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=-5.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 71D9BCA9ECF for ; Fri, 1 Nov 2019 12:41:49 +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 3B6942067D for ; Fri, 1 Nov 2019 12:41:49 +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="TpX1Wog8" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3B6942067D 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+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:38736 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iQWFQ-0006KU-Ae for qemu-devel@archiver.kernel.org; Fri, 01 Nov 2019 08:41:48 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:42046) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iQWEO-0005Z0-Lu for qemu-devel@nongnu.org; Fri, 01 Nov 2019 08:40:45 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iQWEL-0006Lj-QZ for qemu-devel@nongnu.org; Fri, 01 Nov 2019 08:40:43 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:40300 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iQWEJ-0006De-RX for qemu-devel@nongnu.org; Fri, 01 Nov 2019 08:40:40 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1572612034; 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: in-reply-to:in-reply-to:references:references; bh=zk74v0gC+DNvjMBYuOPhBn7nW4PGZ3x2jINkHxEweO4=; b=TpX1Wog8X3A6vLilixjBXKE147Mts3wu4MKg0tJbXbQDuFQZFveykfp/uSbnMyXr0Ek/+I utOKcRzBE9OxoqJQF9jPyUFqpduwfZ/LRto2xpq1P0iCSsLmYPVmOHyyxzWZOI3BTuICIC xkwsAMKNH7rBjn4LKPJSx5VRnK8vV2M= 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-212-DmbTG27MOY2yevXaN8VelA-1; Fri, 01 Nov 2019 08:40:30 -0400 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 565CA800C77; Fri, 1 Nov 2019 12:40:29 +0000 (UTC) Received: from [10.3.116.202] (ovpn-116-202.phx2.redhat.com [10.3.116.202]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 9A74F1001B32; Fri, 1 Nov 2019 12:40:24 +0000 (UTC) Subject: Re: [PATCH for-4.2 1/4] Revert "qcow2: skip writing zero buffers to empty COW areas" To: Max Reitz , qemu-block@nongnu.org References: <20191101100019.9512-1-mreitz@redhat.com> <20191101100019.9512-2-mreitz@redhat.com> From: Eric Blake Organization: Red Hat, Inc. Message-ID: Date: Fri, 1 Nov 2019 13:40:23 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <20191101100019.9512-2-mreitz@redhat.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-MC-Unique: DmbTG27MOY2yevXaN8VelA-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=WINDOWS-1252; format=flowed Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 205.139.110.61 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 , Anton Nefedov , Vladimir Sementsov-Ogievskiy , qemu-devel@nongnu.org, Stefan Hajnoczi Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 11/1/19 11:00 AM, Max Reitz wrote: > This reverts commit c8bb23cbdbe32f5c326365e0a82e1b0e68cdcd8a. >=20 > This commit causes fundamental performance problems on XFS (because > fallocate() stalls the AIO pipeline), and as such it is not clear that > we should unconditionally enable this behavior. >=20 > We expect subclusters to alleviate the performance penalty of small > writes to newly allocated clusters, so when we get them, the originally > intended performance gain may actually no longer be significant. >=20 > If we want to reintroduce something similar to c8bb23cbdbe, it will > require extensive benchmarking on various systems with subclusters > enabled. >=20 > Cc: qemu-stable@nongnu.org > Signed-off-by: Max Reitz > --- > +++ b/qapi/block-core.json > @@ -3304,8 +3304,6 @@ > # > # @cor_write: a write due to copy-on-read (since 2.11) > # > -# @cluster_alloc_space: an allocation of file space for a cluster (since= 4.1) > -# > # @none: triggers once at creation of the blkdebug node (since 4.1) Deleting released qapi is not backwards-compatible. However, given that=20 the only known user of this interface is debug testing via iotests, I'm=20 not too concerned that we would be impacting any external users. --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org