[PATCH V3 01/13] perf/core: Add new branch sample type for LBR TOS

[kan . liang]

From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>

In LBR call stack mode, the depth of reconstructed LBR call stack limits
to the number of LBR registers. With LBR Top-of-Stack (TOS) information,
perf tool may stitch the stacks of two samples. The reconstructed LBR
call stack can break the HW limitation.

Add a new branch sample type to retrieve LBR TOS.

Only when the new branch sample type is set, the TOS information is
dumped into the PERF_SAMPLE_BRANCH_STACK output.
Perf tool should check the attr.branch_sample_type, and apply the
corresponding format for PERF_SAMPLE_BRANCH_STACK samples.
Otherwise, some user case may be broken. For example, users may parse a
perf.data, which include the new branch sample type, with an old version
perf tool (without the check). Users probably get incorrect information
without any warning.

Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
---
 include/linux/perf_event.h      |  2 ++
 include/uapi/linux/perf_event.h | 10 +++++++++-
 kernel/events/core.c            | 11 +++++++++++
 3 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 61448c19a132..2b229ea1cc15 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -92,6 +92,7 @@ struct perf_raw_record {
 /*
  * branch stack layout:
  *  nr: number of taken branches stored in entries[]
+ *  tos: Top-of-Stack (TOS) information. PMU specific data.
  *
  * Note that nr can vary from sample to sample
  * branches (to, from) are stored from most recent
@@ -100,6 +101,7 @@ struct perf_raw_record {
  */
 struct perf_branch_stack {
 	__u64				nr;
+	__u64				tos; /* PMU specific data */
 	struct perf_branch_entry	entries[0];
 };
 
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index bb7b271397a6..b1f022190571 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -180,6 +180,8 @@ enum perf_branch_sample_type_shift {
 
 	PERF_SAMPLE_BRANCH_TYPE_SAVE_SHIFT	= 16, /* save branch type */
 
+	PERF_SAMPLE_BRANCH_LBR_TOS_SHIFT	= 17, /* save LBR TOS */
+
 	PERF_SAMPLE_BRANCH_MAX_SHIFT		/* non-ABI */
 };
 
@@ -207,6 +209,8 @@ enum perf_branch_sample_type {
 	PERF_SAMPLE_BRANCH_TYPE_SAVE	=
 		1U << PERF_SAMPLE_BRANCH_TYPE_SAVE_SHIFT,
 
+	PERF_SAMPLE_BRANCH_LBR_TOS	= 1U << PERF_SAMPLE_BRANCH_LBR_TOS_SHIFT,
+
 	PERF_SAMPLE_BRANCH_MAX		= 1U << PERF_SAMPLE_BRANCH_MAX_SHIFT,
 };
 
@@ -849,7 +853,11 @@ enum perf_event_type {
 	 *	  char                  data[size];}&& PERF_SAMPLE_RAW
 	 *
 	 *	{ u64                   nr;
-	 *        { u64 from, to, flags } lbr[nr];} && PERF_SAMPLE_BRANCH_STACK
+	 *        { u64 from, to, flags } lbr[nr];
+	 *
+	 *        # only available if PERF_SAMPLE_BRANCH_LBR_TOS is set
+	 *        u64			tos;
+	 *      } && PERF_SAMPLE_BRANCH_STACK
 	 *
 	 * 	{ u64			abi; # enum perf_sample_regs_abi
 	 * 	  u64			regs[weight(mask)]; } && PERF_SAMPLE_REGS_USER
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 9ec0b0bfddbd..18b0a7d2c67e 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6343,6 +6343,11 @@ static void perf_output_read(struct perf_output_handle *handle,
 		perf_output_read_one(handle, event, enabled, running);
 }
 
+static inline bool perf_sample_save_lbr_tos(struct perf_event *event)
+{
+	return event->attr.branch_sample_type & PERF_SAMPLE_BRANCH_LBR_TOS;
+}
+
 void perf_output_sample(struct perf_output_handle *handle,
 			struct perf_event_header *header,
 			struct perf_sample_data *data,
@@ -6432,6 +6437,8 @@ void perf_output_sample(struct perf_output_handle *handle,
 
 			perf_output_put(handle, data->br_stack->nr);
 			perf_output_copy(handle, data->br_stack->entries, size);
+			if (perf_sample_save_lbr_tos(event))
+				perf_output_put(handle, data->br_stack->tos);
 		} else {
 			/*
 			 * we always store at least the value of nr
@@ -6619,7 +6626,11 @@ void perf_prepare_sample(struct perf_event_header *header,
 		if (data->br_stack) {
 			size += data->br_stack->nr
 			      * sizeof(struct perf_branch_entry);
+
+			if (perf_sample_save_lbr_tos(event))
+				size += sizeof(u64);
 		}
+
 		header->size += size;
 	}
 
-- 
2.17.1