[Intel-gfx] [PATCH 8/8] drm/i915: Gate engine stats collection with a static key
Tvrtko Ursulin
tursulin at ursulin.net
Mon Sep 18 11:38:14 UTC 2017
From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
This reduces the cost of the software engine busyness tracking
to a single no-op instruction when there are no listeners.
v2: Rebase and some comments.
v3: Rebase.
v4: Checkpatch fixes.
v5: Rebase.
v6: Use system_long_wq to avoid being blocked by struct_mutex
users.
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
---
drivers/gpu/drm/i915/i915_pmu.c | 54 +++++++++++++++--
drivers/gpu/drm/i915/intel_engine_cs.c | 17 ++++++
drivers/gpu/drm/i915/intel_ringbuffer.h | 101 ++++++++++++++++++++------------
3 files changed, 130 insertions(+), 42 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
index ffba21eeb5d0..6d22172b8fb0 100644
--- a/drivers/gpu/drm/i915/i915_pmu.c
+++ b/drivers/gpu/drm/i915/i915_pmu.c
@@ -499,11 +499,17 @@ 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);
if (engine->pmu.enable_count[sample]++ == 0) {
+ /*
+ * Enable engine busy stats tracking if needed or
+ * alternatively cancel the scheduled disabling of the
+ * same.
+ */
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);
+ engine->pmu.busy_stats = true;
+ if (!cancel_delayed_work(&engine->pmu.disable_busy_stats))
+ queue_work(system_long_wq,
+ &engine->pmu.enable_busy_stats);
}
}
}
@@ -546,7 +552,15 @@ static void i915_pmu_disable(struct perf_event *event)
if (!engine_needs_busy_stats(engine) &&
engine->pmu.busy_stats) {
engine->pmu.busy_stats = false;
- intel_disable_engine_stats(engine);
+ /*
+ * We request a delayed disable to handle the
+ * rapid on/off cycles on events which can
+ * happen when tools like perf stat start in a
+ * nicer way.
+ */
+ queue_delayed_work(system_long_wq,
+ &engine->pmu.disable_busy_stats,
+ round_jiffies_up_relative(HZ));
}
}
}
@@ -737,9 +751,27 @@ static int i915_pmu_cpu_offline(unsigned int cpu, struct hlist_node *node)
return 0;
}
+static void __enable_busy_stats(struct work_struct *work)
+{
+ struct intel_engine_cs *engine =
+ container_of(work, typeof(*engine), pmu.enable_busy_stats);
+
+ WARN_ON_ONCE(intel_enable_engine_stats(engine));
+}
+
+static void __disable_busy_stats(struct work_struct *work)
+{
+ struct intel_engine_cs *engine =
+ container_of(work, typeof(*engine), pmu.disable_busy_stats.work);
+
+ intel_disable_engine_stats(engine);
+}
+
void i915_pmu_register(struct drm_i915_private *i915)
{
int ret;
+ struct intel_engine_cs *engine;
+ enum intel_engine_id id;
if (INTEL_GEN(i915) <= 2) {
DRM_INFO("PMU not supported for this GPU.");
@@ -773,6 +805,12 @@ void i915_pmu_register(struct drm_i915_private *i915)
i915->pmu.timer.function = i915_sample;
i915->pmu.enable = 0;
+ for_each_engine(engine, i915, id) {
+ INIT_WORK(&engine->pmu.enable_busy_stats, __enable_busy_stats);
+ INIT_DELAYED_WORK(&engine->pmu.disable_busy_stats,
+ __disable_busy_stats);
+ }
+
ret = perf_pmu_register(&i915->pmu.base, "i915", -1);
if (ret == 0)
return;
@@ -791,6 +829,9 @@ void i915_pmu_register(struct drm_i915_private *i915)
void i915_pmu_unregister(struct drm_i915_private *i915)
{
+ struct intel_engine_cs *engine;
+ enum intel_engine_id id;
+
if (!i915->pmu.base.event_init)
return;
@@ -802,6 +843,11 @@ void i915_pmu_unregister(struct drm_i915_private *i915)
hrtimer_cancel(&i915->pmu.timer);
+ for_each_engine(engine, i915, id) {
+ flush_work(&engine->pmu.enable_busy_stats);
+ flush_delayed_work(&engine->pmu.disable_busy_stats);
+ }
+
perf_pmu_unregister(&i915->pmu.base);
i915->pmu.base.event_init = NULL;
}
diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
index cbf978d39052..490b5254f2c0 100644
--- a/drivers/gpu/drm/i915/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/intel_engine_cs.c
@@ -21,6 +21,7 @@
* IN THE SOFTWARE.
*
*/
+#include <linux/static_key.h>
#include "i915_drv.h"
#include "intel_ringbuffer.h"
@@ -1558,6 +1559,10 @@ bool intel_engine_can_store_dword(struct intel_engine_cs *engine)
}
}
+DEFINE_STATIC_KEY_FALSE(i915_engine_stats_key);
+static DEFINE_MUTEX(i915_engine_stats_mutex);
+static int i915_engine_stats_ref;
+
/**
* intel_enable_engine_stats() - Enable engine busy tracking on engine
* @engine: engine to enable stats collection
@@ -1573,6 +1578,8 @@ int intel_enable_engine_stats(struct intel_engine_cs *engine)
if (!i915.enable_execlists)
return -ENODEV;
+ mutex_lock(&i915_engine_stats_mutex);
+
spin_lock_irqsave(&engine->stats.lock, flags);
if (engine->stats.enabled == ~0)
goto busy;
@@ -1580,10 +1587,16 @@ int intel_enable_engine_stats(struct intel_engine_cs *engine)
engine->stats.enabled_at = ktime_get();
spin_unlock_irqrestore(&engine->stats.lock, flags);
+ if (i915_engine_stats_ref++ == 0)
+ static_branch_enable(&i915_engine_stats_key);
+
+ mutex_unlock(&i915_engine_stats_mutex);
+
return 0;
busy:
spin_unlock_irqrestore(&engine->stats.lock, flags);
+ mutex_unlock(&i915_engine_stats_mutex);
return -EBUSY;
}
@@ -1601,6 +1614,7 @@ void intel_disable_engine_stats(struct intel_engine_cs *engine)
if (!i915.enable_execlists)
return;
+ mutex_lock(&i915_engine_stats_mutex);
spin_lock_irqsave(&engine->stats.lock, flags);
WARN_ON_ONCE(engine->stats.enabled == 0);
if (--engine->stats.enabled == 0) {
@@ -1610,6 +1624,9 @@ void intel_disable_engine_stats(struct intel_engine_cs *engine)
engine->stats.total = 0;
}
spin_unlock_irqrestore(&engine->stats.lock, flags);
+ if (--i915_engine_stats_ref == 0)
+ static_branch_disable(&i915_engine_stats_key);
+ mutex_unlock(&i915_engine_stats_mutex);
}
/**
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index cb58ce34ab13..2c3ddf862bde 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -270,6 +270,22 @@ struct intel_engine_cs {
* requested.
*/
bool busy_stats;
+ /**
+ * @enable_busy_stats: Work item for engine busy stats enabling.
+ *
+ * Since the action can sleep it needs to be decoupled from the
+ * perf API callback.
+ */
+ struct work_struct enable_busy_stats;
+ /**
+ * @disable_busy_stats: Work item for busy stats disabling.
+ *
+ * Same as with @enable_busy_stats action, with the difference
+ * that we delay it in case there are rapid enable-disable
+ * actions, which can happen during tool startup (like perf
+ * stat).
+ */
+ struct delayed_work disable_busy_stats;
} pmu;
/*
@@ -805,59 +821,68 @@ bool intel_engine_can_store_dword(struct intel_engine_cs *engine);
struct intel_engine_cs *
intel_engine_lookup_user(struct drm_i915_private *i915, u8 class, u8 instance);
+DECLARE_STATIC_KEY_FALSE(i915_engine_stats_key);
+
static inline void intel_engine_context_in(struct intel_engine_cs *engine)
{
unsigned long flags;
- if (READ_ONCE(engine->stats.enabled) == 0)
- return;
+ if (static_branch_unlikely(&i915_engine_stats_key)) {
+ if (READ_ONCE(engine->stats.enabled) == 0)
+ return;
- spin_lock_irqsave(&engine->stats.lock, flags);
+ spin_lock_irqsave(&engine->stats.lock, flags);
- if (engine->stats.enabled > 0) {
- if (engine->stats.active++ == 0)
- engine->stats.start = ktime_get();
- GEM_BUG_ON(engine->stats.active == 0);
- }
+ if (engine->stats.enabled > 0) {
+ if (engine->stats.active++ == 0)
+ engine->stats.start = ktime_get();
+ GEM_BUG_ON(engine->stats.active == 0);
+ }
- spin_unlock_irqrestore(&engine->stats.lock, flags);
+ spin_unlock_irqrestore(&engine->stats.lock, flags);
+ }
}
static inline void intel_engine_context_out(struct intel_engine_cs *engine)
{
unsigned long flags;
- if (READ_ONCE(engine->stats.enabled) == 0)
- return;
-
- spin_lock_irqsave(&engine->stats.lock, flags);
-
- if (engine->stats.enabled > 0) {
- ktime_t last, now = ktime_get();
-
- if (engine->stats.active && --engine->stats.active == 0) {
- /*
- * Decrement the active context count and in case GPU
- * is now idle add up to the running total.
- */
- last = ktime_sub(now, engine->stats.start);
-
- engine->stats.total = ktime_add(engine->stats.total,
- last);
- } else if (engine->stats.active == 0) {
- /*
- * After turning on engine stats, context out might be
- * the first event in which case we account from the
- * time stats gathering was turned on.
- */
- last = ktime_sub(now, engine->stats.enabled_at);
-
- engine->stats.total = ktime_add(engine->stats.total,
- last);
+ if (static_branch_unlikely(&i915_engine_stats_key)) {
+ if (READ_ONCE(engine->stats.enabled) == 0)
+ return;
+
+ spin_lock_irqsave(&engine->stats.lock, flags);
+
+ if (engine->stats.enabled > 0) {
+ ktime_t last, now = ktime_get();
+
+ if (engine->stats.active &&
+ --engine->stats.active == 0) {
+ /*
+ * Decrement the active context count and in
+ * case GPU is now idle add up to the running
+ * total.
+ */
+ last = ktime_sub(now, engine->stats.start);
+
+ engine->stats.total =
+ ktime_add(engine->stats.total, last);
+ } else if (engine->stats.active == 0) {
+ /*
+ * After turning on engine stats, context out
+ * might be the first event in which case we
+ * account from the time stats gathering was
+ * turned on.
+ */
+ last = ktime_sub(now, engine->stats.enabled_at);
+
+ engine->stats.total =
+ ktime_add(engine->stats.total, last);
+ }
+
+ spin_unlock_irqrestore(&engine->stats.lock, flags);
}
}
-
- spin_unlock_irqrestore(&engine->stats.lock, flags);
}
int intel_enable_engine_stats(struct intel_engine_cs *engine);
--
2.9.5
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