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

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

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.

-boris

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