberto Garcia handle_alloc() tries to find as many contiguous clusters that need copy-on-write as possible in order to allocate all of them at the same time. However, compressed clusters are only overwritten one by one, so let's say that we have an image with 1024 consecutive compressed clusters: qemu-img create -f qcow2 hd.qcow2 64M for f in `seq 0 64 65472`; do qemu-io -c "write -c ${f}k 64k" hd.qcow2 done In this case trying to overwrite the whole image with one large write request results in 1024 separate allocations: qemu-io -c "write 0 64M" hd.qcow2 This restriction comes from commit 095a9c58ce12afeeb90c2 from 2008. Nowadays QEMU can overwrite multiple compressed clusters just fine, and in fact it already does: as long as the first cluster that handle_alloc() finds is not compressed, all other compressed clusters in the same batch will be overwritten in one go: qemu-img create -f qcow2 hd.qcow2 64M qemu-io -c "write -z 0 64k" hd.qcow2 for f in `seq 64 64 65472`; do qemu-io -c "write -c ${f}k 64k" hd.qcow2 done Compared to the previous one, overwriting this image on my computer goes from 8.35s down to 230ms. Signed-off-by: Alberto Garcia Reviewed-by: John Snow --- block/qcow2-cluster.c | 8 +------- 1 file changed, 1 insertion(+), 7 deletions(-) diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c index f09cc992af..dcacd3c450 100644 --- a/block/qcow2-cluster.c +++ b/block/qcow2-cluster.c @@ -1351,13 +1351,7 @@ static int handle_alloc(BlockDriverState *bs, uint64_t guest_offset, } entry = be64_to_cpu(l2_slice[l2_index]); - - /* For the moment, overwrite compressed clusters one by one */ - if (entry & QCOW_OFLAG_COMPRESSED) { - nb_clusters = 1; - } else { - nb_clusters = count_cow_clusters(bs, nb_clusters, l2_slice, l2_index); - } + nb_clusters = count_cow_clusters(bs, nb_clusters, l2_slice, l2_index); /* This function is only called when there were no non-COW clusters, so if * we can't find any unallocated or COW clusters either, something is