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Fri, 1 Nov 2019 14:01:07 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-117-28.ams2.redhat.com [10.36.117.28]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B3C845C28E; Fri, 1 Nov 2019 14:01:04 +0000 (UTC) Subject: Re: [PATCH for-4.2 1/4] Revert "qcow2: skip writing zero buffers to empty COW areas" To: Eric Blake , qemu-block@nongnu.org References: <20191101100019.9512-1-mreitz@redhat.com> <20191101100019.9512-2-mreitz@redhat.com> From: Max Reitz Autocrypt: addr=mreitz@redhat.com; prefer-encrypt=mutual; keydata= mQENBFXOJlcBCADEyyhOTsoa/2ujoTRAJj4MKA21dkxxELVj3cuILpLTmtachWj7QW+TVG8U /PsMCFbpwsQR7oEy8eHHZwuGQsNpEtNC2G/L8Yka0BIBzv7dEgrPzIu+W3anZXQW4702+uES U29G8TP/NGfXRRHGlbBIH9KNUnOSUD2vRtpOLXkWsV5CN6vQFYgQfFvmp5ZpPeUe6xNplu8V mcTw8OSEDW/ZnxJc8TekCKZSpdzYoxfzjm7xGmZqB18VFwgJZlIibt1HE0EB4w5GsD7x5ekh awIe3RwoZgZDLQMdOitJ1tUc8aqaxvgA4tz6J6st8D8pS//m1gAoYJWGwwIVj1DjTYLtABEB AAG0HU1heCBSZWl0eiA8bXJlaXR6QHJlZGhhdC5jb20+iQFTBBMBCAA9AhsDBQkSzAMABQsJ CAcCBhUICQoLAgQWAgMBAh4BAheABQJVzie5FRhoa3A6Ly9rZXlzLmdudXBnLm5ldAAKCRD0 B9sAYdXPQDcIB/9uNkbYEex1rHKz3mr12uxYMwLOOFY9fstP5aoVJQ1nWQVB6m2cfKGdcRe1 2/nFaHSNAzT0NnKz2MjhZVmcrpyd2Gp2QyISCfb1FbT82GMtXFj1wiHmPb3CixYmWGQUUh+I AvUqsevLA+WihgBUyaJq/vuDVM1/K9Un+w+Tz5vpeMidlIsTYhcsMhn0L9wlCjoucljvbDy/ 8C9L2DUdgi3XTa0ORKeflUhdL4gucWoAMrKX2nmPjBMKLgU7WLBc8AtV+84b9OWFML6NEyo4 4cP7cM/07VlJK53pqNg5cHtnWwjHcbpGkQvx6RUx6F1My3y52vM24rNUA3+ligVEgPYBuQEN BFXOJlcBCADAmcVUNTWT6yLWQHvxZ0o47KCP8OcLqD+67T0RCe6d0LP8GsWtrJdeDIQk+T+F xO7DolQPS6iQ6Ak2/lJaPX8L0BkEAiMuLCKFU6Bn3lFOkrQeKp3u05wCSV1iKnhg0UPji9V2 W5eNfy8F4ZQHpeGUGy+liGXlxqkeRVhLyevUqfU0WgNqAJpfhHSGpBgihUupmyUg7lfUPeRM DzAN1pIqoFuxnN+BRHdAecpsLcbR8sQddXmDg9BpSKozO/JyBmaS1RlquI8HERQoe6EynJhd 64aICHDfj61rp+/0jTIcevxIIAzW70IadoS/y3DVIkuhncgDBvGbF3aBtjrJVP+5ABEBAAGJ ASUEGAEIAA8FAlXOJlcCGwwFCRLMAwAACgkQ9AfbAGHVz0CbFwf9F/PXxQR9i4N0iipISYjU sxVdjJOM2TMut+ZZcQ6NSMvhZ0ogQxJ+iEQ5OjnIputKvPVd5U7WRh+4lF1lB/NQGrGZQ1ic alkj6ocscQyFwfib+xIe9w8TG1CVGkII7+TbS5pXHRxZH1niaRpoi/hYtgzkuOPp35jJyqT/ /ELbqQTDAWcqtJhzxKLE/ugcOMK520dJDeb6x2xVES+S5LXby0D4juZlvUj+1fwZu+7Io5+B bkhSVPb/QdOVTpnz7zWNyNw+OONo1aBUKkhq2UIByYXgORPFnbfMY7QWHcjpBVw9MgC4tGeF R4bv+1nAMMxKmb5VvQCExr0eFhJUAHAhVg== Message-ID: Date: Fri, 1 Nov 2019 15:01:02 +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: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Mimecast-Spam-Score: 0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="TEypAhPXNjarWQ1iAPmjC13PFAKCCuEda" X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 205.139.110.120 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" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --TEypAhPXNjarWQ1iAPmjC13PFAKCCuEda Content-Type: multipart/mixed; boundary="Ms7BYJ1fvZqURUh0mX06iL60AqIyyvjOt" --Ms7BYJ1fvZqURUh0mX06iL60AqIyyvjOt Content-Type: text/plain; charset=WINDOWS-1252 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 01.11.19 13:40, Eric Blake wrote: > On 11/1/19 11:00 AM, Max Reitz wrote: >> This reverts commit c8bb23cbdbe32f5c326365e0a82e1b0e68cdcd8a. >> >> 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. >> >> 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. >> >> If we want to reintroduce something similar to c8bb23cbdbe, it will >> require extensive benchmarking on various systems with subclusters >> enabled. >> >> Cc: qemu-stable@nongnu.org >> Signed-off-by: Max Reitz >> --- >=20 >> +++ b/qapi/block-core.json >> @@ -3304,8 +3304,6 @@ >> =A0 # >> =A0 # @cor_write: a write due to copy-on-read (since 2.11) >> =A0 # >> -# @cluster_alloc_space: an allocation of file space for a cluster >> (since 4.1) >> -# >> =A0 # @none: triggers once at creation of the blkdebug node (since 4.1) >=20 > Deleting released qapi is not backwards-compatible. Right. :-/ I=92ll just not make changes to the QAPI schema. It doesn=92t hurt to leav= e this in. Max > However, given that > the only known user of this interface is debug testing via iotests, I'm > not too concerned that we would be impacting any external users. --Ms7BYJ1fvZqURUh0mX06iL60AqIyyvjOt-- --TEypAhPXNjarWQ1iAPmjC13PFAKCCuEda Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl28Op4ACgkQ9AfbAGHV z0CkvggAqroXft5pdXXLNgeEU9ypp9x6fvVXvIkha68LyNIh7Jp0f7v4BCbTPGOQ keCFyq692E8/KRm7lOPaFCtPRZSFiudzWGY4BX+SCGsuzaR/swEA90USuaWtn/eG yaH6Z63ol8OvsOMmkan/YYoVw4z1JBUoYaAg93/rwokYVBEy2hbwxbGTdNTBgLAb IXdotLVCn47LIKpFUvIUf/9FyMqV9Z42U3LdrE0isgBcaMPXhG1TrF2vwqS6W7PQ FtD5UJTQDFCtV/CPa+bukIBIDKeQI9cKK51c5CRdFXj4nAFnuTJCVTSzYukE86hE 6ToqzlpzSXA7Lq2cndm4HLUuQJr9ug== =s3BU -----END PGP SIGNATURE----- --TEypAhPXNjarWQ1iAPmjC13PFAKCCuEda--