[Intel-gfx] [RFC 4/4] drm/i915/perf: Send system clock monotonic time in perf samples

[Sagar Arun Kamble]

From: Sourab Gupta <sourab.gupta at intel.com>

Currently, we have the ability to only forward the GPU timestamps in the
samples (which are generated via OA reports). This limits the ability to
correlate these samples with the system events.

An ability is therefore needed to report timestamps in different clock
domains, such as CLOCK_MONOTONIC, in the perf samples to be of more
practical use to the userspace. This ability becomes important
when we want to correlate/plot GPU events/samples with other system events
on the same timeline (e.g. vblank events, or timestamps when work was
submitted to kernel, etc.)

The patch here proposes a mechanism to achieve this. The correlation
between gpu time and system time is established using the timestamp clock
associated with the command stream, abstracted as timecounter/cyclecounter
to retrieve gpu/system time correlated values.

v2: Added i915_driver_init_late() function to capture the new late init
phase for perf (Chris)

v3: Removed cross-timestamp changes.

Signed-off-by: Sourab Gupta <sourab.gupta at intel.com>
Signed-off-by: Sagar Arun Kamble <sagar.a.kamble at intel.com>
Cc: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
Cc: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Sourab Gupta <sourab.gupta at intel.com>
Cc: Matthew Auld <matthew.auld at intel.com>
---
 drivers/gpu/drm/i915/i915_perf.c | 27 +++++++++++++++++++++++++++
 include/uapi/drm/i915_drm.h      |  7 +++++++
 2 files changed, 34 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
index 3b721d7..94ee924 100644
--- a/drivers/gpu/drm/i915/i915_perf.c
+++ b/drivers/gpu/drm/i915/i915_perf.c
@@ -336,6 +336,7 @@
 
 #define SAMPLE_OA_REPORT	BIT(0)
 #define SAMPLE_GPU_TS		BIT(1)
+#define SAMPLE_SYSTEM_TS	BIT(2)
 
 /**
  * struct perf_open_properties - for validated properties given to open a stream
@@ -622,6 +623,7 @@ static int append_oa_sample(struct i915_perf_stream *stream,
 	struct drm_i915_perf_record_header header;
 	u32 sample_flags = stream->sample_flags;
 	u64 gpu_ts = 0;
+	u64 system_ts = 0;
 
 	header.type = DRM_I915_PERF_RECORD_SAMPLE;
 	header.pad = 0;
@@ -647,6 +649,23 @@ static int append_oa_sample(struct i915_perf_stream *stream,
 
 		if (copy_to_user(buf, &gpu_ts, I915_PERF_TS_SAMPLE_SIZE))
 			return -EFAULT;
+		buf += I915_PERF_TS_SAMPLE_SIZE;
+	}
+
+	if (sample_flags & SAMPLE_SYSTEM_TS) {
+		gpu_ts = get_gpu_ts_from_oa_report(stream, report);
+		/*
+		 * XXX: timecounter_cyc2time considers time backwards if delta
+		 * timestamp is more than half the max ns time covered by
+		 * counter. It will be ~35min for 36 bit counter. If this much
+		 * sampling duration is needed we will have to update tc->nsec
+		 * by explicitly reading the timecounter (timecounter_read)
+		 * before this duration.
+		 */
+		system_ts = timecounter_cyc2time(&stream->tc, gpu_ts);
+
+		if (copy_to_user(buf, &system_ts, I915_PERF_TS_SAMPLE_SIZE))
+			return -EFAULT;
 	}
 
 	(*offset) += header.size;
@@ -2137,6 +2156,11 @@ static int i915_oa_stream_init(struct i915_perf_stream *stream,
 		stream->sample_size += I915_PERF_TS_SAMPLE_SIZE;
 	}
 
+	if (props->sample_flags & SAMPLE_SYSTEM_TS) {
+		stream->sample_flags |= SAMPLE_SYSTEM_TS;
+		stream->sample_size += I915_PERF_TS_SAMPLE_SIZE;
+	}
+
 	dev_priv->perf.oa.oa_buffer.format_size = format_size;
 	if (WARN_ON(dev_priv->perf.oa.oa_buffer.format_size == 0))
 		return -EINVAL;
@@ -2857,6 +2881,9 @@ static int read_properties_unlocked(struct drm_i915_private *dev_priv,
 		case DRM_I915_PERF_PROP_SAMPLE_GPU_TS:
 			props->sample_flags |= SAMPLE_GPU_TS;
 			break;
+		case DRM_I915_PERF_PROP_SAMPLE_SYSTEM_TS:
+			props->sample_flags |= SAMPLE_SYSTEM_TS;
+			break;
 		case DRM_I915_PERF_PROP_OA_METRICS_SET:
 			if (value == 0) {
 				DRM_DEBUG("Unknown OA metric set ID\n");
diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index 0b9249e..283859c 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -1453,6 +1453,12 @@ enum drm_i915_perf_property_id {
 	DRM_I915_PERF_PROP_SAMPLE_GPU_TS,
 
 	/**
+	 * This property requests inclusion of CLOCK_MONOTONIC system time in
+	 * the perf sample data.
+	 */
+	DRM_I915_PERF_PROP_SAMPLE_SYSTEM_TS,
+
+	/**
 	 * The value specifies which set of OA unit metrics should be
 	 * be configured, defining the contents of any OA unit reports.
 	 */
@@ -1539,6 +1545,7 @@ enum drm_i915_perf_record_type {
 	 *
 	 *     { u32 oa_report[]; } && DRM_I915_PERF_PROP_SAMPLE_OA
 	 *     { u64 gpu_timestamp; } && DRM_I915_PERF_PROP_SAMPLE_GPU_TS
+	 *     { u64 system_timestamp; } && DRM_I915_PERF_PROP_SAMPLE_SYSTEM_TS
 	 * };
 	 */
 	DRM_I915_PERF_RECORD_SAMPLE = 1,
-- 
1.9.1