[PATCH 17/60] drm/i915/gt: Convert stats.active to plain unsigned int
Chris Wilson
chris at chris-wilson.co.uk
Sun Jan 3 22:39:14 UTC 2021
As context-in/out is now always serialised, we do not have to worry
about concurrent enabling/disable of the busy-stats and can reduce the
atomic_t active to a plain unsigned int, and the seqlock to a seqcount.
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
drivers/gpu/drm/i915/gt/intel_engine_cs.c | 8 ++--
drivers/gpu/drm/i915/gt/intel_engine_stats.h | 45 ++++++++++++--------
drivers/gpu/drm/i915/gt/intel_engine_types.h | 4 +-
3 files changed, 34 insertions(+), 23 deletions(-)
diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
index 5ead72c1b7d2..d2a20e53b080 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
@@ -341,7 +341,7 @@ static int intel_engine_setup(struct intel_gt *gt, enum intel_engine_id id)
engine->schedule = NULL;
ewma__engine_latency_init(&engine->latency);
- seqlock_init(&engine->stats.lock);
+ seqcount_init(&engine->stats.lock);
ATOMIC_INIT_NOTIFIER_HEAD(&engine->context_status_notifier);
@@ -1735,7 +1735,7 @@ static ktime_t __intel_engine_get_busy_time(struct intel_engine_cs *engine,
* add it to the total.
*/
*now = ktime_get();
- if (atomic_read(&engine->stats.active))
+ if (READ_ONCE(engine->stats.active))
total = ktime_add(total, ktime_sub(*now, engine->stats.start));
return total;
@@ -1754,9 +1754,9 @@ ktime_t intel_engine_get_busy_time(struct intel_engine_cs *engine, ktime_t *now)
ktime_t total;
do {
- seq = read_seqbegin(&engine->stats.lock);
+ seq = read_seqcount_begin(&engine->stats.lock);
total = __intel_engine_get_busy_time(engine, now);
- } while (read_seqretry(&engine->stats.lock, seq));
+ } while (read_seqcount_retry(&engine->stats.lock, seq));
return total;
}
diff --git a/drivers/gpu/drm/i915/gt/intel_engine_stats.h b/drivers/gpu/drm/i915/gt/intel_engine_stats.h
index 58491eae3482..24fbdd94351a 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_stats.h
+++ b/drivers/gpu/drm/i915/gt/intel_engine_stats.h
@@ -17,33 +17,44 @@ static inline void intel_engine_context_in(struct intel_engine_cs *engine)
{
unsigned long flags;
- if (atomic_add_unless(&engine->stats.active, 1, 0))
+ if (engine->stats.active) {
+ engine->stats.active++;
return;
-
- write_seqlock_irqsave(&engine->stats.lock, flags);
- if (!atomic_add_unless(&engine->stats.active, 1, 0)) {
- engine->stats.start = ktime_get();
- atomic_inc(&engine->stats.active);
}
- write_sequnlock_irqrestore(&engine->stats.lock, flags);
+
+ /* The writer is serialised; but the pmu reader may be from hardirq */
+ local_irq_save(flags);
+ write_seqcount_begin(&engine->stats.lock);
+
+ engine->stats.start = ktime_get();
+ engine->stats.active++;
+
+ write_seqcount_end(&engine->stats.lock);
+ local_irq_restore(flags);
+
+ GEM_BUG_ON(!engine->stats.active);
}
static inline void intel_engine_context_out(struct intel_engine_cs *engine)
{
unsigned long flags;
- GEM_BUG_ON(!atomic_read(&engine->stats.active));
-
- if (atomic_add_unless(&engine->stats.active, -1, 1))
+ GEM_BUG_ON(!engine->stats.active);
+ if (engine->stats.active > 1) {
+ engine->stats.active--;
return;
-
- write_seqlock_irqsave(&engine->stats.lock, flags);
- if (atomic_dec_and_test(&engine->stats.active)) {
- engine->stats.total =
- ktime_add(engine->stats.total,
- ktime_sub(ktime_get(), engine->stats.start));
}
- write_sequnlock_irqrestore(&engine->stats.lock, flags);
+
+ local_irq_save(flags);
+ write_seqcount_begin(&engine->stats.lock);
+
+ engine->stats.active--;
+ engine->stats.total =
+ ktime_add(engine->stats.total,
+ ktime_sub(ktime_get(), engine->stats.start));
+
+ write_seqcount_end(&engine->stats.lock);
+ local_irq_restore(flags);
}
#endif /* __INTEL_ENGINE_STATS_H__ */
diff --git a/drivers/gpu/drm/i915/gt/intel_engine_types.h b/drivers/gpu/drm/i915/gt/intel_engine_types.h
index 75c9093b5e7f..d2346b425547 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_types.h
+++ b/drivers/gpu/drm/i915/gt/intel_engine_types.h
@@ -516,12 +516,12 @@ struct intel_engine_cs {
/**
* @active: Number of contexts currently scheduled in.
*/
- atomic_t active;
+ unsigned int active;
/**
* @lock: Lock protecting the below fields.
*/
- seqlock_t lock;
+ seqcount_t lock;
/**
* @total: Total time this engine was busy.
--
2.20.1
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