In redhat perftool testsuite, observed fail for this test:
    -- [ FAIL ] -- perf_sched :: test_timehist :: --with-summary (output regexp parsing)

This led to analysis of "perf sched timehist" summary options.

  # perf sched record -a -o ./perf.data -- sleep 0.1
   This will record using perf sched record

perf sched timeliest has two options "-s" and "-S"
  # perf sched -i ./perf.data timehist -S
 -S : Captures summary also at the end

  # perf sched -i ./perf.data timehist -s
 -s : Captures only summary

The test saves -s result which has only summary and compares with
summary which comes at the end from -S . Since there is a difference
in these two, test fails.

Checking the behaviour change in -S and -s results, difference is:

                  rcu_sched[16]       2          4        0.013      0.001       0.003       0.006   33.23       0
               migration/11[73]       2          1        0.006      0.006       0.006       0.006    0.00       0
                migration/3[33]       2          1        0.006      0.006       0.006       0.006    0.00       0
 -               :216753[216753]      -1          1        0.041      0.041       0.041       0.041    0.00       0
 +                 sleep[216753]      -1          1        0.041      0.041       0.041       0.041    0.00       0
                migration/8[58]       2          1        0.005      0.005       0.005       0.005    0.00       0
            NetworkManager[811]       1          2        0.089      0.028       0.044       0.060   36.06       0
               migration/13[83]       2          1        0.005      0.005       0.005       0.005    0.00       0

Here 216753 is pid for sleep which is a zombie process. This is
happening in latest kernel due to an update in "-S" result.
In -S, the process name appears in the results "sleep[216753]",
where as in the -s, only pid is present in the summary result
":216753[216753]".

After commit 39f473f6d0b2 ("perf sched timehist: decode process names
of processes in zombie state")
for -S option, if process name is using pid, it uses different way to
set it. So that we get the process name and not just Pid.

This change went in only for timehist_print_sample() function.
Add this improvement in generic place so that even -s option (which
captures summary) also will have meaningful information.

Acked-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Venkat Rao Bagalkote <redacted>
Signed-off-by: Athira Rajeev <redacted>
---
Changelog
v1 -> v2:
- Rebased on top of latest perf-tools-next
- Since there is no change in logic, carried Acked-by from
Namhyung Kim and Tested-by from Venkat Rao Bagalkote

 tools/perf/builtin-sched.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
index b7ccdc6a985d..5d3761a27e67 100644
--- a/tools/perf/builtin-sched.c
+++ b/tools/perf/builtin-sched.c

@@ -2259,12 +2259,6 @@ static void timehist_print_sample(struct perf_sched *sched,
 		printf(" ");
 	}
 
-	if (!thread__comm_set(thread)) {
-		const char *prev_comm = perf_sample__strval(sample, "prev_comm");
-
-		thread__set_comm(thread, prev_comm, sample->time);
-        }
-
 	printf(" %-*s ", comm_width, timehist_get_commstr(thread));
 
 	if (sched->show_prio)

@@ -2965,6 +2959,16 @@ static int timehist_sched_change_event(const struct perf_tool *tool,
 			thread__zput(itr->last_thread);
 		}
 
+		/*
+		 * If the process name is not set for the thread, use "prev_comm"
+		 * to set it. Otherwise the sched summary will have just pid information
+		 */
+		if (!thread__comm_set(thread)) {
+			const char *prev_comm = perf_sample__strval(sample, "prev_comm");
+
+			thread__set_comm(thread, prev_comm, sample->time);
+		}
+
 		if (!sched->summary_only)
 			timehist_print_sample(sched, sample, &al, thread, t, state);
 	}

-- 
2.52.0