Re: 3.12.6-rt9 on AM335x (armv7)

[Matthias Fuchs <mfuchs@ma-fu.de>]

Hi Tim,

without hackbench and frieds (idle system) I get a max. latency of about 4ms.
Running hackbench (default arguments, -l 1000), it  still increases up to 5ms:

...
# Total: 000000193
# Min Latencies: 00024
# Avg Latencies: 00205
# Max Latencies: 05058
...

The obvious PM stuff is disabled. No dynamic frequency scaling, etc.
Really weired stuff. I already mentioned the 3.2 system with the same CPU in the OSADL
lab. It comes with max. latency of 118us. So I really expect something similiar.

Matthias

On 01/07/2014 09:38 AM, Tim Sander wrote:
> Hi
>> after some chatting with Nicholas and being sure that I didn't do anything
>> totally stupid I would like to provide my current kernel config and a trace
>> generated by "cyclictest ... -b500".
>>
>> kernel config -> https://www.dropbox.com/s/zsud0b77xoosjm1/config
>> trace ->
>> https://www.dropbox.com/s/5uf58oqo0qwcn4x/trace-cyclictest-2508us.txt
>>
>> I still get max latencies of about 4000us on this TI AM335x system running
>> 3.12.6-rt9 with timers-do-not-raise-softirq-unconditionally.patch reverse
>> applied.
>>
>> sched_rt_runtime_us and sched_rt_period_us are identical. The system is idle
>> during the test. Rootfilesystem comes via NFS.
>>
>> root@generic-armv7a:~# cat /proc/sys/kernel/sched_rt_runtime_us
>> 1000000
>> root@generic-armv7a:~# cat /proc/sys/kernel/sched_rt_period_us
>> 1000000
>>
>> root@generic-armv7a:~# uname -a
>> Linux generic-armv7a 3.12.6-rt9-dirty #3 SMP PREEMPT RT Sat Jan 4 23:01:19
>> CET 2014 armv7l GNU/Linux
>>
>> root@generic-armv7a:~# ~/cyclictest -p99 -m -n -i200 -h400 -q -l100000 -b
>> 500 # /dev/cpu_dma_latency set to 0us
>> INFO: debugfs mountpoint: /sys/kernel/debug/tracing/
>> could not set ftrace_enabled to 0
>> could not set tracing_max_latency to 0
>> # Histogram
>> ...
>> # Total: 000018604
>> # Min Latencies: 00024
>> # Avg Latencies: 00158
>> # Max Latencies: 02508
> Wohaa, thats bad for a latency patched kernel. Have you disabled 
> powermanagement? I have an older rt patched kernel and it was not too good.
> If i remember correctly it was between 100-200µs latency. But thats
> far better than this. You could also load the system with hackbench, if its 
> the idle pm than latency would get better.
> 
> Best regards
> Tim
> 
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