[Intel-gfx] [PATCH 25/42] drm/i915/gt: Convert stats.active to plain unsigned int

[Chris Wilson]

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 <ch...@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 b2f520bc1497..8de3105632ef 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
@@ -339,7 +339,7 @@ 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);
 
@@ -1714,7 +1714,7 @@ 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;
@@ -1733,9 +1733,9 @@ 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 2361206fd026..7ee9e32d149b 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_types.h
+++ b/drivers/gpu/drm/i915/gt/intel_engine_types.h
@@ -525,12 +525,12 @@ 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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