[Intel-gfx] [PATCH 1/2] drm/i915: re-enable semaphores by default

[Daniel Vetter]

On Wed, Nov 16, 2011 at 18:16, Keith Packard <keithp at keithp.com> wrote:
> On Wed, 16 Nov 2011 16:49:40 +0100, Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
>
>> So we need to check whether DMAR is enabled (on the
>> entire system, i.e. the variable exported for the ilk workaround is
>> not good enough)
>
> Can you figure out what *would* be sufficient? Getting semaphores turned
> on for the 99% who aren't enabling VT-d would be a fairly nice
> performance improvement.

Last time I've played around with all the combinations, only
intel_iommu=off was good enough to prevent the hang.
intel_iommu=igd_off still hangs (which is what the current value
exported by the dmar code dopends on, iirc). If I remember things
correctly, intel_iommu=off also reliably works around issues for all
reporters (both semaphores and rc6).

And for reproducing it, at least here the key ingredient seems to be a
kde4 desktop. Spare the jokes ;-)
-Daniel
-- 
Daniel Vetter
daniel.vetter at ffwll.ch - +41 (0) 79 365 57 48 - http://blog.ffwll.ch