Re: [Xen-devel] [PATCH v2] Re-enable LTR/OBFF when device is owned by pciback

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.05.12 at 16:45, "Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx> wrote:
> Okay,  I understand your concern about this implementation, and you think 
> ltr/obff should be enabled by guest instead of host.   AS we know, LTR/OBFF 
> is a special PCI-e feature for optimizing the whole system's  PM, and to 
> enable it, the whole system(including root port and all upstream bridges or 
> ports) should have these two capabilities. If anyone in this chain doesn't 
> have or enable  these two capabilities, the whole system would fail to 
> benefit from this optimized PM.   In addition, since Qemu doesn't have PCI-e 
> support, and also hasn't such  LTR/OBFF capabilities supported,  guest 
> shouldn't be able to enable this feature for its any device. 
> Certainly, we can change linux's pci interface and para-virtualize this two 
> features, in this way, guest can ask host to enable this feature, but how to 
> handle Windows guest's case ?  We can't change or para-virtualize Windows's 
> PCI interface, I think. Do you have good suggestion or proposals?  Thanks!

Fix qemu to support PCI-e (and then make use of the to be added
PV interface).

Jan


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