drm/i915/execlists: Set queue priority from secondary port
authorChris Wilson <chris@chris-wilson.co.uk>
Wed, 11 Apr 2018 10:39:29 +0000 (11:39 +0100)
committerChris Wilson <chris@chris-wilson.co.uk>
Wed, 11 Apr 2018 16:55:56 +0000 (17:55 +0100)
commit15c83c436424adf3fe0365e9085a82da1190c95e
treeb8dceb290b3afb8a1a5cedc7c6203b4466e37152
parentf3aa929c59c945e50386fde65d37c24e8a898e48
drm/i915/execlists: Set queue priority from secondary port

We can refine our current execlists->queue_priority if we inspect
ELSP[1] rather than the head of the unsubmitted queue. Currently, we use
the unsubmitted queue and say that if a subsequent request is more
important than the current queue, we will rerun the submission tasklet
to evaluate the need for preemption. However, we only want to preempt if
we need to jump ahead of a currently executing request in ELSP. The
second reason for running the submission tasklet is amalgamate requests
into the active context on ELSP[0] to avoid a stall when ELSP[0] drains.
(Though repeatedly amalgamating requests into the active context and
triggering many lite-restore is off question gain, the goal really is to
put a context into ELSP[1] to cover the interrupt.) So if instead of
looking at the head of the queue, we look at the context in ELSP[1] we
can answer both of the questions more accurately -- we don't need to
rerun the submission tasklet unless our new request is important enough
to feed into, at least, ELSP[1].

v2: Add some comments from the discussion with Tvrtko.
v3: More commentary to cross-reference queue_request()

References: f6322eddaff7 ("drm/i915/preemption: Allow preemption between submission ports")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: MichaƂ Winiarski <michal.winiarski@intel.com>
Cc: Michel Thierry <michel.thierry@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180411103929.27374-1-chris@chris-wilson.co.uk
drivers/gpu/drm/i915/intel_engine_cs.c
drivers/gpu/drm/i915/intel_lrc.c