perf/core: Add speculation info to branch entries

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@google.com>
Signed-off-by: Sandipan Das <sandipan.das@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/834088c302faf21c7b665031dd111f424e509a64.1660211399.git.sandipan.das@amd.com

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index ee8b9ec..ae30c61 100644 (file)
--- 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 03b3700..30a4723 100644 (file)
--- 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 {