On 15/09/10 17:08, Thomas Gleixner wrote:
On Wed, 15 Sep 2010, Agustin Ferrin Pozuelo wrote:
On 27/08/10 11:35, Thomas Gleixner wrote:
On Mon, 23 Aug 2010, Agustin Ferrin Pozuelo wrote:
Sorry, my test setup is not very comprehensive at the moment. I have some
overnight/overweekend results at hand with millions of loops:
PREEMPT-DESKTOP:
root@at91sam9263cpc:~# time cyclictest -i 70000 -p 80 -h 700 -r
Oh, you are running cyclictest with a signal based timer and relative
time. Any reason for this ?
Not sure about the "signal based timer", is there an alternative to it?
(clock_nanosleep?)
The relative time setting "-r" I put there to prevent issues with some
specific configurations, specially when the interval was smaller than
max latency, in which case cyclictest would freeze or give unusable
results. That was happening often before using the workaround for the
9263 ethernet bug which induced long latencies (non RT at all).
What happens if you change the command line to
cyclictest -i 70000 -p 80 -n
Interesting, "-n" setting (use clock_nanosleep) brings down the min and
avg latencies for 35~40 us. (~70 when using "-r") on the PREEMPT-DESKTOP
configuration:
root@at91sam9263cpc:~# cyclictest -i 70000 -p 80 -l 1000
Clock resolution: 0.000000001 (s.ns)
policy: fifo: loadavg: 0.14 0.13 0.06 1/36 954
T: 0 ( 876) P:80 I:70000 C: 1000 Min: 107 Act: 135 Avg: 164
Max: 262
root@at91sam9263cpc:~# cyclictest -i 70000 -p 80 -l 1000 -n
Clock resolution: 0.000000001 (s.ns)
policy: fifo: loadavg: 0.14 0.12 0.05 1/37 874
T: 0 ( 795) P:80 I:70000 C: 1000 Min: 72 Act: 127 Avg: 125
Max: 275
root@at91sam9263cpc:~# cyclictest -i 70000 -p 80 -l 1000 -r
Clock resolution: 0.000000001 (s.ns)
policy: fifo: loadavg: 0.04 0.10 0.06 1/36 1035
T: 0 ( 956) P:80 I:70000 C: 1000 Min: 145 Act: 205 Avg: 203
Max: 348
root@at91sam9263cpc:~# cyclictest -i 70000 -p 80 -l 1000 -r -n
Clock resolution: 0.000000001 (s.ns)
policy: fifo: loadavg: 0.01 0.07 0.05 2/37 1115
T: 0 ( 1037) P:80 I:70000 C: 1000 Min: 87 Act: 135 Avg: 150
Max: 439
(Longer runs giving similar results)
Note that"-r" seems to lower CPU usage, is loadavg 0.14 == 14% or 0.0014%?
Right now I don't have the PREEMPT-RT version available for this test,
should I expect big improvement there?
I am assuming context switching is more expensive on PREEMPT-RT under ARM9,
where it seems already a bit expensive.
No, the context switch is equally expensive, but signal delivery might
be a bit more overhead on -RT
Thanks for the clarification and tips!
Regards,
--Agustín.
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Agustín Ferrín Pozuelo
Embedded Systems Engineer
CG Power Systems Ireland Limited
Automation Systems Division
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