When --time option is given with a value outside recorded time, the last sample time (tprev) was set to that value and run time calculation might be incorrect. This is a problem of the first samples for each cpus since it would skip the runtime update when tprev is 0. But with --time option it had non-zero (which is invalid) value so the calculation is also incorrect.
For example, let's see the followging: $ perf sched timehist time cpu task name wait time sch delay run time [tid/pid] (msec) (msec) (msec) --------------- ------ ------------------------------ --------- --------- --------- 3195.968367 [0003] <idle> 0.000 0.000 0.000 3195.968386 [0002] Timer[4306/4277] 0.000 0.000 0.018 3195.968397 [0002] Web Content[4277] 0.000 0.000 0.000 3195.968595 [0001] JS Helper[4302/4277] 0.000 0.000 0.000 3195.969217 [0000] <idle> 0.000 0.000 0.621 3195.969251 [0001] kworker/1:1H[291] 0.000 0.000 0.033 The sample starts at 3195.968367 but when I gave a time interval from 3194 to 3196 (in sec) it will calculate the whole 2 second as runtime. In below, 2 cpus accounted it as runtime, other 2 cpus accounted it as idle time. Before: $ perf sched timehist --time 3194,3196 -s | tail Idle stats: CPU 0 idle for 1995.991 msec CPU 1 idle for 20.793 msec CPU 2 idle for 30.191 msec CPU 3 idle for 1999.852 msec Total number of unique tasks: 23 Total number of context switches: 128 Total run time (msec): 3724.940 After: $ perf sched timehist --time 3194,3196 -s | tail Idle stats: CPU 0 idle for 10.811 msec CPU 1 idle for 20.793 msec CPU 2 idle for 30.191 msec CPU 3 idle for 18.337 msec Total number of unique tasks: 23 Total number of context switches: 128 Total run time (msec): 18.139 Cc: David Ahern <dsah...@gmail.com> Fixes: 853b74071110 ("perf sched timehist: Add option to specify time window of interest") Signed-off-by: Namhyung Kim <namhy...@kernel.org> --- tools/perf/builtin-sched.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c index 5052caa91caa..d53e706a6f17 100644 --- a/tools/perf/builtin-sched.c +++ b/tools/perf/builtin-sched.c @@ -2405,7 +2405,7 @@ static int timehist_sched_change_event(struct perf_tool *tool, if (ptime->start && ptime->start > t) goto out; - if (ptime->start > tprev) + if (tprev && ptime->start > tprev) tprev = ptime->start; /* -- 2.10.0