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Subject[tip: perf/core] perf/core: Add speculation info to branch entries
The following commit has been merged into the perf/core branch of tip:

Commit-ID: 93315e46b000fc80fff5d53c3f444417fb3df6de
Gitweb: https://git.kernel.org/tip/93315e46b000fc80fff5d53c3f444417fb3df6de
Author: Sandipan Das <sandipan.das@amd.com>
AuthorDate: Thu, 11 Aug 2022 18:00:00 +05:30
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Sat, 27 Aug 2022 00:05:45 +02:00

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
---
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 ee8b9ec..ae30c61 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 03b3700..30a4723 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 {
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