Re: [Xen-devel] question: xen/qemu - mmio mapping issues for device pass-through

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.03.17 at 14:55, <xuquan8@xxxxxxxxxx> wrote:
> I try to pass-through a device with 8G large bar, such as nvidia M60(note1, 
> pci-e info as below). It takes about '__15 sconds__' to update 8G large bar 
> in 
> QEMU::xen_pt_region_update()..
> Specifically, it is xc_domain_memory_mapping() in xen_pt_region_update().
> 
> Digged into xc_domain_memory_mapping(), I find it mainly call "do_domctl 
> （…case XEN_DOMCTL_memory_mapping…）" 
> to mapping mmio region.. of cause, I find out that this mapping could take a 
> while in the code comment below ' case XEN_DOMCTL_memory_mapping '.
> 
> my questions:
> 1. could we make this mapping mmio region quicker?

Yes, e.g. by using large (2M or 1G) pages. This has been on my todo
list for quite a while...

> 2. if could not, does it limit by hardware performance?

I'm afraid I don't understand the question. If you mean "Is it
limited by hw performance", then no, see above. If you mean
"Does it limit hw performance", then again no, I don't think so
(other than the effect of having more IOMMU translation levels
than really necessary for such large a region).

Jan

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