From: Kevin Wolf <kwolf@redhat.com>
To: Max Reitz <mreitz@redhat.com>
Cc: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>,
qemu-block@nongnu.org, qemu-devel@nongnu.org,
Anton Nefedov <anton.nefedov@virtuozzo.com>,
Stefan Hajnoczi <stefanha@redhat.com>
Subject: Re: [PATCH for-4.2 1/4] Revert "qcow2: skip writing zero buffers to empty COW areas"
Date: Fri, 1 Nov 2019 16:42:41 +0100 [thread overview]
Message-ID: <20191101154241.GA23153@localhost.localdomain> (raw)
In-Reply-To: <e8f8ae20-b036-4330-4851-f099fc534f9b@redhat.com>
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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 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 <mreitz@redhat.com>
> >> ---
> >
> >> +++ 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.
>
> Right. :-/
>
> I’ll just not make changes to the QAPI schema. It doesn’t hurt to leave
> this in.
Why would it be incompatible to drop an enum value that is only ever
used in output and that QEMU doesn't generate?
Kevin
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next prev parent reply other threads:[~2019-11-01 15:46 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-01 10:00 [PATCH for-4.2 0/4] qcow2: Fix data corruption on XFS Max Reitz
2019-11-01 10:00 ` [PATCH for-4.2 1/4] Revert "qcow2: skip writing zero buffers to empty COW areas" Max Reitz
2019-11-01 10:22 ` Vladimir Sementsov-Ogievskiy
2019-11-01 12:40 ` Eric Blake
2019-11-01 14:01 ` Max Reitz
2019-11-01 15:42 ` Kevin Wolf [this message]
2019-11-01 16:02 ` Max Reitz
2019-11-01 10:00 ` [PATCH for-4.2 2/4] block: Make wait/mark serialising requests public Max Reitz
2019-11-01 10:00 ` [PATCH for-4.2 3/4] block: Add bdrv_co_get_self_request() Max Reitz
2019-11-01 10:00 ` [PATCH for-4.2 4/4] block/file-posix: Let post-EOF fallocate serialize Max Reitz
2019-11-01 10:20 ` [PATCH for-4.2 0/4] qcow2: Fix data corruption on XFS Max Reitz
2019-11-01 10:28 ` Vladimir Sementsov-Ogievskiy
2019-11-01 11:12 ` Max Reitz
2019-11-01 11:16 ` Vladimir Sementsov-Ogievskiy
2019-11-01 11:20 ` Max Reitz
2019-11-01 12:34 ` Max Reitz
2019-11-01 13:09 ` Vladimir Sementsov-Ogievskiy
2019-11-01 13:36 ` Denis Lunev
2019-11-01 13:40 ` Max Reitz
2019-11-01 13:30 ` Max Reitz
2019-11-01 15:06 ` Max Reitz
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