[PATCH 12/13] perf/core: Add speculation info to branch entries

[Sandipan Das]

Add a new "spec" bitfield to branch entries for providing speculation
information. This will be populated using hints provided by branch sampling
features on supported hardware. The following cases are covered:

  * No branch speculation information is available
  * Branch is speculative but taken on the wrong path
  * Branch is non-speculative but taken on the correct path
  * Branch is speculative and taken on the correct path

Suggested-by: Stephane Eranian <eranian@xxxxxxxxxx>
Signed-off-by: Sandipan Das <sandipan.das@xxxxxxx>
---
 include/linux/perf_event.h      |  1 +
 include/uapi/linux/perf_event.h | 15 ++++++++++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index ee8b9ecdc03b..ae30c61957d2 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1078,6 +1078,7 @@ static inline void perf_clear_branch_entry_bitfields(struct perf_branch_entry *b
 	br->abort = 0;
 	br->cycles = 0;
 	br->type = 0;
+	br->spec = PERF_BR_SPEC_NA;
 	br->reserved = 0;
 }
 
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 0474ee362151..9656733a95a5 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -256,6 +256,17 @@ enum {
 	PERF_BR_MAX,
 };
 
+/*
+ * Common branch speculation outcome classification
+ */
+enum {
+	PERF_BR_SPEC_NA			= 0,	/* Not available */
+	PERF_BR_SPEC_WRONG_PATH		= 1,	/* Speculative but on wrong path */
+	PERF_BR_NON_SPEC_CORRECT_PATH	= 2,	/* Non-speculative but on correct path */
+	PERF_BR_SPEC_CORRECT_PATH	= 3,	/* Speculative and on correct path */
+	PERF_BR_SPEC_MAX,
+};
+
 #define PERF_SAMPLE_BRANCH_PLM_ALL \
 	(PERF_SAMPLE_BRANCH_USER|\
 	 PERF_SAMPLE_BRANCH_KERNEL|\
@@ -1363,6 +1374,7 @@ union perf_mem_data_src {
  *     abort: aborting a hardware transaction
  *    cycles: cycles from last branch (or 0 if not supported)
  *      type: branch type
+ *      spec: branch speculation info (or 0 if not supported)
  */
 struct perf_branch_entry {
 	__u64	from;
@@ -1373,7 +1385,8 @@ struct perf_branch_entry {
 		abort:1,    /* transaction abort */
 		cycles:16,  /* cycle count to last branch */
 		type:4,     /* branch type */
-		reserved:40;
+		spec:2,     /* branch speculation info */
+		reserved:38;
 };
 
 union perf_sample_weight {
-- 
2.34.1