[LTP] [PATCH v2] sched: starvation: Autocallibrate the timeout

[joe.liu]

> Hi!
> > > Instead of hardcoding the values we attempt to measure the CPU speed and
> > > set the timeout accordingly. Given that the difference in the duration
> > > of the test when the kernel is buggy is about 30x we do not have to have
> > > a precise callibration, just very rough estimate if we are running on a
> > > server or small ARM board would suffice.

> > > So we attempt to measure how long does a bussy loop take and base the
> > > default timeout on that. On x86_64 CPUs the resulting timeout is about
> > > double of the value of the actual test runtime and works fine, but we
> > > need to make sure that the coeficient we divide the result from
> > > callibrate works for small boards too. So please run the test on as many
> > > machines as you can and report if we need to make the dividor smaller or
> > > not.
 
> > While applying this new patch, the test result of 32bit kernel is still failed. Please refers following log:
> > 
> > external/ltp/lib/tst_test.c:1690: TINFO: LTP version: 20230929
> > external/ltp/lib/tst_test.c:1576: TINFO: Timeout per run is 0h 00m 30s
> > external/ltp/testcases/kernel/sched/cfs-scheduler/starvation.c:90: TPASS: sched_setaffinity(0, sizeof(mask), &mask) returned 0
> > external/ltp/testcases/kernel/sched/cfs-scheduler/starvation.c:58: TINFO: CPU did 100000000 loops in 198306us
> > external/ltp/testcases/kernel/sched/cfs-scheduler/starvation.c:99: TINFO: cal timeout: 198
> > external/ltp/lib/tst_test.c:1583: TINFO: Updating max runtime to 0h 03m 18s
> > external/ltp/lib/tst_test.c:1576: TINFO: Timeout per run is 0h 03m 48s
> > Test timeouted, sending SIGKILL!
> > 
> > After using "time ./starvation" to check the timecost, we can see the timecost is about 26 mins and 48 seconds

> This is really strange. I tested the code on RPi Zero with 32bit BCM2835
> where the CPU is even slower and runtime limit is set to about 5
> minutes, yet the test finished in a minute. That's with resonably recent
> kernel 6.1 though.

> What kernel version do you use?
We are now using kernel 5.15

> Do you run LTP with background tasks to keep the CPU bussy?
Yes, we are testing LTP with Android VTS. And the test environment is under Android Launcher.

> Do you have any custom patches for kernel scheduller applied?
I think there is no any patch applied for kernel scheduller.

> It really looks like something unexpected is happening at your end.

Actually, the same kernel version using 64bit kernel can pass the ltp test.



1. for 32bit kernel, we have this log

32bit kernel
external/ltp/testcases/kernel/sched/cfs-scheduler/starvation.c:161: TINFO: do_test by pid 4523
external/ltp/testcases/kernel/sched/cfs-scheduler/starvation.c:166: TINFO: main pid is 4523
external/ltp/testcases/kernel/sched/cfs-scheduler/starvation.c:167: TINFO: child pid is 4524
external/ltp/testcases/kernel/sched/cfs-scheduler/starvation.c:166: TINFO: main pid is 4524
external/ltp/testcases/kernel/sched/cfs-scheduler/starvation.c:167: TINFO: child pid is 0
external/ltp/testcases/kernel/sched/cfs-scheduler/starvation.c:176: TINFO: go loop, current pid is 4523
external/ltp/testcases/kernel/sched/cfs-scheduler/starvation.c:145: TINFO: current ppid is 4523, current pid is 4524, go to child() start

main pid is 4523, child pid is 4524, and we only see child pid is working (checking by top)

4524 root         20   0  14M 472K    0 R 85.7   0.0   0:14.93 starvation_v4 -t 1000000 -l 1000000 <-- cpu_load by top




2. for 64bit kernel, we have this log

64bit kernel
external/ltp/testcases/kernel/sched/cfs-scheduler/starvation.c:161: TINFO: do_test by pid 9753
external/ltp/testcases/kernel/sched/cfs-scheduler/starvation.c:166: TINFO: main pid is 9753
external/ltp/testcases/kernel/sched/cfs-scheduler/starvation.c:167: TINFO: child pid is 9754
external/ltp/testcases/kernel/sched/cfs-scheduler/starvation.c:166: TINFO: main pid is 9754
external/ltp/testcases/kernel/sched/cfs-scheduler/starvation.c:167: TINFO: child pid is 0
external/ltp/testcases/kernel/sched/cfs-scheduler/starvation.c:176: TINFO: go loop, current pid is 9753
external/ltp/testcases/kernel/sched/cfs-scheduler/starvation.c:145: TINFO: current ppid is 9753, current pid is 9754, go to child() start

main pid is 9753, child pid is 9754, and we see both main and child pid are working (checking by top)

9754 root         20   0  16M 472K    0 R 51.4   0.0   0:05.51 starvation_v4 -t 1000000 -l 1000000 <-- cpu_load by top
9753 root         20   0  16M 464K    0 R 45.7   0.0   0:05.70 starvation_v4 -t 1000000 -l 1000000 <-- cpu_load by top