Re: [PATCH 14/20] drm/i915/gt: Track timeline activeness in enter/exit

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On 18/07/2019 08:00, Chris Wilson wrote:
Lift moving the timeline to/from the active_list on enter/exit in order
to shorten the active tracking span in comparison to the existing
pin/unpin.

Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
---
  drivers/gpu/drm/i915/gem/i915_gem_pm.c        |  1 -
  drivers/gpu/drm/i915/gt/intel_context.c       |  2 +
  drivers/gpu/drm/i915/gt/intel_engine_pm.c     |  1 +
  drivers/gpu/drm/i915/gt/intel_lrc.c           |  4 +
  drivers/gpu/drm/i915/gt/intel_timeline.c      | 98 +++++++------------
  drivers/gpu/drm/i915/gt/intel_timeline.h      |  3 +-
  .../gpu/drm/i915/gt/intel_timeline_types.h    |  1 +
  drivers/gpu/drm/i915/gt/selftest_timeline.c   |  2 -
  8 files changed, 46 insertions(+), 66 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_pm.c b/drivers/gpu/drm/i915/gem/i915_gem_pm.c
index 8faf262278ae..195ee6eedac0 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_pm.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_pm.c
@@ -39,7 +39,6 @@ static void i915_gem_park(struct drm_i915_private *i915)
  		i915_gem_batch_pool_fini(&engine->batch_pool);
  	}
- intel_timelines_park(i915);
  	i915_vma_parked(i915);
i915_globals_park();
diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
index 9830edda1ade..87c84cc0f658 100644
--- a/drivers/gpu/drm/i915/gt/intel_context.c
+++ b/drivers/gpu/drm/i915/gt/intel_context.c
@@ -242,10 +242,12 @@ int __init i915_global_context_init(void)
  void intel_context_enter_engine(struct intel_context *ce)
  {
  	intel_engine_pm_get(ce->engine);
+	intel_timeline_enter(ce->ring->timeline);
  }
void intel_context_exit_engine(struct intel_context *ce)
  {
+	intel_timeline_exit(ce->ring->timeline);
  	intel_engine_pm_put(ce->engine);
  }
diff --git a/drivers/gpu/drm/i915/gt/intel_engine_pm.c b/drivers/gpu/drm/i915/gt/intel_engine_pm.c
index e74fbf04a68d..072f65e6a09e 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_pm.c
+++ b/drivers/gpu/drm/i915/gt/intel_engine_pm.c
@@ -89,6 +89,7 @@ static bool switch_to_kernel_context(struct intel_engine_cs *engine)
/* Check again on the next retirement. */
  	engine->wakeref_serial = engine->serial + 1;
+	intel_timeline_enter(rq->timeline);
i915_request_add_barriers(rq);
  	__i915_request_commit(rq);
diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index 884dfc1cb033..aceb990ae3b9 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -3253,6 +3253,8 @@ static void virtual_context_enter(struct intel_context *ce)
for (n = 0; n < ve->num_siblings; n++)
  		intel_engine_pm_get(ve->siblings[n]);
+
+	intel_timeline_enter(ce->ring->timeline);

Here we couldn't enter all sibling contexts instead? Would be a bit wasteful I guess. And there must be a place where it is already done. But can't be on picking the engine, where is it?

  }
static void virtual_context_exit(struct intel_context *ce)
@@ -3260,6 +3262,8 @@ static void virtual_context_exit(struct intel_context *ce)
  	struct virtual_engine *ve = container_of(ce, typeof(*ve), context);
  	unsigned int n;
+ intel_timeline_exit(ce->ring->timeline);
+
  	for (n = 0; n < ve->num_siblings; n++)
  		intel_engine_pm_put(ve->siblings[n]);
  }
diff --git a/drivers/gpu/drm/i915/gt/intel_timeline.c b/drivers/gpu/drm/i915/gt/intel_timeline.c
index 6daa9eb59e19..4af0b9801d91 100644
--- a/drivers/gpu/drm/i915/gt/intel_timeline.c
+++ b/drivers/gpu/drm/i915/gt/intel_timeline.c
@@ -278,64 +278,11 @@ void intel_timelines_init(struct drm_i915_private *i915)
  	timelines_init(&i915->gt);
  }
-static void timeline_add_to_active(struct intel_timeline *tl)
-{
-	struct intel_gt_timelines *gt = &tl->gt->timelines;
-
-	mutex_lock(&gt->mutex);
-	list_add(&tl->link, &gt->active_list);
-	mutex_unlock(&gt->mutex);
-}
-
-static void timeline_remove_from_active(struct intel_timeline *tl)
-{
-	struct intel_gt_timelines *gt = &tl->gt->timelines;
-
-	mutex_lock(&gt->mutex);
-	list_del(&tl->link);
-	mutex_unlock(&gt->mutex);
-}
-
-static void timelines_park(struct intel_gt *gt)
-{
-	struct intel_gt_timelines *timelines = &gt->timelines;
-	struct intel_timeline *timeline;
-
-	mutex_lock(&timelines->mutex);
-	list_for_each_entry(timeline, &timelines->active_list, link) {
-		/*
-		 * All known fences are completed so we can scrap
-		 * the current sync point tracking and start afresh,
-		 * any attempt to wait upon a previous sync point
-		 * will be skipped as the fence was signaled.
-		 */
-		i915_syncmap_free(&timeline->sync);
-	}
-	mutex_unlock(&timelines->mutex);
-}
-
-/**
- * intel_timelines_park - called when the driver idles
- * @i915: the drm_i915_private device
- *
- * When the driver is completely idle, we know that all of our sync points
- * have been signaled and our tracking is then entirely redundant. Any request
- * to wait upon an older sync point will be completed instantly as we know
- * the fence is signaled and therefore we will not even look them up in the
- * sync point map.
- */
-void intel_timelines_park(struct drm_i915_private *i915)
-{
-	timelines_park(&i915->gt);
-}
-
  void intel_timeline_fini(struct intel_timeline *timeline)
  {
  	GEM_BUG_ON(timeline->pin_count);
  	GEM_BUG_ON(!list_empty(&timeline->requests));
- i915_syncmap_free(&timeline->sync);
-
  	if (timeline->hwsp_cacheline)
  		cacheline_free(timeline->hwsp_cacheline);
  	else
@@ -370,6 +317,7 @@ int intel_timeline_pin(struct intel_timeline *tl)
  	if (tl->pin_count++)
  		return 0;
  	GEM_BUG_ON(!tl->pin_count);
+	GEM_BUG_ON(tl->active_count);
err = i915_vma_pin(tl->hwsp_ggtt, 0, 0, PIN_GLOBAL | PIN_HIGH);
  	if (err)
@@ -380,7 +328,6 @@ int intel_timeline_pin(struct intel_timeline *tl)
  		offset_in_page(tl->hwsp_offset);
cacheline_acquire(tl->hwsp_cacheline);
-	timeline_add_to_active(tl);
return 0; @@ -389,6 +336,40 @@ int intel_timeline_pin(struct intel_timeline *tl)
  	return err;
  }
+void intel_timeline_enter(struct intel_timeline *tl)
+{
+	struct intel_gt_timelines *timelines = &tl->gt->timelines;
+
+	GEM_BUG_ON(!tl->pin_count);
+	if (tl->active_count++)
+		return;
+	GEM_BUG_ON(!tl->active_count); /* overflow? */
+
+	mutex_lock(&timelines->mutex);
+	list_add(&tl->link, &timelines->active_list);
+	mutex_unlock(&timelines->mutex);
+}
+
+void intel_timeline_exit(struct intel_timeline *tl)
+{
+	struct intel_gt_timelines *timelines = &tl->gt->timelines;
+
+	GEM_BUG_ON(!tl->active_count);
+	if (--tl->active_count)
+		return;
+
+	mutex_lock(&timelines->mutex);
+	list_del(&tl->link);
+	mutex_unlock(&timelines->mutex);

So we end up with one lock protecting tl->active_count and another for the list of active timelines?

+
+	/*
+	 * Since this timeline is idle, all bariers upon which we were waiting
+	 * must also be complete and so we can discard the last used barriers
+	 * without loss of information.
+	 */
+	i915_syncmap_free(&tl->sync);
+}
+
  static u32 timeline_advance(struct intel_timeline *tl)
  {
  	GEM_BUG_ON(!tl->pin_count);
@@ -546,16 +527,9 @@ void intel_timeline_unpin(struct intel_timeline *tl)
  	if (--tl->pin_count)
  		return;
- timeline_remove_from_active(tl);
+	GEM_BUG_ON(tl->active_count);
  	cacheline_release(tl->hwsp_cacheline);
- /*
-	 * Since this timeline is idle, all bariers upon which we were waiting
-	 * must also be complete and so we can discard the last used barriers
-	 * without loss of information.
-	 */
-	i915_syncmap_free(&tl->sync);
-
  	__i915_vma_unpin(tl->hwsp_ggtt);
  }
diff --git a/drivers/gpu/drm/i915/gt/intel_timeline.h b/drivers/gpu/drm/i915/gt/intel_timeline.h
index e08cebf64833..f583af1ba18d 100644
--- a/drivers/gpu/drm/i915/gt/intel_timeline.h
+++ b/drivers/gpu/drm/i915/gt/intel_timeline.h
@@ -77,9 +77,11 @@ static inline bool intel_timeline_sync_is_later(struct intel_timeline *tl,
  }
int intel_timeline_pin(struct intel_timeline *tl);
+void intel_timeline_enter(struct intel_timeline *tl);
  int intel_timeline_get_seqno(struct intel_timeline *tl,
  			     struct i915_request *rq,
  			     u32 *seqno);
+void intel_timeline_exit(struct intel_timeline *tl);
  void intel_timeline_unpin(struct intel_timeline *tl);
int intel_timeline_read_hwsp(struct i915_request *from,
@@ -87,7 +89,6 @@ int intel_timeline_read_hwsp(struct i915_request *from,
  			     u32 *hwsp_offset);
void intel_timelines_init(struct drm_i915_private *i915);
-void intel_timelines_park(struct drm_i915_private *i915);
  void intel_timelines_fini(struct drm_i915_private *i915);
#endif
diff --git a/drivers/gpu/drm/i915/gt/intel_timeline_types.h b/drivers/gpu/drm/i915/gt/intel_timeline_types.h
index 9a71aea7a338..b820ee76b7f5 100644
--- a/drivers/gpu/drm/i915/gt/intel_timeline_types.h
+++ b/drivers/gpu/drm/i915/gt/intel_timeline_types.h
@@ -58,6 +58,7 @@ struct intel_timeline {
  	 */
  	struct i915_syncmap *sync;
+ unsigned int active_count;

Is it becoming non-obvious what is pin_count and what is active_count? I suggest some comments dropped along the members here.

  	struct list_head link;
  	struct intel_gt *gt;
diff --git a/drivers/gpu/drm/i915/gt/selftest_timeline.c b/drivers/gpu/drm/i915/gt/selftest_timeline.c
index f0a840030382..d54113697745 100644
--- a/drivers/gpu/drm/i915/gt/selftest_timeline.c
+++ b/drivers/gpu/drm/i915/gt/selftest_timeline.c
@@ -816,8 +816,6 @@ static int live_hwsp_recycle(void *arg)
if (err)
  				goto out;
-
-			intel_timelines_park(i915); /* Encourage recycling! */
  		} while (!__igt_timeout(end_time, NULL));
  	}

Regards,

Tvrtko
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