[Intel-gfx] [Intel-gfx 1/1] drm/i915/guc: Don't update engine busyness stats too frequently

[Alan Previn]

Using igt's gem-create and with additional patches to track object
creation time, it was measured that guc_update_engine_gt_clks was
getting called over 188 thousand times in the span of 15 seconds
(running the test three times).

Get a jiffies sample on every trigger and ensure we skip sampling
if we are being called too soon. Use half of the ping_delay as a
safe threshold.

NOTE: with this change, the number of calls went down to just 14
over the same span of time (matching the original intent of running
about once every 24 seconds, at 19.2Mhz GT freq, per engine).

Signed-off-by: Alan Previn <alan.previn.teres.alexis at intel.com>
---
 drivers/gpu/drm/i915/gt/intel_engine_types.h      | 10 ++++++++++
 drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c |  9 +++++++++
 2 files changed, 19 insertions(+)

diff --git a/drivers/gpu/drm/i915/gt/intel_engine_types.h b/drivers/gpu/drm/i915/gt/intel_engine_types.h
index 2286f96f5f87..63f4ecdf1606 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_types.h
+++ b/drivers/gpu/drm/i915/gt/intel_engine_types.h
@@ -323,6 +323,16 @@ struct intel_engine_guc_stats {
 	 * @start_gt_clk: GT clock time of last idle to active transition.
 	 */
 	u64 start_gt_clk;
+
+	/**
+	 * @last_jiffies: Jiffies at last actual stats collection time
+	 *
+	 * We use this timestamp to ensure we don't oversample the
+	 * stats because runtime power management events can trigger
+	 * stats collection at much higher rates than required.
+	 */
+	u64 last_jiffies;
+
 };
 
 struct intel_engine_cs {
diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
index 5a1dfacf24ea..8f8bf6e40ccb 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
@@ -1167,6 +1167,15 @@ static void guc_update_engine_gt_clks(struct intel_engine_cs *engine)
 	struct intel_engine_guc_stats *stats = &engine->stats.guc;
 	struct intel_guc *guc = &engine->gt->uc.guc;
 	u32 last_switch, ctx_id, total;
+	u64 newjiffs;
+
+	/* Don't worry about jiffies wrap-around, a rare additional sample won't have any impact */
+	newjiffs = get_jiffies_64();
+	if (stats->last_jiffies && (newjiffs - stats->last_jiffies <
+	   (guc->timestamp.ping_delay << 1)))
+		return;
+
+	stats->last_jiffies = newjiffs;
 
 	lockdep_assert_held(&guc->timestamp.lock);
 
-- 
2.25.1