[Intel-gfx] [RFC 2/4] drm/i915/perf: add new open param to configure polling of OA buffer

[Lionel Landwerlin]

This new parameter let's the application choose how often the OA
buffer should be checked on the CPU side for data availability. Longer
polling period tend to reduce CPU overhead if the application does not
care about somewhat real time data collection.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
---
 drivers/gpu/drm/i915/i915_drv.h  |  6 ++++++
 drivers/gpu/drm/i915/i915_perf.c | 27 +++++++++++++++++++++------
 include/uapi/drm/i915_drm.h      |  7 +++++++
 3 files changed, 34 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 09c4b5de141b..3669ed0a6376 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1348,6 +1348,12 @@ struct i915_perf_stream {
 	 * @oa_config: The OA configuration used by the stream.
 	 */
 	struct i915_oa_config *oa_config;
+
+	/**
+	 * @poll_oa_period: The period in nanoseconds at which the OA
+	 * buffer should be checked for available data.
+	 */
+	u64 poll_oa_period;
 };
 
 /**
diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
index d54142f1cff4..a8df58ec7d75 100644
--- a/drivers/gpu/drm/i915/i915_perf.c
+++ b/drivers/gpu/drm/i915/i915_perf.c
@@ -264,11 +264,11 @@
 #define OA_TAIL_MARGIN_NSEC	100000ULL
 #define INVALID_TAIL_PTR	0xffffffff
 
-/* frequency for checking whether the OA unit has written new reports to the
- * circular OA buffer...
+/* The default frequency for checking whether the OA unit has written new
+ * reports to the circular OA buffer...
  */
-#define POLL_FREQUENCY 200
-#define POLL_PERIOD (NSEC_PER_SEC / POLL_FREQUENCY)
+#define DEFAULT_POLL_FREQUENCY 200
+#define DEFAULT_POLL_PERIOD (NSEC_PER_SEC / DEFAULT_POLL_FREQUENCY)
 
 /* for sysctl proc_dointvec_minmax of dev.i915.perf_stream_paranoid */
 static int zero;
@@ -345,6 +345,8 @@ static const struct i915_oa_format gen8_plus_oa_formats[I915_OA_FORMAT_MAX] = {
  * @oa_format: An OA unit HW report format
  * @oa_periodic: Whether to enable periodic OA unit sampling
  * @oa_period_exponent: The OA unit sampling period is derived from this
+ * @poll_oa_period: The period at which the CPU will check for OA data
+ * availability
  *
  * As read_properties_unlocked() enumerates and validates the properties given
  * to open a stream of metrics the configuration is built up in the structure
@@ -361,6 +363,7 @@ struct perf_open_properties {
 	int oa_format;
 	bool oa_periodic;
 	int oa_period_exponent;
+	u64 poll_oa_period;
 };
 
 static void free_oa_config(struct drm_i915_private *dev_priv,
@@ -1902,7 +1905,7 @@ static void i915_oa_stream_enable(struct i915_perf_stream *stream)
 
 	if (dev_priv->perf.oa.periodic)
 		hrtimer_start(&dev_priv->perf.oa.poll_check_timer,
-			      ns_to_ktime(POLL_PERIOD),
+			      ns_to_ktime(stream->poll_oa_period),
 			      HRTIMER_MODE_REL_PINNED);
 }
 
@@ -2266,13 +2269,15 @@ static enum hrtimer_restart oa_poll_check_timer_cb(struct hrtimer *hrtimer)
 	struct drm_i915_private *dev_priv =
 		container_of(hrtimer, typeof(*dev_priv),
 			     perf.oa.poll_check_timer);
+	struct i915_perf_stream *stream = dev_priv->perf.oa.exclusive_stream;
 
 	if (oa_buffer_check_unlocked(dev_priv)) {
 		dev_priv->perf.oa.pollin = true;
 		wake_up(&dev_priv->perf.oa.poll_wq);
 	}
 
-	hrtimer_forward_now(hrtimer, ns_to_ktime(POLL_PERIOD));
+	hrtimer_forward_now(hrtimer,
+			    ns_to_ktime(stream->poll_oa_period));
 
 	return HRTIMER_RESTART;
 }
@@ -2593,6 +2598,7 @@ i915_perf_open_ioctl_locked(struct drm_i915_private *dev_priv,
 
 	stream->dev_priv = dev_priv;
 	stream->ctx = specific_ctx;
+	stream->poll_oa_period = props->poll_oa_period;
 
 	ret = i915_oa_stream_init(stream, param, props);
 	if (ret)
@@ -2669,6 +2675,7 @@ static int read_properties_unlocked(struct drm_i915_private *dev_priv,
 	u32 i;
 
 	memset(props, 0, sizeof(struct perf_open_properties));
+	props->poll_oa_period = DEFAULT_POLL_PERIOD;
 
 	if (!n_props) {
 		DRM_DEBUG("No i915 perf properties given\n");
@@ -2772,6 +2779,14 @@ static int read_properties_unlocked(struct drm_i915_private *dev_priv,
 			props->oa_periodic = true;
 			props->oa_period_exponent = value;
 			break;
+		case DRM_I915_PERF_PROP_POLL_OA_DELAY:
+			if (value < 100000 /* 100us */) {
+				DRM_DEBUG("OA availability timer too small (%lluns < 100us)\n",
+					  value);
+				return -EINVAL;
+			}
+			props->poll_oa_period = value;
+			break;
 		case DRM_I915_PERF_PROP_MAX:
 			MISSING_CASE(id);
 			return -EINVAL;
diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index 298b2e197744..7191236ad7f2 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -1540,6 +1540,13 @@ enum drm_i915_perf_property_id {
 	 */
 	DRM_I915_PERF_PROP_OA_EXPONENT,
 
+	/**
+	 * Specifying this property sets up a hrtimer in nanoseconds at which
+	 * the i915 driver will check the OA buffer for available data. Values
+	 * below 100 microseconds are not allowed.
+	 */
+	DRM_I915_PERF_PROP_POLL_OA_DELAY,
+
 	DRM_I915_PERF_PROP_MAX /* non-ABI */
 };
 
-- 
2.20.1