[Qemu-devel] Re: [RFC][STABLE 0.13] Revert "qcow2: Use bdrv_(p)write_sync for metadata writes"

[Michael Tokarev <mjt@tls.msk.ru>]

24.08.2010 15:02, Stefan Hajnoczi wrote:
[]
> Sometimes an improvement has a side effect and it makes sense to hold
> back the improvement until the side effect can be resolved.  The
> period of time in which users could rely on qcow2 data integrity is
> small to none, I feel reverting the commit makes sense.

And I agree with this.

> QEMU 0.12.5 has qcow2 sync metadata writes in commit
> 37060c28e522843fbf6f7e59af745dfcb05b132c.  Was the performance
> regression spotted on 0.12.5 or 0.13?

It started as a debian bugreport ( http://bugs.debian.org/594069 )
which were reported once 0.12.5 entered debian testing.  So
it were spotted in 0.12.5, not 0.13.  I verfied the bug locally
and indeed, it makes _huge_ difference (0.12.4 vs 0.12.5), --
e.g 600mb mem windows7 hybernation on my machine now takes about
40 minutes to complete instead of ~20 sec in 0.12.4.

I'm reverting whole series (there are 5 patches in total, covering
qcow, qcow2, vmdk and vpc plus infrastructure) for debian 0.12
package.  It is sad but there's no other option for now.

/mjt