[Intel-gfx] [RFC] drm/i915/bdw+: Do not emit user interrupts when not needed

[Chris Wilson]

On Fri, Dec 18, 2015 at 11:59:41AM +0000, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> We can rely on context complete interrupt to wake up the waiters
> apart in the case where requests are merged into a single ELSP
> submission. In this case we inject MI_USER_INTERRUPTS in the
> ring buffer to ensure prompt wake-ups.
> 
> This optimization has the effect on for example GLBenchmark
> Egypt off-screen test of decreasing the number of generated
> interrupts per second by a factor of two, and context switched
> by factor of five to six.

Another question is how many of those are distinct master interrupts? If
the latency between the user interrupt + context switch interrupt is
small enough not to be noticeable, then it should be small enough to be
in the same IIR (or next in the double buffered IIR)? Why is that
reasoning off?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre