[PATCH 22/25] perf cs-etm: Centralize sample history collection

[Leo Yan]

Extract thread lookup, branch history collection and history consumption
from cs_etm__process_sample() into cs_etm__save_sample_history(). This
separates collecting decoded history from attaching it to a perf sample
and provides a common place for adding callchain collection.

Keep history collection to consume branch history so later samples
cannot reuse an earlier trace window. Use the session stored in the
auxtrace state and remove the redundant process_sample() argument.

Assisted-by: Codex:gpt-6
Signed-off-by: Leo Yan <leo.yan@xxxxxxx>
---
 tools/perf/util/cs-etm.c | 46 ++++++++++++++++++++++++----------------------
 1 file changed, 24 insertions(+), 22 deletions(-)

diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
index e78c8e089f38eae34faa12bbd2f899f1f72acce4..815a22cedc49e9281b7087f01355bb71b5e41c57 100644
--- a/tools/perf/util/cs-etm.c
+++ b/tools/perf/util/cs-etm.c
@@ -2048,6 +2048,26 @@ static int cs_etm__exception(struct cs_etm_traceid_queue *tidq)
 	return 0;
 }
 
+static int cs_etm__save_sample_history(struct cs_etm_auxtrace *etm,
+				       const struct perf_sample *sample)
+{
+	struct machine *machine = &etm->session->machines.host;
+	struct thread *thread;
+
+	thread = machine__findnew_thread(machine, sample->pid, sample->tid);
+	if (!thread)
+		return -ENOMEM;
+
+	/* Consume branch history so later samples cannot reuse the same window. */
+	thread_stack__br_sample_late(thread, sample->cpu, etm->br_stack,
+				     etm->br_stack_sz, sample->ip,
+				     machine__kernel_start(machine));
+	thread_stack__br_stack_consume(thread, sample->cpu);
+
+	thread__put(thread);
+	return 0;
+}
+
 static int cs_etm__flush(struct cs_etm_queue *etmq,
 			 struct cs_etm_traceid_queue *tidq)
 {
@@ -3088,11 +3108,8 @@ static int cs_etm__br_stack_init(struct cs_etm_auxtrace *etm,
  * the kernel; its thread and trace window still identify valid history.
  */
 static int cs_etm__process_sample(struct cs_etm_auxtrace *etm,
-				  struct perf_session *session,
 				  struct perf_sample *sample)
 {
-	struct machine *machine = &session->machines.host;
-	struct thread *thread;
 	int err;
 
 	if (!etm->synth_opts.add_last_branch || sample->branch_stack ||
@@ -3117,28 +3134,13 @@ static int cs_etm__process_sample(struct cs_etm_auxtrace *etm,
 	if (err)
 		return err;
 
-	thread = machine__findnew_thread(machine, sample->pid, sample->tid);
-	if (!thread)
-		return -ENOMEM;
-
-	/*
-	 * Take the branch history rather than copying it. The trace window
-	 * belongs to the sample that ends it, so once it has been attached a
-	 * later sample with nothing newly decoded finds an empty stack rather
-	 * than being given an earlier window's branches. That is the common
-	 * case whenever the trace is duty cycled, by AUX pause/resume or by
-	 * ETM strobing.
-	 */
-	thread_stack__br_sample_late(thread, sample->cpu, etm->br_stack,
-				     etm->br_stack_sz, sample->ip,
-				     machine__kernel_start(machine));
-	thread_stack__br_stack_consume(thread, sample->cpu);
+	err = cs_etm__save_sample_history(etm, sample);
+	if (err)
+		return err;
 
 	if (etm->br_stack->nr)
 		sample->branch_stack = etm->br_stack;
 
-	thread__put(thread);
-
 	return 0;
 }
 
@@ -3181,7 +3183,7 @@ static int cs_etm__process_event(struct perf_session *session,
 		return cs_etm__process_switch_cpu_wide(etm, event);
 
 	case PERF_RECORD_SAMPLE:
-		return cs_etm__process_sample(etm, session, sample);
+		return cs_etm__process_sample(etm, sample);
 
 	case PERF_RECORD_AUX:
 		/*

-- 
2.34.1