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

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

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?

Josh

>> Implement this as bdrv_aio_flush, since it matches other aio functions
>> in the rbd block driver, and leave out bdrv_co_flush_to_disk when the
>> asynchronous version is available.
>>
>> Reported-by: Oliver Francke <oliver@filoo.de>
>> Signed-off-by: Josh Durgin <josh.durgin@inktank.com>
>
> Looks good otherwise.
>
> Kevin
>