From patchwork Mon Jun 22 15:12:03 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kevin Wolf X-Patchwork-Id: 11618181 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 44F5914B7 for ; Mon, 22 Jun 2020 15:22:12 +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 1A5B9206D7 for ; Mon, 22 Jun 2020 15:22:12 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="cWjYTA3U" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1A5B9206D7 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]:33558 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jnOGx-0002Vg-AM for patchwork-qemu-devel@patchwork.kernel.org; Mon, 22 Jun 2020 11:22:11 -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 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= 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 X-MC-Unique: wjSteQknO2OK6vy50U3u1A-1 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) 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 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+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" 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 = bdrv_has_zero_init(blk_bs(s->target)); } - if (!s->has_zero_init && !s->target_has_backing && - bdrv_can_write_zeroes_with_unmap(blk_bs(s->target))) - { - ret = blk_make_zero(s->target, BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK); - if (ret == 0) { - s->has_zero_init = true; - } - } - /* Allocate buffer for copied data. For compressed images, only one cluster * can be copied at a time. */ if (s->compressed) {