[Intel-gfx] [PATCH] drm/i915: Add a tracepoint for using a semaphore

[Chris Wilson]

So that we can find the callers who introduce a ring stall. A single
ring stall is not too unwelcome, the right issue becomes when they start
to interlock and prevent any concurrent work. That, however, is a little
tricker to detect with a mere tracepoint!

v2: Rebrand it as a ring event, rather than an object event.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem.c   |  2 ++
 drivers/gpu/drm/i915/i915_trace.h | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 85537d1..a9a6baa 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2698,6 +2698,8 @@ i915_gem_object_sync(struct drm_i915_gem_object *obj,
 	if (ret)
 		return ret;
 
+	trace_i915_gem_ring_sync_to(from, to);
+
 	ret = to->sync_to(to, from, seqno);
 	if (!ret)
 		/* We use last_read_seqno because sync_to()
diff --git a/drivers/gpu/drm/i915/i915_trace.h b/drivers/gpu/drm/i915/i915_trace.h
index feaacbb..163774a 100644
--- a/drivers/gpu/drm/i915/i915_trace.h
+++ b/drivers/gpu/drm/i915/i915_trace.h
@@ -235,6 +235,25 @@ TRACE_EVENT(i915_gem_evict_everything,
 	    TP_printk("dev=%d", __entry->dev)
 );
 
+TRACE_EVENT(i915_gem_ring_sync_to,
+	    TP_PROTO(struct intel_ring_buffer *from, struct intel_ring_buffer *to),
+	    TP_ARGS(from, to),
+
+	    TP_STRUCT__entry(
+			     __field(u32, dev)
+			     __field(u32, sync_from)
+			     __field(u32, sync_to)
+			     ),
+
+	    TP_fast_assign(
+			   __entry->dev = from->dev->primary->index;
+			   __entry->sync_from = from->id;
+			   __entry->sync_to = to->id;
+			   ),
+
+	    TP_printk("dev=%u, sync-from=%u, sync-to=%u", __entry->dev, __entry->sync_from, __entry->sync_to)
+);
+
 TRACE_EVENT(i915_gem_ring_dispatch,
 	    TP_PROTO(struct intel_ring_buffer *ring, u32 flags),
 	    TP_ARGS(ring, flags),
-- 
1.8.4.rc3