Re: [Xen-devel] Re: [Qemu-devel] [PATCH] qemu and qemu-xen: support empty write barriers in xen_disk

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Christoph Hellwig writes ("Re: [Xen-devel] Re: [Qemu-devel] [PATCH] qemu and 
qemu-xen: support empty write barriers in xen_disk"):
> On Wed, Nov 24, 2010 at 10:18:40AM -0800, Jeremy Fitzhardinge wrote:
> > Linux wants is a useful thing to do and implement (especially since it
> > amounts to standardising the ?BSD extension).  I'm not sure of their
> > precise semantics (esp WRT ordering), but I think its already OK.
> 
> The nice bit is that a pure flush does not imply any odering at all.
> Which is how the current qemu driver implements the barrier requests
> anyway, so that needs some fixing.

Thanks for your comments.  Does that mean, though, that Stefano's
patch is actually making the situation worse, or simply that it isn't
making it as good as it should be ?

If it's an improvement it should be applied it even if it's not
perfect, and it sounds to me like we don't want to wait for the more
complicated discussion to finish and produce code ?

Ian.

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