linux-kernel - [tip: perf/core] perf/core: Add speculation info to branch entries

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Message-ID: <166155215416.401.7378423137712801227.tip-bot2@tip-bot2>
Date:   Fri, 26 Aug 2022 22:15:54 -0000
From:   "tip-bot2 for Sandipan Das" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Stephane Eranian <eranian@...gle.com>,
        Sandipan Das <sandipan.das@....com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
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@....com>
AuthorDate:    Thu, 11 Aug 2022 18:00:00 +05:30
Committer:     Peter Zijlstra <peterz@...radead.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@...gle.com>
Signed-off-by: Sandipan Das <sandipan.das@....com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.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 {