[Intel-gfx] [PATCH v2] drm/i915/perf: rate limit spurious oa report notice

[Robert Bragg]

This change is pre-emptively aiming to avoid a potential cause of kernel
logging noise in case some condition were to result in us seeing invalid
OA reports.

The workaround for the OA unit's tail pointer race condition is what
avoids the primary know cause of invalid reports being seen and with
that in place we aren't expecting to see this notice but it can't be
entirely ruled out.

Just in case some condition does lead to the notice then it's likely
that it will be triggered repeatedly while attempting to append a
sequence of reports and depending on the configured OA sampling
frequency that might be a large number of repeat notices.

v2: (Chris) avoid inconsistent warning on throttle with
    printk_ratelimit()

Signed-off-by: Robert Bragg <robert at sixbynine.org>
---
 drivers/gpu/drm/i915/i915_drv.h  |  6 ++++++
 drivers/gpu/drm/i915/i915_perf.c | 17 ++++++++++++++++-
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index a7b49cad6ab2..a7986c0c29ad 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2471,6 +2471,12 @@ struct drm_i915_private {
 			wait_queue_head_t poll_wq;
 			bool pollin;
 
+			/**
+			 * For rate limiting any notifications of spurious
+			 * invalid OA reports
+			 */
+			struct ratelimit_state spurious_report_rs;
+
 			bool periodic;
 			int period_exponent;
 
diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
index c09a7c9b61d9..36d07ca68029 100644
--- a/drivers/gpu/drm/i915/i915_perf.c
+++ b/drivers/gpu/drm/i915/i915_perf.c
@@ -632,7 +632,8 @@ static int gen7_append_oa_reports(struct i915_perf_stream *stream,
 		 * copying it to userspace...
 		 */
 		if (report32[0] == 0) {
-			DRM_NOTE("Skipping spurious, invalid OA report\n");
+			if (__ratelimit(&dev_priv->perf.oa.spurious_report_rs))
+				DRM_NOTE("Skipping spurious, invalid OA report\n");
 			continue;
 		}
 
@@ -2144,6 +2145,15 @@ void i915_perf_init(struct drm_i915_private *dev_priv)
 	if (!IS_HASWELL(dev_priv))
 		return;
 
+	/* Using the same limiting factors as printk_ratelimit() */
+	ratelimit_state_init(&dev_priv->perf.oa.spurious_report_rs,
+			5 * HZ, 10);
+	/* We use a DRM_NOTE for spurious reports so it would be
+	 * inconsistent to print a warning for throttling.
+	 */
+	ratelimit_set_flags(&dev_priv->perf.oa.spurious_report_rs,
+			RATELIMIT_MSG_ON_RELEASE);
+
 	hrtimer_init(&dev_priv->perf.oa.poll_check_timer,
 		     CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 	dev_priv->perf.oa.poll_check_timer.function = oa_poll_check_timer_cb;
@@ -2182,6 +2192,11 @@ void i915_perf_fini(struct drm_i915_private *dev_priv)
 	if (!dev_priv->perf.initialized)
 		return;
 
+	if (dev_priv->perf.oa.spurious_report_rs.missed) {
+		DRM_NOTE("%d spurious OA report notices suppressed due to ratelimiting",
+			 dev_priv->perf.oa.spurious_report_rs.missed);
+	}
+
 	unregister_sysctl_table(dev_priv->perf.sysctl_header);
 
 	memset(&dev_priv->perf.oa.ops, 0, sizeof(dev_priv->perf.oa.ops));
-- 
2.12.0