Re: [Qemu-devel] [RFC] Disk integrity in QEMU

[Laurent Vivier]

Le mardi 14 octobre 2008 à 17:21 +0200, Avi Kivity a écrit :
> Anthony Liguori wrote:
> > Avi Kivity wrote:
> >> Given that we don't have a zero-copy implementation yet, it is
> >> impossible to generate real performance data.
> >
> > Which means that it's premature to suggest switching the default to
> > O_DIRECT since it's not going to help right now.  It can be revisited
> > once we can do zero copy but again, I think it should be driven by
> > actual performance data.  My main point is that switching to O_DIRECT
> > right now is only going to hurt performance for some users, and most
> > likely help no one.
> 
> I am assuming that we will provide true O_DIRECT support soon.

If you remember, I tried to introduce zero copy when I wrote the
"cache=off" patch:

http://thread.gmane.org/gmane.comp.emulators.qemu/22148/focus=22149

but it was not correct (see Fabrice comment).

Laurent
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