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Fri, 1 Nov 2019 16:02:26 +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 C1EF15C297; Fri, 1 Nov 2019 16:02:20 +0000 (UTC) Subject: Re: [PATCH for-4.2 1/4] Revert "qcow2: skip writing zero buffers to empty COW areas" To: Kevin Wolf References: <20191101100019.9512-1-mreitz@redhat.com> <20191101100019.9512-2-mreitz@redhat.com> <20191101154241.GA23153@localhost.localdomain> 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 17:02:19 +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: <20191101154241.GA23153@localhost.localdomain> 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="rc09sqFmyXbTOfWoFyNuUnKtMuAzhyDjC" 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: Vladimir Sementsov-Ogievskiy , qemu-block@nongnu.org, qemu-devel@nongnu.org, Anton Nefedov , 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) --rc09sqFmyXbTOfWoFyNuUnKtMuAzhyDjC Content-Type: multipart/mixed; boundary="GN5U5G54LsBYoMt53GWKFEiMZhS4xQ6bf" --GN5U5G54LsBYoMt53GWKFEiMZhS4xQ6bf Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 01.11.19 16:42, Kevin Wolf wrote: > Am 01.11.2019 um 15:01 hat Max Reitz geschrieben: >> 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 originall= y >>>> 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 >>>> --- >>> >>>> +++ b/qapi/block-core.json >>>> @@ -3304,8 +3304,6 @@ >>>> =C2=A0 # >>>> =C2=A0 # @cor_write: a write due to copy-on-read (since 2.11) >>>> =C2=A0 # >>>> -# @cluster_alloc_space: an allocation of file space for a cluster >>>> (since 4.1) >>>> -# >>>> =C2=A0 # @none: triggers once at creation of the blkdebug node (since = 4.1) >>> >>> Deleting released qapi is not backwards-compatible. >> >> Right. :-/ >> >> I=E2=80=99ll just not make changes to the QAPI schema. It doesn=E2=80= =99t hurt to leave >> this in. >=20 > Why would it be incompatible to drop an enum value that is only ever > used in output and that QEMU doesn't generate? This isn=E2=80=99t output at all, it=E2=80=99s input for blockdev-add for b= lkdebug nodes. 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