[PATCH 7/8] drm/i915/pmu: Wire up engine busy stats to PMU

Tvrtko Ursulin
2017-09-18T11:38:28Z

From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

We can use engine busy stats instead of the MMIO sampling timer
for better efficiency.

As minimum this saves period * num_engines / sec mmio reads,
and in a better case, when only engine busy samplers are active,
it enables us to not kick off the sampling timer at all.

v2: Rebase.
v3:
* Rebase, comments.
* Leave engine busyness controls out of workers.
v4: Checkpatch cleanup.
v5: Added comment to pmu_needs_timer change.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
---
drivers/gpu/drm/i915/i915_pmu.c | 40 ++++++++++++++++++++++++++++++---
drivers/gpu/drm/i915/intel_ringbuffer.h | 5 +++++
2 files changed, 42 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
index b7de6fe3cac7..ffba21eeb5d0 100644
--- a/drivers/gpu/drm/i915/i915_pmu.c
+++ b/drivers/gpu/drm/i915/i915_pmu.c
@@ -90,6 +90,11 @@ static unsigned int event_enabled_bit(struct perf_event *event)
return config_enabled_bit(event->attr.config);
}

+static bool supports_busy_stats(void)
+{
+ return i915.enable_execlists;
+}
+
static bool pmu_needs_timer(struct drm_i915_private *i915, bool gpu_active)
{
u64 enable;
@@ -115,6 +120,12 @@ static bool pmu_needs_timer(struct drm_i915_private *i915, bool gpu_active)
*/
if (!gpu_active)
enable &= ~ENGINE_SAMPLE_MASK;
+ /**
+ * Also there is software busyness tracking available we do not
+ * need the timer for I915_SAMPLE_BUSY counter.
+ */
+ else if (supports_busy_stats())
+ enable &= ~BIT(I915_SAMPLE_BUSY);

/**
* If some bits remain it means we need the sampling timer running.
@@ -192,7 +203,8 @@ static void engines_sample(struct drm_i915_private *dev_priv)
if (enable & BIT(I915_SAMPLE_QUEUED))
engine->pmu.sample[I915_SAMPLE_QUEUED] += PERIOD;

- if (enable & BIT(I915_SAMPLE_BUSY)) {
+ if ((enable & BIT(I915_SAMPLE_BUSY)) &&
+ !engine->pmu.busy_stats) {
u32 val;

fw = grab_forcewake(dev_priv, fw);
@@ -385,6 +397,9 @@ static u64 __i915_pmu_event_read(struct perf_event *event)

if (WARN_ON_ONCE(!engine)) {
/* Do nothing */
+ } else if (sample == I915_SAMPLE_BUSY &&
+ engine->pmu.busy_stats) {
+ val = ktime_to_ns(intel_engine_get_busy_time(engine));
} else {
val = engine->pmu.sample[sample];
}
@@ -438,6 +453,12 @@ static void i915_pmu_event_read(struct perf_event *event)
local64_add(new - prev, &event->count);
}

+static bool engine_needs_busy_stats(struct intel_engine_cs *engine)
+{
+ return supports_busy_stats() &&
+ (engine->pmu.enable & BIT(I915_SAMPLE_BUSY));
+}
+
static void i915_pmu_enable(struct perf_event *event)
{
struct drm_i915_private *i915 =
@@ -477,7 +498,14 @@ static void i915_pmu_enable(struct perf_event *event)

GEM_BUG_ON(sample >= I915_PMU_SAMPLE_BITS);
GEM_BUG_ON(engine->pmu.enable_count[sample] == ~0);
- engine->pmu.enable_count[sample]++;
+ if (engine->pmu.enable_count[sample]++ == 0) {
+ if (engine_needs_busy_stats(engine) &&
+ !engine->pmu.busy_stats) {
+ engine->pmu.busy_stats =
+ intel_enable_engine_stats(engine) == 0;
+ WARN_ON_ONCE(!engine->pmu.busy_stats);
+ }
+ }
}

/*
@@ -513,8 +541,14 @@ static void i915_pmu_disable(struct perf_event *event)
* Decrement the reference count and clear the enabled
* bitmask when the last listener on an event goes away.
*/
- if (--engine->pmu.enable_count[sample] == 0)
+ if (--engine->pmu.enable_count[sample] == 0) {
engine->pmu.enable &= ~BIT(sample);
+ if (!engine_needs_busy_stats(engine) &&
+ engine->pmu.busy_stats) {
+ engine->pmu.busy_stats = false;
+ intel_disable_engine_stats(engine);
+ }
+ }
}

GEM_BUG_ON(bit >= I915_PMU_MASK_BITS);
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index ae0a4c498a0f..cb58ce34ab13 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -265,6 +265,11 @@ struct intel_engine_cs {
* Our internal timer stores the current counter in this field.
*/
u64 sample[I915_ENGINE_SAMPLE_MAX];
+ /**
+ * @busy_stats: Has enablement of engine stats tracking been
+ * requested.
+ */
+ bool busy_stats;
} pmu;

/*
--
2.9.5