From nobody Sun Feb 8 18:57:33 2026 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) client-ip=208.118.235.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org Return-Path: Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) by mx.zohomail.com with SMTPS id 1499961416237632.3023058469636; Thu, 13 Jul 2017 08:56:56 -0700 (PDT) Received: from localhost ([::1]:60848 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dVgU3-0006Zc-3R for importer@patchew.org; Thu, 13 Jul 2017 11:56:55 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:54338) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dVgM1-0005xB-Tp for qemu-devel@nongnu.org; Thu, 13 Jul 2017 11:48:39 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dVgM0-0006Hu-V9 for qemu-devel@nongnu.org; Thu, 13 Jul 2017 11:48:37 -0400 Received: from mx1.redhat.com ([209.132.183.28]:1366) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dVgLw-0006EC-4Z; Thu, 13 Jul 2017 11:48:32 -0400 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id EFE5D83F44; Thu, 13 Jul 2017 15:48:30 +0000 (UTC) Received: from red.redhat.com (ovpn-121-60.rdu2.redhat.com [10.10.121.60]) by smtp.corp.redhat.com (Postfix) with ESMTP id 94E4D70A03; Thu, 13 Jul 2017 15:48:15 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com EFE5D83F44 Authentication-Results: ext-mx03.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx03.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=eblake@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com EFE5D83F44 From: Eric Blake To: qemu-devel@nongnu.org Date: Thu, 13 Jul 2017 10:47:02 -0500 Message-Id: <20170713154711.32374-15-eblake@redhat.com> In-Reply-To: <20170713154711.32374-1-eblake@redhat.com> References: <20170713154711.32374-1-eblake@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Thu, 13 Jul 2017 15:48:31 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [PATCH v3 14/23] qemu-img: Speed up compare on pre-allocated larger file 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, qemu-block@nongnu.org, el13635@mail.ntua.gr, Max Reitz , jsnow@redhat.com Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail: RSF_0 Z_629925259 SPT_0 Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Compare the following images with all-zero contents: $ truncate --size 1M A $ qemu-img create -f qcow2 -o preallocation=3Doff B 1G $ qemu-img create -f qcow2 -o preallocation=3Dmetadata C 1G On my machine, the difference is noticeable for pre-patch speeds, with more than an order of magnitude in difference caused by the choice of preallocation in the qcow2 file: $ time ./qemu-img compare -f raw -F qcow2 A B Warning: Image size mismatch! Images are identical. real 0m0.014s user 0m0.007s sys 0m0.007s $ time ./qemu-img compare -f raw -F qcow2 A C Warning: Image size mismatch! Images are identical. real 0m0.341s user 0m0.144s sys 0m0.188s Why? Because bdrv_is_allocated() returns false for image B but true for image C, throwing away the fact that both images know via lseek(SEEK_HOLE) that the entire image still reads as zero. From there, qemu-img ends up calling bdrv_pread() for every byte of the tail, instead of quickly looking for the next allocation. The solution: use block_status instead of is_allocated, giving: $ time ./qemu-img compare -f raw -F qcow2 A C Warning: Image size mismatch! Images are identical. real 0m0.014s user 0m0.011s sys 0m0.003s which is on par with the speeds for no pre-allocation. Signed-off-by: Eric Blake --- v3: new patch --- qemu-img.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/qemu-img.c b/qemu-img.c index bc21d00..46f9da5 100644 --- a/qemu-img.c +++ b/qemu-img.c @@ -1471,11 +1471,11 @@ static int img_compare(int argc, char **argv) while (sector_num < progress_base) { int64_t count; - ret =3D bdrv_is_allocated_above(blk_bs(blk_over), NULL, + ret =3D bdrv_block_status_above(blk_bs(blk_over), NULL, sector_num * BDRV_SECTOR_SIZE, (progress_base - sector_num) * BDRV_SECTOR_SIZE, - &count); + &count, NULL); if (ret < 0) { ret =3D 3; error_report("Sector allocation test failed for %s", @@ -1483,11 +1483,11 @@ static int img_compare(int argc, char **argv) goto out; } - /* TODO relax this once bdrv_is_allocated_above does not enfor= ce + /* TODO relax this once bdrv_block_status_above does not enfor= ce * sector alignment */ assert(QEMU_IS_ALIGNED(count, BDRV_SECTOR_SIZE)); nb_sectors =3D count >> BDRV_SECTOR_BITS; - if (ret) { + if (ret & BDRV_BLOCK_ALLOCATED && !(ret & BDRV_BLOCK_ZERO)) { nb_sectors =3D MIN(nb_sectors, IO_BUF_SIZE >> BDRV_SECTOR_= BITS); ret =3D check_empty_sectors(blk_over, sector_num, nb_secto= rs, filename_over, buf1, quiet); --=20 2.9.4