[PATCH 10/28] drm/i915/execlists: Reduce lock contention between schedule/submit_request

Chris Wilson chris at chris-wilson.co.uk
Thu May 11 07:10:45 UTC 2017


If we do not require to perform priority bumping, and we haven't yet
submitted the request, we can update its priority in situ and skip
acquiring the engine locks -- thus avoiding any contention between us
and submit/execute.

v2: Remove the stack element from the list if we can do the early
assignment.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_lrc.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 7e41529bd074..3cfb4b145b75 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -767,6 +767,19 @@ static void execlists_schedule(struct drm_i915_gem_request *request, int prio)
 		list_safe_reset_next(dep, p, dfs_link);
 	}
 
+	/* If we didn't need to bump any existing priorities, and we haven't
+	 * yet submitted this request (i.e. there is no potential race with
+	 * execlists_submit_request()), we can set our own priority and skip
+	 * acquiring the engine locks.
+	 */
+	if (request->priotree.priority == INT_MIN) {
+		GEM_BUG_ON(!list_empty(&request->priotree.link));
+		request->priotree.priority = prio;
+		if (stack.dfs_link.next == stack.dfs_link.prev)
+			return;
+		__list_del_entry(&stack.dfs_link);
+	}
+
 	engine = request->engine;
 	spin_lock_irq(&engine->timeline->lock);
 
-- 
2.11.0



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