From: Max Reitz <mreitz@redhat.com>
To: Kevin Wolf <kwolf@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 17:02:19 +0100 [thread overview]
Message-ID: <d6864a28-ed91-29d4-e4cc-dacc26f1b764@redhat.com> (raw)
In-Reply-To: <20191101154241.GA23153@localhost.localdomain>
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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 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?
This isn’t output at all, it’s input for blockdev-add for blkdebug nodes.
Max
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next prev parent reply other threads:[~2019-11-01 16:08 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
2019-11-01 16:02 ` Max Reitz [this message]
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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