[PATCH 55/57] drm/i915/gt: Enable ring scheduling for gen5-7

[Chris Wilson]

Switch over from FIFO global submission to the priority-sorted
topographical scheduler. At the cost of more busy work on the CPU to
keep the GPU supplied with the next packet of requests, this allows us
to reorder requests around submission stalls and so allow low latency
under load while maintaining fairness between clients.

The downside is that we enable interrupts on all requests (unlike with
execlists where we have an interrupt for context switches). This means
that instead of receiving an interrupt for when we are waitng for
completion, we are processing them all the time, with noticeable
overhead of cpu time absorbed by the interrupt handler. The effect is
most pronounced on CPU-throughput limited renderers like uxa, where
performance can be degraded by 20% in the worst case. Nevertheless, this
is a pathological example of an obsolete userspace driver.

The expectation is that allowing request reordering will allow much
smoother UX that greatly compensates for reduced throughput under high
submission load (but low GPU load).

This also enables the timer based RPS for better powersaving, with the
exception of Valleyview whose PCU doesn't take kindly to our
interference.

References: 0f46832fab77 ("drm/i915: Mask USER interrupts on gen6 (until required)")
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c | 2 +-
 drivers/gpu/drm/i915/gt/intel_engine_cs.c             | 2 ++
 drivers/gpu/drm/i915/gt/intel_rps.c                   | 6 ++----
 3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c b/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c
index d3f87dc4eda3..2246b5c308dc 100644
--- a/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c
@@ -94,7 +94,7 @@ static int live_nop_switch(void *arg)
 			rq = i915_request_get(this);
 			i915_request_add(this);
 		}
-		if (i915_request_wait(rq, 0, HZ / 5) < 0) {
+		if (i915_request_wait(rq, 0, HZ) < 0) {
 			pr_err("Failed to populated %d contexts\n", nctx);
 			intel_gt_set_wedged(&i915->gt);
 			i915_request_put(rq);
diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
index c0b11f20dc70..a2d7d1aa303d 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
@@ -881,6 +881,8 @@ int intel_engines_init(struct intel_gt *gt)
 
 	if (HAS_EXECLISTS(gt->i915))
 		setup = intel_execlists_submission_setup;
+	else if (INTEL_GEN(gt->i915) >= 5)
+		setup = intel_ring_scheduler_setup;
 	else
 		setup = intel_ring_submission_setup;
 
diff --git a/drivers/gpu/drm/i915/gt/intel_rps.c b/drivers/gpu/drm/i915/gt/intel_rps.c
index a92769c62911..740ee3c95660 100644
--- a/drivers/gpu/drm/i915/gt/intel_rps.c
+++ b/drivers/gpu/drm/i915/gt/intel_rps.c
@@ -1082,9 +1082,7 @@ static bool gen6_rps_enable(struct intel_rps *rps)
 	intel_uncore_write_fw(uncore, GEN6_RP_DOWN_TIMEOUT, 50000);
 	intel_uncore_write_fw(uncore, GEN6_RP_IDLE_HYSTERSIS, 10);
 
-	rps->pm_events = (GEN6_PM_RP_UP_THRESHOLD |
-			  GEN6_PM_RP_DOWN_THRESHOLD |
-			  GEN6_PM_RP_DOWN_TIMEOUT);
+	rps->pm_events = GEN6_PM_RP_UP_THRESHOLD | GEN6_PM_RP_DOWN_THRESHOLD;
 
 	return rps_reset(rps);
 }
@@ -1392,7 +1390,7 @@ void intel_rps_enable(struct intel_rps *rps)
 	GEM_BUG_ON(rps->efficient_freq < rps->min_freq);
 	GEM_BUG_ON(rps->efficient_freq > rps->max_freq);
 
-	if (has_busy_stats(rps))
+	if (has_busy_stats(rps) && !IS_VALLEYVIEW(i915))
 		intel_rps_set_timer(rps);
 	else if (INTEL_GEN(i915) >= 6)
 		intel_rps_set_interrupts(rps);
-- 
2.20.1