drm/i915: Add a tracepoint for the shrinker

Often it is very useful to know why we suddenly purge vast tracts of
memory and surprisingly up until now we didn't even have a tracepoint
for when we shrink our memory.

Note that there are slab_start/end tracepoints already, but those
don't cover the internal recursion when we directly call into our
shrinker code. Hence a separate tracepoint seems justified. Also note
that we don't really need a separate tracepoint for the actual amount
of pages freed since we already have an unbind tracpoint for that.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
[danvet: Add a note that there's also slab_start/end and why they're
insufficient.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_shrinker.c

@@ -85,6 +85,8 @@ i915_gem_shrink(struct drm_i915_private *dev_priv,
 	}, *phase;
 	unsigned long count = 0;
 
+	trace_i915_gem_shrink(dev_priv, target, flags);
+
 	/*
 	 * As we may completely rewrite the (un)bound list whilst unbinding
 	 * (due to retiring requests) we have to strictly process only

drivers/gpu/drm/i915/i915_trace.h

@@ -107,6 +107,26 @@ TRACE_EVENT(i915_gem_object_create,
 	    TP_printk("obj=%p, size=%u", __entry->obj, __entry->size)
 );
 
+TRACE_EVENT(i915_gem_shrink,
+	    TP_PROTO(struct drm_i915_private *i915, unsigned long target, unsigned flags),
+	    TP_ARGS(i915, target, flags),
+
+	    TP_STRUCT__entry(
+			     __field(int, dev)
+			     __field(unsigned long, target)
+			     __field(unsigned, flags)
+			     ),
+
+	    TP_fast_assign(
+			   __entry->dev = i915->dev->primary->index;
+			   __entry->target = target;
+			   __entry->flags = flags;
+			   ),
+
+	    TP_printk("dev=%d, target=%lu, flags=%x",
+		      __entry->dev, __entry->target, __entry->flags)
+);
+
 TRACE_EVENT(i915_vma_bind,
 	    TP_PROTO(struct i915_vma *vma, unsigned flags),
 	    TP_ARGS(vma, flags),