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
