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

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Tue, May 22, 2012 at 01:57:44AM +0000, Zhang, Xiantao wrote:
> Hi, Jan/Konrad
>    Do you have further comments about this patch ?   Thanks!

Well .. What about making this be in the generic code? That way
both KVM and Xen can benefit? And also then the default values
don't have to show up in two places.


> 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@suse.com]
> > > 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@intel.com> wrote:
> > > >>  -----Original Message-----
> > > >> From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@oracle.com] On Sun,
> > > >> May 06, 2012 at 07:35:47AM +0000, Hao, Xudong wrote:
> > > >> > > From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@oracle.com]
> > > >> > > 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?