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

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

Hi, Jan/Konrad
   Do you have further comments about this patch ?   Thanks!
Xiantao

> -----Original Message-----
> From: Hao, Xudong
> Sent: Wednesday, May 09, 2012 2:26 PM
> To: Jan Beulich; Konrad Rzeszutek Wilk
> Cc: xen-devel; Zhang, Xiantao
> Subject: RE: [Xen-devel] [PATCH v2] Re-enable LTR/OBFF when device is
> owned by pciback
> 
> > -----Original Message-----
> > From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> > Sent: Tuesday, May 08, 2012 5:42 PM
> > To: Hao, Xudong; Konrad Rzeszutek Wilk
> > Cc: xen-devel
> > Subject: Re: [Xen-devel] [PATCH v2] Re-enable LTR/OBFF when device is
> > owned by pciback
> >
> > >>> On 08.05.12 at 11:05, "Hao, Xudong" <xudong.hao@xxxxxxxxx> wrote:
> > >>  -----Original Message-----
> > >> From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@xxxxxxxxxx] On Sun,
> > >> May 06, 2012 at 07:35:47AM +0000, Hao, Xudong wrote:
> > >> > > From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@xxxxxxxxxx]
> > >> > > Don't you need to disable this when the device is un-assigned
> > >> > > from the
> > >> guest?
> > >> > >
> > >> >
> > >> > I don't think this need to be disabled when device is un-assigned
> > >> > from
> > > guest.
> > >> If host want to use device again, the host device driver need
> > >> re-load, so whether disabling ltr/obff is up to host device driver.
> > >>
> > >> What if the driver isn't doing that?
> > >
> > > Make it clear, here host side do not be considered, host has its own
> driver.
> > > The only thing is to make sure ltr/obff is enabled before assigning
> > > guest, so that benefit on power.
> > >
> > > Since device is owned by pciback again when it un-assigned from
> > > guest, we need not disable explicitly.
> >
> > As you didn't answer my respective earlier question - _if_ this is a
> > feature needing enabling (and parameter tweaking), I'd imply there are
> > possible incompatibilities (i.e. reasons for not enabling this
> > always), and hence this shouldn't be done universally (and with fixed
> > values for the parameters) _and_ should be properly reset.
> >
> Only Xen administrator can hide a device by pciback, and can assign a device
> to guest. These power feature such as ltr and obff should be enabled by a
> sys-admin, I do not know which situation is a possible disabling these
> features, and why sys-admin want to disable them?

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