Re: [Qemu-devel] Default cache mode

[Anthony Liguori]

On 06/29/2011 07:16 AM, Kevin Wolf wrote:
> Am 29.06.2011 14:06, schrieb Anthony Liguori:
> > On 06/29/2011 06:59 AM, Kevin Wolf wrote:
> > > Hi,
> > >
> > > I think we have touched this topic before during some IRC discussions or
> > > somewhere deep in a mailing list thread, but I think it hasn't been
> > > discussed on the list.
> > >
> > > Our default cache mode of cache=writethrough is extremely conservative
> > > and provides absolute safety at the cost of performance,
> >
> > But for the most part, we track bare metal fairly well in terms of block
> > performance, no?
> >
> > Or are you really referring to qcow2 as a specific example?  In the
> > past, we used a different default caching mode for qcow2.  I think that
> > could be done again if there was a compelling reason.
>
> No, people are also complaining about bad performance with raw. Which
> isn't really surprising when you do a flush after each single write
> request. O_SYNC is really much more than is needed in the average case.

Which file system on the host?

At any rate, I'm a big fan of making wce tunable in the guest and then I 
think setting wce=1 is quite reasonable to do by default.

Regards,

Anthony Liguori

> Kevin