drm/i915/perf: rate limit spurious oa report notice

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 known 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()
v3: (Matt) init and summarise with stream init/close not driver init/fini

Signed-off-by: Robert Bragg <robert@sixbynine.org>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170511154345.962-9-lionel.g.landwerlin@intel.com
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_drv.h

@@ -2354,6 +2354,12 @@ 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;
 

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;
 		}
 
@@ -911,6 +912,11 @@ static void i915_oa_stream_destroy(struct i915_perf_stream *stream)
 		oa_put_render_ctx_id(stream);
 
 	dev_priv->perf.oa.exclusive_stream = NULL;
+
+	if (dev_priv->perf.oa.spurious_report_rs.missed) {
+		DRM_NOTE("%d spurious OA report notices suppressed due to ratelimiting\n",
+			 dev_priv->perf.oa.spurious_report_rs.missed);
+	}
 }
 
 static void gen7_init_oa_buffer(struct drm_i915_private *dev_priv)
@@ -1266,6 +1272,26 @@ static int i915_oa_stream_init(struct i915_perf_stream *stream,
 		return -EINVAL;
 	}
 
+	/* We set up some ratelimit state to potentially throttle any _NOTES
+	 * about spurious, invalid OA reports which we don't forward to
+	 * userspace.
+	 *
+	 * The initialization is associated with opening the stream (not driver
+	 * init) considering we print a _NOTE about any throttling when closing
+	 * the stream instead of waiting until driver _fini which no one would
+	 * ever see.
+	 *
+	 * Using the same limiting factors as printk_ratelimit()
+	 */
+	ratelimit_state_init(&dev_priv->perf.oa.spurious_report_rs,
+			     5 * HZ, 10);
+	/* Since we use a DRM_NOTE for spurious reports it would be
+	 * inconsistent to let __ratelimit() automatically print a warning for
+	 * throttling.
+	 */
+	ratelimit_set_flags(&dev_priv->perf.oa.spurious_report_rs,
+			    RATELIMIT_MSG_ON_RELEASE);
+
 	stream->sample_size = sizeof(struct drm_i915_perf_record_header);
 
 	format_size = dev_priv->perf.oa.oa_formats[props->oa_format].size;