[RFC PATCH 1/8] tracing/gpu: modify gpu_mem_total

[Gurchetan Singh]

The existing gpu_mem_total tracepoint [1] is not currently used by
any in-tree consumers, we should add some.

In addition, there's a desire to report imported memory via the
counters too [2].

To do this, we'll have to redefine the event to:

a) Change 'pid' to 'ctx_id'

The reason is  DRM subsystem is created with GEM objects, DRM devices
and DRM files in mind.  A GEM object is associated with DRM device,
and it may be shared between one or more DRM files.

Per-instance (or "context") counters make more sense than per-process
counters for DRM.  For GPUs that per process counters (kgsl), this
change is backwards compatible.

b) add an "import_mem_total" field

We're just appending a field, so no problem here.  Change "size" to
"mem_total" as well (name changes are backwards compatible).

[1] https://lore.kernel.org/r/20200302234840.57188-1-zzyiwei@google.com/
[2] https://www.spinics.net/lists/kernel/msg4062769.html

Signed-off-by: Gurchetan Singh <gurchetansingh at chromium.org>
---
 include/trace/events/gpu_mem.h | 61 ++++++++++++++++++++++++----------
 1 file changed, 43 insertions(+), 18 deletions(-)

diff --git a/include/trace/events/gpu_mem.h b/include/trace/events/gpu_mem.h
index 26d871f96e94..198b87f50356 100644
--- a/include/trace/events/gpu_mem.h
+++ b/include/trace/events/gpu_mem.h
@@ -14,41 +14,66 @@
 #include <linux/tracepoint.h>
 
 /*
- * The gpu_memory_total event indicates that there's an update to either the
- * global or process total gpu memory counters.
+ * The gpu_mem_total event indicates that there's an update to local or
+ * global gpu memory counters.
  *
- * This event should be emitted whenever the kernel device driver allocates,
- * frees, imports, unimports memory in the GPU addressable space.
+ * This event should be emitted whenever a GPU device (ctx_id == 0):
  *
- * @gpu_id: This is the gpu id.
+ *   1) allocates memory.
+ *   2) frees memory.
+ *   3) imports memory from an external exporter.
  *
- * @pid: Put 0 for global total, while positive pid for process total.
+ * OR when a GPU device instance (ctx_id != 0):
  *
- * @size: Size of the allocation in bytes.
+ *   1) allocates or acquires a reference to memory from another instance.
+ *   2) frees or releases a reference to memory from another instance.
+ *   3) imports memory from another GPU device instance.
  *
+ * When ctx_id == 0, both mem_total and import_mem_total total counters
+ * represent a global total.  When ctx_id == 0, these counters represent
+ * an instance specifical total.
+ *
+ * Note allocation does not necessarily mean backing the memory with pages.
+ *
+ * @gpu_id: unique ID of the GPU.
+ *
+ * @ctx_id: an ID for specific instance of the GPU device.
+ *
+ * @mem_total: - total size of memory known to a GPU device, including
+ *		 imports (ctx_id == 0)
+ *	       - total size of memory known to a GPU device instance
+ *		 (ctx_id != 0)
+ *
+ * @import_mem_total: - size of memory imported from outside GPU
+ *			device (ctx_id == 0)
+ *		      - size of memory imported into GPU device instance.
+ *			(ctx_id == 0)
  */
 TRACE_EVENT(gpu_mem_total,
 
-	TP_PROTO(uint32_t gpu_id, uint32_t pid, uint64_t size),
+	TP_PROTO(u32 gpu_id, u32 ctx_id, u64 mem_total, u64 import_mem_total),
 
-	TP_ARGS(gpu_id, pid, size),
+	TP_ARGS(gpu_id, ctx_id, mem_total, import_mem_total),
 
 	TP_STRUCT__entry(
-		__field(uint32_t, gpu_id)
-		__field(uint32_t, pid)
-		__field(uint64_t, size)
+		__field(u32, gpu_id)
+		__field(u32, ctx_id)
+		__field(u64, mem_total)
+		__field(u64, import_mem_total)
 	),
 
 	TP_fast_assign(
 		__entry->gpu_id = gpu_id;
-		__entry->pid = pid;
-		__entry->size = size;
+		__entry->ctx_id = ctx_id;
+		__entry->mem_total = mem_total;
+		__entry->import_mem_total = import_mem_total;
 	),
 
-	TP_printk("gpu_id=%u pid=%u size=%llu",
-		__entry->gpu_id,
-		__entry->pid,
-		__entry->size)
+	TP_printk("gpu_id=%u, ctx_id=%u, mem total=%llu, mem import total=%llu",
+		  __entry->gpu_id,
+		  __entry->ctx_id,
+		  __entry->mem_total,
+		  __entry->import_mem_total)
 );
 
 #endif /* _TRACE_GPU_MEM_H */
-- 
2.25.1