Re: [Qemu-devel] [PATCH 0/4] qcow2: Improve cluster refcount update

[Laurent Vivier <Laurent.Vivier@bull.net>]

Le vendredi 07 novembre 2008 à 07:59 -0600, Anthony Liguori a écrit :
> Laurent Vivier wrote:
> > BTW, patch #1 is a clean-up (no change, only code move) and patch #2
> > doesn't align buffer, but try to minimise syscall (it improves
> > performance with O_DSYNC too).
> >
> > Ignore patch #3 and #4 if you dislike them.
> >   
> 
> But how useful is #1 and #2 if the buffers aren't aligned and we're 
> hitting the slow path?

In all cases #1 is totally useless as it is only cosmetic.

#2 improves performance without aligned buffers and with "cache" set to
default value.

I've installed ubuntu 8.04 desktop on an empty qcow2 file using qemu:

without patch: 16 minutes 54 seconds
with    patch: 15 minutes 44 seconds

Regards,
Laurent
-- 
------------------ Laurent.Vivier@bull.net  ------------------
"Tout ce qui est impossible reste à accomplir"    Jules Verne
"Things are only impossible until they're not" Jean-Luc Picard