[Intel-gfx] [PATCH v3 8/9] drm/i915/perf: add flushing ioctl

[Lionel Landwerlin]

With the currently available parameters for the i915-perf stream,
there are still situations that are not well covered :

If an application opens the stream with polling disable or at very low
frequency and OA interrupt enabled, no data will be available even
though somewhere between nothing and half of the OA buffer worth of
data might have landed in memory.

To solve this issue we have a new flush ioctl on the perf stream that
forces the i915-perf driver to look at the state of the buffer when
called and makes any data available through both poll() & read() type
syscalls.

v2: Version the ioctl (Joonas)

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
---
 drivers/gpu/drm/i915/i915_perf.c | 17 +++++++++++++++++
 include/uapi/drm/i915_drm.h      | 21 +++++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
index 39801a6e3021..7067a0f1700e 100644
--- a/drivers/gpu/drm/i915/i915_perf.c
+++ b/drivers/gpu/drm/i915/i915_perf.c
@@ -2431,6 +2431,20 @@ static void i915_perf_disable_locked(struct i915_perf_stream *stream)
 		stream->ops->disable(stream);
 }
 
+/**
+ * i915_perf_flush_data - handle `I915_PERF_IOCTL_FLUSH_DATA` ioctl
+ * @stream: An enabled i915 perf stream
+ *
+ * The intention is to flush all the data available for reading from the OA
+ * buffer
+ */
+static void i915_perf_flush_data(struct i915_perf_stream *stream)
+{
+	struct drm_i915_private *dev_priv = stream->dev_priv;
+
+	dev_priv->perf.oa.pollin = oa_buffer_check(stream->dev_priv, true);
+}
+
 /**
  * i915_perf_ioctl - support ioctl() usage with i915 perf stream FDs
  * @stream: An i915 perf stream
@@ -2454,6 +2468,9 @@ static long i915_perf_ioctl_locked(struct i915_perf_stream *stream,
 	case I915_PERF_IOCTL_DISABLE:
 		i915_perf_disable_locked(stream);
 		return 0;
+	case I915_PERF_IOCTL_FLUSH_DATA:
+		i915_perf_flush_data(stream);
+		return 0;
 	}
 
 	return -EINVAL;
diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index d04ce7ba6bd2..54cd3099b2d9 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -1709,6 +1709,27 @@ struct drm_i915_perf_open_param {
  */
 #define I915_PERF_IOCTL_DISABLE	_IO('i', 0x1)
 
+/**
+ * Actively check the availability of data from a stream.
+ *
+ * A stream data availability can be driven by two types of events :
+ *
+ *   - if enabled, the kernel's hrtimer checking the amount of available data
+ *     in the OA buffer through head/tail registers.
+ *
+ *   - if enabled, the OA unit's interrupt mechanism
+ *
+ * The kernel hrtimer incur a cost of running callback at fixed time
+ * intervals, while the OA interrupt might only happen rarely. In the
+ * situation where the application has disabled the kernel's hrtimer and only
+ * uses the OA interrupt to know about available data, the application can
+ * request an active check of the available OA data through this ioctl. This
+ * will make any data in the OA buffer available with either poll() or read().
+ *
+ * This ioctl is available in perf revision 2.
+ */
+#define I915_PERF_IOCTL_FLUSH_DATA _IO('i', 0x2)
+
 /**
  * Common to all i915 perf records
  */
-- 
2.20.1