Re: [Xen-devel] qemu-xen-traditional: NOCACHE or CACHE_WB to open disk images for IDE

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 14 Aug 2012, Ian Jackson wrote:
> Xu, Dongxiao writes ("RE: [Xen-devel] qemu-xen-traditional: NOCACHE or 
> CACHE_WB to open disk images for IDE"):
> > I attached the original patch here, which impact the performance.
> 
> Stefano, when you proposed what is now
> 1307e42a4b3c1102d75401bc0cffb4eb6c9b7a38 this you described it as a
> major performance improvement.
> 
> Would you care to comment ?

QDISK needs NOCACHE, that's why I wrote the original patch series.

I also thought that IDE also needs NOCACHE for safety but after a
lengthy discussion, we came up with the conclusion that WRITEBACK is
OK for IDE, see your message:

http://marc.info/?l=xen-devel&m=133311527009773

So I think we should revert 1307e42a4b3c1102d75401bc0cffb4eb6c9b7a38, I
don't know why it was committed.

Also it seems to me that libxl is not specifying cache=writeback for
upstream QEMU, that means it is going to default to writethrough.
I'll write a patch for that.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel