[Intel-gfx] [PATCH] drm/i915: By default, enable RC6 on IVB and SNB when reasonable

[Daniel Vetter]

On Wed, Nov 23, 2011 at 02:01:54PM +0000, David Woodhouse wrote:
> On Wed, 2011-11-23 at 11:26 +0100, Daniel Vetter wrote:
> > On Tue, Nov 22, 2011 at 07:31:34PM -0800, Keith Packard wrote:
> > > On Tue, 22 Nov 2011 20:15:31 +0000, Matthew Garrett <mjg at redhat.com> wrote:
> > > 
> > > > So the user has to choose between 5W of power saving or having dmar? And 
> > > > we default to giving them dmar? I think that's going to come as a 
> > > > surprise to people.
> > > 
> > > You'd have to go into the BIOS to turn this on for most machines at
> > > least?
> > > 
> > > But, yeah, it seems like we should be turning DMAR off unless explicitly
> > > requested; I can't understand how you'd ever need this running native on
> > > the hardware. Not exactly an area I care about deeply; I've always
> > > worked hard to make sure all virtualization garbage is disabled on every
> > > machine I use.
> > 
> > Problem is that we need to disable dmar on the entire box, afaics. And I
> > assume that a bunch of people abusing desktop boards as servers will call
> > "regression" on that.
> 
> Hm, do you really have to disable it for the entire box, or just the
> graphics?

At least for the dmar+gfx+semaphores hang I can reproduce, just disabling
dmar with intel_iommu=igfx_off is not good enough and iirc the same holds
for the dmar+rc6 hangs reported.

> Do we have a coherent erratum from Intel for the issues mentioned above
> with DMAR+gfx+RC6?

Afaik no errata applies to our dmar related troubles on snb. I've hoped
that ppgtt would magically fix this, and it seems to help quite a bit for
the semaphore hangs (but not everywhere). Couldn't yet look more into
this.
-Daniel
-- 
Daniel Vetter
Mail: daniel at ffwll.ch
Mobile: +41 (0)79 365 57 48