Re: [Qemu-devel] [PATCH v2] rbd: add an asynchronous flush

[Josh Durgin <josh.durgin@inktank.com>]

On 04/11/2013 01:48 AM, Kevin Wolf wrote:
> Am 11.04.2013 um 10:02 hat Stefan Hajnoczi geschrieben:
>> On Wed, Apr 10, 2013 at 07:03:39AM -0700, Josh Durgin wrote:
>>> On 04/02/2013 07:10 AM, Kevin Wolf wrote:
>>>> Am 29.03.2013 um 21:03 hat Josh Durgin geschrieben:
>>>>> The existing bdrv_co_flush_to_disk implementation uses rbd_flush(),
>>>>> which is sychronous and causes the main qemu thread to block until it
>>>>> is complete. This results in unresponsiveness and extra latency for
>>>>> the guest.
>>>>>
>>>>> Fix this by using an asynchronous version of flush.  This was added to
>>>>> librbd with a special #define to indicate its presence, since it will
>>>>> be backported to stable versions. Thus, there is no need to check the
>>>>> version of librbd.
>>>>
>>>> librbd is linked dynamically and the version on the build host isn't
>>>> necessarily the same as the version qemu is run with. So shouldn't this
>>>> better be a runtime check?
>>>
>>> While we discuss runtime loading separately, would you mind taking this
>>> patch as-is for now?
>>
>> Hi Josh,
>> I'm happy with Patch v3 1/2.  Does that work for you?
>
> Only patch 1/2 would add dead code as .bdrv_aio_flush would never be
> called. I think we should rather take v1 of the series then, with the
> #ifdefs at build time.

Yes, that would be a problem with only v3 1/2. v2 of the original
series is fine, but v1 was accidentally missing a hunk. To be clear,
I think just http://patchwork.ozlabs.org/patch/232489/ would be good.

Thanks,
Josh