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

["Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx>]

Hi, Jan 
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!
Xiantao




> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Tuesday, May 22, 2012 3:21 PM
> To: Zhang, Xiantao; Hao, Xudong
> Cc: xen-devel; Konrad Rzeszutek Wilk
> Subject: RE: [Xen-devel] [PATCH v2] Re-enable LTR/OBFF when device is
> owned by pciback
> 
> >>> On 22.05.12 at 03:57, "Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx>
> wrote:
> >    Do you have further comments about this patch ?   Thanks!
> 
> I don't have anything beyond the reservations I have already expressed (and
> which remain in place).
> 
> Jan


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