[Intel-gfx] [PATCH 40/41] drm/i915/gt: Enable ring scheduling for gen5-7

Chris Wilson chris at chris-wilson.co.uk
Mon Jan 25 14:01:35 UTC 2021

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. (There are
also cases where uxa performs better by 20%, which is an interesting
quirk...) The glxgears-not-a-benchmark (cpu throughtput bound) is one
such example of a performance hit, only affecting uxa.

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

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);
-		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);
diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
index 936820b240dd..99d910f2c172 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
@@ -868,6 +868,8 @@ int intel_engines_init(struct intel_gt *gt)
 		setup = intel_guc_submission_setup;
 	else if (HAS_EXECLISTS(gt->i915))
 		setup = intel_execlists_submission_setup;
+	else if (INTEL_GEN(gt->i915) >= 5)
+		setup = intel_ring_scheduler_setup;
 		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 900c20a6d073..2c78d61e7ea9 100644
--- a/drivers/gpu/drm/i915/gt/intel_rps.c
+++ b/drivers/gpu/drm/i915/gt/intel_rps.c
@@ -1081,9 +1081,7 @@ 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 |
 	return rps_reset(rps);
@@ -1391,7 +1389,7 @@ 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))
 	else if (INTEL_GEN(i915) >= 6)

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