[PATCH 4.19 080/350] perf sched timehist: Fixed timestamp error when unable to confirm event sched_in time

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Yang Jihong <yangjihong@bytedance.com>

[ Upstream commit 39c243411bdb8fb35777adf49ee32549633c4e12 ]

If sched_in event for current task is not recorded, sched_in timestamp
will be set to end_time of time window interest, causing an error in
timestamp show. In this case, we choose to ignore this event.

Test scenario:

  perf[1229608] does not record the first sched_in event, run time and sch delay are both 0

  # perf sched timehist
  Samples of sched_switch event do not have callchains.
             time    cpu  task name                       wait time  sch delay   run time
                          [tid/pid]                          (msec)     (msec)     (msec)
  --------------- ------  ------------------------------  ---------  ---------  ---------
   2090450.763231 [0000]  perf[1229608]                       0.000      0.000      0.000
   2090450.763235 [0000]  migration/0[15]                     0.000      0.001      0.003
   2090450.763263 [0001]  perf[1229608]                       0.000      0.000      0.000
   2090450.763268 [0001]  migration/1[21]                     0.000      0.001      0.004
   2090450.763302 [0002]  perf[1229608]                       0.000      0.000      0.000
   2090450.763309 [0002]  migration/2[27]                     0.000      0.001      0.007
   2090450.763338 [0003]  perf[1229608]                       0.000      0.000      0.000
   2090450.763343 [0003]  migration/3[33]                     0.000      0.001      0.004

Before:

  arbitrarily specify a time window of interest, timestamp will be set to an incorrect value

  # perf sched timehist --time 100,200
  Samples of sched_switch event do not have callchains.
             time    cpu  task name                       wait time  sch delay   run time
                          [tid/pid]                          (msec)     (msec)     (msec)
  --------------- ------  ------------------------------  ---------  ---------  ---------
       200.000000 [0000]  perf[1229608]                       0.000      0.000      0.000
       200.000000 [0001]  perf[1229608]                       0.000      0.000      0.000
       200.000000 [0002]  perf[1229608]                       0.000      0.000      0.000
       200.000000 [0003]  perf[1229608]                       0.000      0.000      0.000
       200.000000 [0004]  perf[1229608]                       0.000      0.000      0.000
       200.000000 [0005]  perf[1229608]                       0.000      0.000      0.000
       200.000000 [0006]  perf[1229608]                       0.000      0.000      0.000
       200.000000 [0007]  perf[1229608]                       0.000      0.000      0.000

 After:

  # perf sched timehist --time 100,200
  Samples of sched_switch event do not have callchains.
             time    cpu  task name                       wait time  sch delay   run time
                          [tid/pid]                          (msec)     (msec)     (msec)
  --------------- ------  ------------------------------  ---------  ---------  ---------

Fixes: 853b74071110bed3 ("perf sched timehist: Add option to specify time window of interest")
Signed-off-by: Yang Jihong <yangjihong@bytedance.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: David Ahern <dsa@cumulusnetworks.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20240819024720.2405244-1-yangjihong@bytedance.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 tools/perf/builtin-sched.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
index 1c9e06c1d0089..cf8dc3910ef21 100644
--- a/tools/perf/builtin-sched.c
+++ b/tools/perf/builtin-sched.c
@@ -2553,9 +2553,12 @@ static int timehist_sched_change_event(struct perf_tool *tool,
 	 * - previous sched event is out of window - we are done
 	 * - sample time is beyond window user cares about - reset it
 	 *   to close out stats for time window interest
+	 * - If tprev is 0, that is, sched_in event for current task is
+	 *   not recorded, cannot determine whether sched_in event is
+	 *   within time window interest - ignore it
 	 */
 	if (ptime->end) {
-		if (tprev > ptime->end)
+		if (!tprev || tprev > ptime->end)
 			goto out;
 
 		if (t > ptime->end)
-- 
2.43.0