[Intel-gfx] [PATCH 7/9] drm/i915/gt: Switch to manual evaluation of RPS

[Chris Wilson <chris@chris-wilson.co.uk>]

As with the realisation for soft-rc6, we respond to idling the engines
within microseconds, far faster than the response times for HW RC6 and
RPS. Furthermore, our fast parking upon idle, prevents HW RPS from
running for many desktop workloads, as the RPS evaluation intervals are
on the order of tens of milliseconds, but the typical workload is just a
couple of milliseconds, but yet we still need to determine the best
frequency for user latency versus power.

Recognising that the HW evaluation intervals are a poor fit, and that
they were deprecated [in bspec at least] from gen10, start to wean
ourselves off them and replace the EI with a timer and our accurate
busy-stats. The principle benefit of manually evaluating RPS intervals
is that we can be more responsive for better performance and powersaving
for both spiky workloads and steady-state.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/1698
Fixes: 98479ada421a ("drm/i915/gt: Treat idling as a RPS downclock event")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Andi Shyti <andi.shyti@intel.com>
---
 drivers/gpu/drm/i915/gt/intel_engine_types.h |  5 ++
 drivers/gpu/drm/i915/gt/intel_rps.c          | 80 +++++++++++++++++++-
 drivers/gpu/drm/i915/gt/intel_rps.h          | 14 ++++
 drivers/gpu/drm/i915/gt/intel_rps_types.h    |  5 ++
 4 files changed, 103 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_engine_types.h b/drivers/gpu/drm/i915/gt/intel_engine_types.h
index d7250b2d4175..b2c3e8df3eba 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_types.h
+++ b/drivers/gpu/drm/i915/gt/intel_engine_types.h
@@ -551,6 +551,11 @@ struct intel_engine_cs {
 		 * Idle is defined as active == 0, active is active > 0.
 		 */
 		ktime_t start;
+
+		/**
+		 * @rps: Utilisation at last RPS sampling.
+		 */
+		ktime_t rps;
 	} stats;
 
 	struct {
diff --git a/drivers/gpu/drm/i915/gt/intel_rps.c b/drivers/gpu/drm/i915/gt/intel_rps.c
index 52151001d7ab..2e951e821ee8 100644
--- a/drivers/gpu/drm/i915/gt/intel_rps.c
+++ b/drivers/gpu/drm/i915/gt/intel_rps.c
@@ -45,6 +45,62 @@ static inline void set(struct intel_uncore *uncore, i915_reg_t reg, u32 val)
 	intel_uncore_write_fw(uncore, reg, val);
 }
 
+static void rps_timer(struct timer_list *t)
+{
+	struct intel_rps *rps = from_timer(rps, t, timer);
+	struct intel_engine_cs *engine;
+	enum intel_engine_id id;
+	ktime_t dt, last;
+	s64 max_busy = 0;
+
+	for_each_engine(engine, rps_to_gt(rps), id) {
+		dt = intel_engine_get_busy_time(engine);
+		last = engine->stats.rps;
+		engine->stats.rps = dt;
+
+		max_busy = max(max_busy, ktime_to_ns(ktime_sub(dt, last)));
+	}
+
+	dt = ktime_get();
+	last = rps->pm_timestamp;
+	rps->pm_timestamp = dt;
+
+	if (intel_rps_is_active(rps)) {
+		dt = ktime_sub(dt, last);
+
+		if (10 * max_busy > 9 * dt && /* >90% busy */
+		    rps->cur_freq < rps->max_freq_softlimit) {
+			rps->pm_iir |= GEN6_PM_RP_UP_THRESHOLD;
+			rps->pm_interval = 1;
+			schedule_work(&rps->work);
+		} else if (4 * max_busy < 3 * dt && /* <75% busy */
+			   rps->cur_freq > rps->min_freq_softlimit) {
+			rps->pm_iir |= GEN6_PM_RP_DOWN_THRESHOLD;
+			rps->pm_interval = 1;
+			schedule_work(&rps->work);
+		} else {
+			rps->last_adj = 0;
+		}
+
+		mod_timer(&rps->timer,
+			  jiffies + msecs_to_jiffies(rps->pm_interval));
+		rps->pm_interval = min(rps->pm_interval + 1, 15u);
+	}
+}
+
+static void rps_start_timer(struct intel_rps *rps)
+{
+	rps->pm_timestamp = ktime_sub(ktime_get(), rps->pm_timestamp);
+	rps->pm_interval = 1;
+	mod_timer(&rps->timer, jiffies + 1);
+}
+
+static void rps_stop_timer(struct intel_rps *rps)
+{
+	del_timer_sync(&rps->timer);
+	rps->pm_timestamp = ktime_sub(ktime_get(), rps->pm_timestamp);
+}
+
 static u32 rps_pm_mask(struct intel_rps *rps, u8 val)
 {
 	u32 mask = 0;
@@ -742,8 +798,11 @@ void intel_rps_unpark(struct intel_rps *rps)
 
 	mutex_unlock(&rps->lock);
 
+	rps->pm_iir = 0;
 	if (intel_rps_has_interrupts(rps))
 		rps_enable_interrupts(rps);
+	if (intel_rps_uses_timer(rps))
+		rps_start_timer(rps);
 
 	if (IS_GEN(rps_to_i915(rps), 5))
 		gen5_rps_update(rps);
@@ -754,6 +813,8 @@ void intel_rps_park(struct intel_rps *rps)
 	if (!intel_rps_clear_active(rps))
 		return;
 
+	if (intel_rps_uses_timer(rps))
+		rps_stop_timer(rps);
 	if (intel_rps_has_interrupts(rps))
 		rps_disable_interrupts(rps);
 
@@ -1211,6 +1272,19 @@ static unsigned long __ips_gfx_val(struct intel_ips *ips)
 	return ips->gfx_power + state2;
 }
 
+static bool has_busy_stats(struct intel_rps *rps)
+{
+	struct intel_engine_cs *engine;
+	enum intel_engine_id id;
+
+	for_each_engine(engine, rps_to_gt(rps), id) {
+		if (!intel_engine_supports_stats(engine))
+			return false;
+	}
+
+	return true;
+}
+
 void intel_rps_enable(struct intel_rps *rps)
 {
 	struct drm_i915_private *i915 = rps_to_i915(rps);
@@ -1255,7 +1329,9 @@ 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 (INTEL_GEN(i915) >= 6)
+	if (has_busy_stats(rps))
+		intel_rps_set_timer(rps);
+	else if (INTEL_GEN(i915) >= 6)
 		intel_rps_set_interrupts(rps);
 	else
 		/* Ironlake currently uses intel_ips.ko */ {}
@@ -1274,6 +1350,7 @@ void intel_rps_disable(struct intel_rps *rps)
 
 	intel_rps_clear_enabled(rps);
 	intel_rps_clear_interrupts(rps);
+	intel_rps_clear_timer(rps);
 
 	if (INTEL_GEN(i915) >= 6)
 		gen6_rps_disable(rps);
@@ -1689,6 +1766,7 @@ void intel_rps_init_early(struct intel_rps *rps)
 	mutex_init(&rps->power.mutex);
 
 	INIT_WORK(&rps->work, rps_work);
+	timer_setup(&rps->timer, rps_timer, 0);
 
 	atomic_set(&rps->num_waiters, 0);
 }
diff --git a/drivers/gpu/drm/i915/gt/intel_rps.h b/drivers/gpu/drm/i915/gt/intel_rps.h
index 0ce6a0e492ea..3e83b65eb3c6 100644
--- a/drivers/gpu/drm/i915/gt/intel_rps.h
+++ b/drivers/gpu/drm/i915/gt/intel_rps.h
@@ -80,5 +80,19 @@ static inline void intel_rps_clear_interrupts(struct intel_rps *rps)
 {
 	clear_bit(INTEL_RPS_INTERRUPTS, &rps->flags);
 }
+static inline bool intel_rps_uses_timer(const struct intel_rps *rps)
+{
+	return test_bit(INTEL_RPS_TIMER, &rps->flags);
+}
+
+static inline void intel_rps_set_timer(struct intel_rps *rps)
+{
+	set_bit(INTEL_RPS_TIMER, &rps->flags);
+}
+
+static inline void intel_rps_clear_timer(struct intel_rps *rps)
+{
+	clear_bit(INTEL_RPS_TIMER, &rps->flags);
+}
 
 #endif /* INTEL_RPS_H */
diff --git a/drivers/gpu/drm/i915/gt/intel_rps_types.h b/drivers/gpu/drm/i915/gt/intel_rps_types.h
index 624e93108da4..38083f0402d9 100644
--- a/drivers/gpu/drm/i915/gt/intel_rps_types.h
+++ b/drivers/gpu/drm/i915/gt/intel_rps_types.h
@@ -35,6 +35,7 @@ enum {
 	INTEL_RPS_ENABLED = 0,
 	INTEL_RPS_ACTIVE,
 	INTEL_RPS_INTERRUPTS,
+	INTEL_RPS_TIMER,
 };
 
 struct intel_rps {
@@ -44,8 +45,12 @@ struct intel_rps {
 	 * work, interrupts_enabled and pm_iir are protected by
 	 * dev_priv->irq_lock
 	 */
+	struct timer_list timer;
 	struct work_struct work;
 	unsigned long flags;
+
+	ktime_t pm_timestamp;
+	u32 pm_interval;
 	u32 pm_iir;
 
 	/* PM interrupt bits that should never be masked */
-- 
2.20.1

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