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

[Kevin Wolf <kwolf@redhat.com>]

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.

Kevin