[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH v2] blockdev: acquire aio_context for bitmap add
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCH v2] blockdev: acquire aio_context for bitmap add/remove |
Date: |
Tue, 12 Feb 2019 16:04:31 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 |
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 <address@hidden>
> 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
signature.asc
Description: OpenPGP digital signature