From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CA4D7C4338F for ; Tue, 3 Aug 2021 15:04:28 +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 30E476103C for ; Tue, 3 Aug 2021 15:04:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 30E476103C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=nongnu.org Received: from localhost ([::1]:39742 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mAvxz-0006go-0d for qemu-devel@archiver.kernel.org; Tue, 03 Aug 2021 11:04:27 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:38142) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mAvx5-0005sc-P3 for qemu-devel@nongnu.org; Tue, 03 Aug 2021 11:03:31 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:34165) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mAvx4-0002UL-Cx for qemu-devel@nongnu.org; Tue, 03 Aug 2021 11:03:31 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1628003009; 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: in-reply-to:in-reply-to:references:references; bh=mxjxKRpNMC6AuQ+8yrfMQ+2QHboOhpGlmI6R5XBq1Yg=; b=VzidJM8XeHSAe4GkPAGStzJOWmzLHjWH9A2m22kJYJoHN5ude1NPODfFVLYSSJQzgKPUkx WDBAH3NFTZsBEdhuaJoPKULA3g8SAeFdAyZ2rBaHYCM0tB0P/KkVpMH6NJFkWgk3sRAePG cgCp/Aqnd4tOsCGckvIwirbs3Rj507k= 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-189-vUW9c1Z5PiGEXs4w4Shp_Q-1; Tue, 03 Aug 2021 11:03:20 -0400 X-MC-Unique: vUW9c1Z5PiGEXs4w4Shp_Q-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 73296192CC43; Tue, 3 Aug 2021 15:03:19 +0000 (UTC) Received: from redhat.com (ovpn-114-4.phx2.redhat.com [10.3.114.4]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8E72C779D0; Tue, 3 Aug 2021 15:03:18 +0000 (UTC) Date: Tue, 3 Aug 2021 10:03:16 -0500 From: Eric Blake To: Zhenyu Ye Subject: Re: [Question] qemu-img convert block alignment Message-ID: <20210803150316.eo5gm3xqxuetqahq@redhat.com> References: MIME-Version: 1.0 In-Reply-To: User-Agent: NeoMutt/20210205-687-0ed190 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=eblake@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.699, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no 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: Kevin Wolf , pl@kamp.de, qemu-devel@nongnu.org, qemu-block@nongnu.org, mreitz@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Apr 02, 2021 at 11:52:25AM +0800, Zhenyu Ye wrote: > Hi all, > > commit 8dcd3c9b91 ("qemu-img: align result of is_allocated_sectors") > introduces block alignment when doing qemu-img convert. However, the > alignment is: > > s.alignment = MAX(pow2floor(s.min_sparse), > DIV_ROUND_UP(out_bs->bl.request_alignment, > BDRV_SECTOR_SIZE)); > > (where the default s.min_sparse is 8) > When the target device's bl.request_alignment is smaller than 4K, this > will cause additional write-zero overhead and makes the size of target > file larger. > > Is this as expected? Should we change the MAX() to MIN()? Yes it is expected, and no we shouldn't change it. Even when a target advertises a bl.request_alignment of 512, our goal is to avoid needing read-modify-write cycles when that target is really on top of a 4k sector disk. Writing extra 0s out to the 4k boundaries does not change the fact that allocation is in 4k chunks anyways, regardless of whether the disk supports smaller 512-byte reads. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org