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    SubjectRe: [PATCH] drm/i915: By default, enable RC6 on IVB and SNB when reasonable
    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@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@ffwll.ch
    Mobile: +41 (0)79 365 57 48


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