Re: [Xen-devel] [PATCH] ACPI: Add fixups for AMD P-state figures.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, Mar 06, 2013 at 10:48:01AM +0100, Stefan Bader wrote:
> On 05.03.2013 22:33, Konrad Rzeszutek Wilk wrote:
> > On Tue, Mar 05, 2013 at 03:22:25PM -0500, Boris Ostrovsky wrote:
> >> On 03/05/2013 02:45 PM, Konrad Rzeszutek Wilk wrote:
> >>> This a copy-n-paste from two Linux git commits:
> >>>
> >>> - f594065faf4f9067c2283a34619fc0714e79a98d
> >>>   ACPI: Add fixups for AMD P-state figures
> >>> - 9855d8ce41a7801548a05d844db2f46c3e810166
> >>>   ACPI: Check MSR valid bit before using P-state frequencies
> >>>
> >>> The issue is that "some AMD systems may round the frequencies in
> >>> ACPI tables to 100MHz boundaries. We canobtain the real
> >>> frequencies from MSRs, so add a quirk to fix these frequencies up
> >>> on AMD systems." (from f594065..)
> >>>
> >>> In discussion (around 9855d8..) "it turned out that indeed real
> >>> HW/BIOSes may choose to not set the valid bit and thus mark the
> >>> P-state as invalid. So this could be considered a fix for broken
> >>> BIOSes that also works around the issue on Xen." (from 9855d8..)
> >>>
> >>> I've tested it under Dell Inc. PowerEdge T105 /0RR825, BIOS 1.3.2
> >>> 08/20/2008 where this quirk can indeed be observed.
> >>>
> >>> CC: stefan.bader@xxxxxxxxxxxxx
> >>> CC: bp@xxxxxxx
> >>> CC: borislav.ostrovsky@xxxxxxxxxx
> >>
> >> boris.ostrovsky@xxxxxxxxxx
> > 
> > Whoops!
> > 
> > Here is an updated version:
> > 
> > From 3b7584f0c3c91d073bd760a038d0091b3bf5a19b Mon Sep 17 00:00:00 2001
> > From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> > Date: Tue, 5 Mar 2013 14:40:52 -0500
> > Subject: [PATCH] ACPI: Add fixups for AMD P-state figures.
> > 
> > This a copy-n-paste from two Linux git commits:
> > 
> > - f594065faf4f9067c2283a34619fc0714e79a98d
> >   ACPI: Add fixups for AMD P-state figures
> > - 9855d8ce41a7801548a05d844db2f46c3e810166
> >   ACPI: Check MSR valid bit before using P-state frequencies
> > 
> > The issue is that "some AMD systems may round the frequencies in
> > ACPI tables to 100MHz boundaries. We canobtain the real
> > frequencies from MSRs, so add a quirk to fix these frequencies up
> > on AMD systems." (from f594065..)
> > 
> > In discussion (around 9855d8..) "it turned out that indeed real
> > HW/BIOSes may choose to not set the valid bit and thus mark the
> > P-state as invalid. So this could be considered a fix for broken
> > BIOSes that also works around the issue on Xen." (from 9855d8..)
> 
> Boris and Jan already pointed out more than I would have spotted. So it seems
> the only thing left is the commit description. Well maybe it is just my way of
> reading it but it feels like here the actual description/argument is missing.
> 
> I think it might be that Xen gets the unmodified values from the ACPI parsing 
> in
> dom0 because it cannot/does not want to allow dom0 to read the MSR.

Right.
> Instead this patch will cause the frequencies to be adapted in the hypervisor.

Correct.

I will update the git commit with such wording and send out an updated
patch shortly.

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