[Intel-gfx] [PATCH] drm/i915: Add I915_GEM_PARAM_HAS_SEMAPHORES

[Daniel Vetter]

On Wed, Aug 08, 2012 at 10:23:22AM +0100, Chris Wilson wrote:
> Userspace tries to estimate the cost of ring switching based on whether
> the GPU and GEM supports semaphores. (If we have multiple rings and no
> semaphores, userspace assumes that the cost of switching rings between
> batches is exorbitant and will endeavour to keep the next batch on the
> active ring - as a coarse approximation to tracking both destination and
> source surfaces.) Currently userspace has to guess whether semaphores
> exist based on the chipset generation and the module parameter,
> i915.semaphores. This is a crude and inaccurate guess as the defaults
> internally depend upon other chipset features being enabled or disabled,
> nor does it extend well into the future. By exporting a HAS_SEMAPHORES
> parameter, we can easily query the driver and obtain an accurate answer.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>

Sounds like something useful, applied for -next, thanks for the patch.
-Daniel
-- 
Daniel Vetter
Mail: daniel at ffwll.ch
Mobile: +41 (0)79 365 57 48