From nobody Fri May 3 08:06:33 2024 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; dkim=fail; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=redhat.com ARC-Seal: i=1; a=rsa-sha256; t=1592839359; cv=none; d=zohomail.com; s=zohoarc; b=Ivv8Rbfxp2Q5BY65/a19d6YVJhibQJvUuTgrzU4dVlUsmip0Ssc3iBBo9vuzqWuqf1j7o9ssh5J96sRPpJ4m5JfQ+z1GQT5726dgrgyhDsJcTrgUF2j/3/TSuOa6D6Z//5vH9KfpgED/fC6gBEZiDaLYJzGU8uJmy6buEmlqwtY= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1592839359; h=Content-Type:Content-Transfer-Encoding:Cc:Date:From:List-Subscribe:List-Post:List-Id:List-Archive:List-Help:List-Unsubscribe:MIME-Version:Message-ID:Sender:Subject:To; bh=BNvSGC9nTqGGUEXPC0RjFmoV3QN006CFzuU+WpDEcQc=; b=lRztE5ZhL6fPvDZSQwDfQZ6bkYT3eejpiRQSHPQHZtH6iZQXdGXdvTPY98Cs+GJvQpYzU+o7eD26daR61D4YNQyyXT/ZfXRwROpD875kac+nEl0Jom8jpXuj2TcDNxXUUvbnuUyltjK213fzbdywnOUNVc9ikKuiP8yUJEdzc5s= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=fail; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail header.from= (p=none dis=none) header.from= Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1592839359922899.8358380115499; Mon, 22 Jun 2020 08:22:39 -0700 (PDT) Received: from localhost ([::1]:33558 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jnOHO-0002Vg-I7 for importer@patchew.org; Mon, 22 Jun 2020 11:22:38 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:51128) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jnO7K-0000y5-TG for qemu-devel@nongnu.org; Mon, 22 Jun 2020 11:12:14 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:27852 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jnO7I-00066M-9s for qemu-devel@nongnu.org; Mon, 22 Jun 2020 11:12:14 -0400 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-454-wjSteQknO2OK6vy50U3u1A-1; Mon, 22 Jun 2020 11:12:10 -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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id 04A52A0BEB; Mon, 22 Jun 2020 15:12:09 +0000 (UTC) Received: from linux.fritz.box.com (ovpn-113-179.ams2.redhat.com [10.36.113.179]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5775471676; Mon, 22 Jun 2020 15:12:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1592838731; 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: content-transfer-encoding:content-transfer-encoding; bh=BNvSGC9nTqGGUEXPC0RjFmoV3QN006CFzuU+WpDEcQc=; b=cWjYTA3UOUbqoSjTDmI9R7TyksS35lhHJ7v02/MMKS3wyoHi740Ns8jClBmyHt/NyYY0M6 o03Gq8yrxghORpodi9izduMqOX6KRV0aqkFmwwusqZ+HVPx74B/cb/oDYMogDrZgORdaB1 xDs8BRBquDvPCjbsx/fzpEuWWNFw9EI= X-MC-Unique: wjSteQknO2OK6vy50U3u1A-1 From: Kevin Wolf To: qemu-block@nongnu.org Subject: [PATCH] qemu-img convert: Don't pre-zero images Date: Mon, 22 Jun 2020 17:12:03 +0200 Message-Id: <20200622151203.35624-1-kwolf@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=205.139.110.120; envelope-from=kwolf@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/22 01:27:42 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, 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=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action 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, pl@kamp.de, qemu-devel@nongnu.org, mreitz@redhat.com, nsoffer@redhat.com Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) Content-Type: text/plain; charset="utf-8" Since commit 5a37b60a61c, qemu-img create will pre-zero the target image if it isn't already zero-initialised (most importantly, for host block devices, but also iscsi etc.), so that writing explicit zeros wouldn't be necessary later. This could speed up the operation significantly, in particular when the source image file was only sparsely populated. However, it also means that some block are written twice: Once when pre-zeroing them, and then when they are overwritten with actual data. On a full image, the pre-zeroing is wasted work because everything will be overwritten. In practice, write_zeroes typically turns out faster than writing explicit zero buffers, but slow enough that first zeroing everything and then overwriting parts can be a significant net loss. Meanwhile, qemu-img convert was rewritten in 690c7301600 and zero blocks are now written to the target using bdrv_co_pwrite_zeroes() if the target could be pre-zeroed. This way we already make use of the faster write_zeroes operation, but avoid writing any blocks twice. Remove the pre-zeroing because these days this former optimisation has actually turned into a pessimisation in the common case. Reported-by: Nir Soffer Signed-off-by: Kevin Wolf Reviewed-by: Eric Blake --- qemu-img.c | 9 --------- 1 file changed, 9 deletions(-) diff --git a/qemu-img.c b/qemu-img.c index d7e846e607..bdb9f6aa46 100644 --- a/qemu-img.c +++ b/qemu-img.c @@ -2084,15 +2084,6 @@ static int convert_do_copy(ImgConvertState *s) s->has_zero_init =3D bdrv_has_zero_init(blk_bs(s->target)); } =20 - if (!s->has_zero_init && !s->target_has_backing && - bdrv_can_write_zeroes_with_unmap(blk_bs(s->target))) - { - ret =3D blk_make_zero(s->target, BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_= FALLBACK); - if (ret =3D=3D 0) { - s->has_zero_init =3D true; - } - } - /* Allocate buffer for copied data. For compressed images, only one cl= uster * can be copied at a time. */ if (s->compressed) { --=20 2.25.4