From: Eric Blake <eblake@redhat.com>
To: John Snow <jsnow@redhat.com>,
qemu-block@nongnu.org, qemu-devel@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>,
pbonzini@redhat.com, vsementsov@virtuozzo.com,
Markus Armbruster <armbru@redhat.com>,
Max Reitz <mreitz@redhat.com>
Subject: Re: [Qemu-devel] [PATCH v2] blockdev: acquire aio_context for bitmap add/remove
Date: Tue, 12 Feb 2019 16:04:31 -0600 [thread overview]
Message-ID: <445f2f21-d769-14f5-2259-80b3ea6e9988@redhat.com> (raw)
In-Reply-To: <87241634-5a14-f943-8446-07bd34f12aff@redhat.com>
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On 2/12/19 3:37 PM, John Snow wrote:
>
>
> On 2/12/19 3:16 PM, Eric Blake wrote:
>> On 2/12/19 2:07 PM, John Snow wrote:
>>> When bitmaps are persistent, they may incur a disk read or write when bitmaps
>>> are added or removed. For configurations like virtio-dataplane, failing to
>>> acquire this lock will abort QEMU when disk IO occurs.
>>>
>>> We used to acquire aio_context as part of the bitmap lookup, so re-introduce
>>> the lock for just the cases that have an IO penalty.
>>
>> It would be nice to call out which commit id dropped the aio_context
>> acquisition during bitmap lookup (making it easier to analyze how long
>> this has broken, and which downstream builds need the backport.
>>
>
> OK, I will amend this.
>
> Looks like:
>
> commit 2119882c7eb7e2c612b24fc0c8d86f5887d6f1c3
> Author: Paolo Bonzini <pbonzini@redhat.com>
> Date: Mon Jun 5 14:39:03 2017 +0200
>
> since 2.10.
Hmm. block-dirty-bitmap-add's "persistent":true parameter was also added
in 2.10 in commit fd5ae4cc. In fact, 2119882c was made at a time when
there were not persistent bitmaps; so I guess that this means we have
always been broken since fd5ae4cc.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
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next prev parent reply other threads:[~2019-02-12 22:05 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-12 20:07 [Qemu-devel] [PATCH v2] blockdev: acquire aio_context for bitmap add/remove John Snow
2019-02-12 20:16 ` Eric Blake
2019-02-12 21:37 ` John Snow
2019-02-12 22:04 ` Eric Blake [this message]
2019-02-13 16:41 ` no-reply
2019-02-14 4:26 ` no-reply
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