When perf-sched enables the call-graph recording, sample_type of dummy
event does not have PERF_SAMPLE_CALLCHAIN, timehist_check_attr() checks
that the evsel does not have a callchain, and set show_callchain to 0.

Currently perf sched timehist only saves callchain when processing
sched:sched_switch event, timehist_check_attr() only needs to determine
whether the event has PERF_SAMPLE_CALLCHAIN.

Before:
  # perf sched record -g true
  [ perf record: Woken up 0 times to write data ]
  [ perf record: Captured and wrote 4.153 MB perf.data (7536 samples) ]
  # perf sched timehist
  Samples do not have callchains.
             time    cpu  task name                       wait time  sch delay   run time
                          [tid/pid]                          (msec)     (msec)     (msec)
  --------------- ------  ------------------------------  ---------  ---------  ---------
    147851.826019 [0000]  perf[285035]                        0.000      0.000      0.000
    147851.826029 [0000]  migration/0[15]                     0.000      0.003      0.009
    147851.826063 [0001]  perf[285035]                        0.000      0.000      0.000
    147851.826069 [0001]  migration/1[21]                     0.000      0.003      0.006
  <SNIP>

After:
  # perf sched record -g true
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 2.572 MB perf.data (822 samples) ]
  # perf sched timehist
             time    cpu  task name                       wait time  sch delay   run time
                          [tid/pid]                          (msec)     (msec)     (msec)
  --------------- ------  ------------------------------  ---------  ---------  ---------
    144193.035164 [0000]  perf[277062]                        0.000      0.000      0.000    __traceiter_sched_switch <- __traceiter_sched_switch <- __sched_text_start <- preempt_schedule_common <- __cond_resched <- __wait_for_common <- wait_for_completion
    144193.035174 [0000]  migration/0[15]                     0.000      0.003      0.009    __traceiter_sched_switch <- __traceiter_sched_switch <- __sched_text_start <- smpboot_thread_fn <- kthread <- ret_from_fork
    144193.035207 [0001]  perf[277062]                        0.000      0.000      0.000    __traceiter_sched_switch <- __traceiter_sched_switch <- __sched_text_start <- preempt_schedule_common <- __cond_resched <- __wait_for_common <- wait_for_completion
    144193.035214 [0001]  migration/1[21]                     0.000      0.003      0.007    __traceiter_sched_switch <- __traceiter_sched_switch <- __sched_text_start <- smpboot_thread_fn <- kthread <- ret_from_fork
  <SNIP>

Fixes: 9c95e4ef0657 ("perf evlist: Add evlist__findnew_tracking_event() helper")
Signed-off-by: Yang Jihong <yangjihong@bytedance.com>
Reviewed-by: Ian Rogers <irogers@google.com>
---
 tools/perf/builtin-sched.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
index b248c433529a..1bfb22347371 100644
--- a/tools/perf/builtin-sched.c
+++ b/tools/perf/builtin-sched.c
@@ -2963,8 +2963,11 @@ static int timehist_check_attr(struct perf_sched *sched,
 			return -1;
 		}
 
-		if (sched->show_callchain && !evsel__has_callchain(evsel)) {
-			pr_info("Samples do not have callchains.\n");
+		/* only need to save callchain related to sched_switch event */
+		if (sched->show_callchain &&
+		    evsel__name_is(evsel, "sched:sched_switch") &&
+		    !evsel__has_callchain(evsel)) {
+			pr_info("Samples of sched_switch event do not have callchains.\n");
 			sched->show_callchain = 0;
 			symbol_conf.use_callchain = 0;
 		}
-- 
2.25.1