Re: [Xen-devel] OVMF very slow on AMD

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On Thu, Jul 28, 2016 at 03:54:34PM -0400, Boris Ostrovsky wrote:
> On 07/28/2016 03:44 PM, Andrew Cooper wrote:
> >>>> As far as Intel vs AMD implementation in Xen, we have vmx_handle_cd()
> >>>> but no corresponding SVM code. Could it be that we need to set gPAT, for
> >>>> example?
> >>> A better approach would be to find out why ovmf insists on disabling
> >>> caches at all.  Even if we optimise the non-PCI-device case in the
> >>> hypervisor, a passthrough case will still run like treacle if caches are
> >>> disabled.
> >> True, we should understand why OVMF does this. But I think we also need
> >> to understand what makes Intel run faster. Or is it already clear from
> >> vmx_handle_cd()?
> > Wow this code is hard to follow :(
> >
> > handle_cd() is only called when an IOMMU is enabled and the domain in
> > question has access to real ioports or PCI devices.
> >
> > However, I really can't spot anything that ends up eliding the
> > cache-disable setting even for Intel.  This clearly needs further
> > investigation.
> 
> So as an easy start perhaps Anthony could check whether this call is
> made with his guest running on Intel.

No, handle_cd is never called on my guest.

-- 
Anthony PERARD

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