Dear all.
We have an embedded board based on Freescale imx25 (ARM9 at 400 MHz)
with 64MB RAM and Linux 2.6.31 provided by Freescale.
We have ported PREEMPT_RT-21 and made some measurements using the
rt-tests suite (cloned from the official repo at
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git).
Summing up, our reference software is
Architecture: imx25
Kernel: 2.6.31 provided by Freescale
Preempt_Rt patch: rt21
TestSuite: rt-tests V0.84
The cyclictest showed a reduction of the maximum latency, as we were
expecting.
However, the other tests showed a maximum latency higher than without
the patch (which is supposed to reduce the maximum latency).
Please, find below the results that we have obtained.
We know that this version of preempt_rt is outdated. However, we can't
figure out how the maximum latency can be higher.
Do you have any idea about the possible reason of this behavior ?
Many thanks,
Claudio and Alessandro
SIGNALTEST:
Without preempt_rt:
$ signaltest -l 10000 -t 4
0.40 0.92 0.58 1/35 2199
T: 0 ( 2196) P: 0 C: 10000 Min: 157 Act: 184 Avg: 219 Max:
1246
With preempt_rt:
$ signaltest -l 10000 -t 4
0.03 2.87 6.53 3/62 2684
T: 0 ( 2681) P: 0 C: 10000 Min: 215 Act: 260 Avg: 384 Max:
2038
SIGWAITTEST:
Without preempt_rt:
$ sigwaittest -l 10000 -t 2
#0: ID2201, P0, CPU0, I1000; #1: ID2202, P0, CPU0, Cycles 10000
#2: ID2203, P0, CPU0, I1500; #3: ID2204, P0, CPU0, Cycles 7019
#1 -> #0, Min 40, Cur 58, Avg 71, Max 1191
#3 -> #2, Min 42, Cur 61, Avg 69, Max 954
With preempt_rt:
$ sigwaittest -l 10000 -t 2
#0: ID2687, P0, CPU0, I1000; #1: ID2688, P0, CPU0, Cycles 10000
#2: ID2689, P0, CPU0, I1500; #3: ID2690, P0, CPU0, Cycles 7007
#1 -> #0, Min 51, Cur 63, Avg 105, Max 1379
#3 -> #2, Min 57, Cur 63, Avg 105, Max 2081
SVSEMATEST:
Without preempt_rt:
$ svsematest -l 10000 -t 2
#0: ID2206, P0, CPU0, I1000; #1: ID2207, P0, CPU0, Cycles 10000
#2: ID2208, P0, CPU0, I1500; #3: ID2209, P0, CPU0, Cycles 7094
#1 -> #0, Min 17, Cur 34, Avg 37, Max 940
#3 -> #2, Min 18, Cur 32, Avg 34, Max 809
With preempt_rt:
$ svsematest -l 10000 -t 2
#0: ID2703, P0, CPU0, I1000; #1: ID2704, P0, CPU0, Cycles 10000
#2: ID2705, P0, CPU0, I1500; #3: ID2706, P0, CPU0, Cycles 6858
#1 -> #0, Min 29, Cur 47, Avg 65, Max 1423
#3 -> #2, Min 30, Cur 91, Avg 83, Max 1314
PI_STRESS:
Finally, the pi_stress (priority-inheritance code paths for POSIX
mutexes) sometimes fails with preempt_rt on the SCHED_FIFO policy (this
behavior did not occurred without preempt_rt, even if it is still possible):
$ pi_stress --duration 100 --groups=2
Starting PI Stress Test
Number of thread groups: 2
Duration of test run: 100 seconds
Number of inversions per group: unlimited
Test threads using scheduler policy: SCHED_FIFO
Admin thread priority: 4
2 groups of 3 threads will be created
High thread priority: 3
Med thread priority: 2
Low thread priority: 1
Current Inversions: 2531
ERROR: WATCHDOG triggered: group 0 is deadlocked!
ERROR: reporter stopping due to watchdog event
Stopping test
Terminated
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