Re: [patch] Real-Time Preemption, -RT-2.6.10-rc2-mm3-V0.7.32-6

From: Mark_H_Johnson
Date: Thu Dec 09 2004 - 14:32:21 EST

>* Mark_H_Johnson@xxxxxxxxxxxx <Mark_H_Johnson@xxxxxxxxxxxx> wrote:
>> >also, i'd like to take a look at latency traces, if you have them for
>> >this run.
>> I could if I had any. The _RT run had NO latency traces > 250 usec
>> (the limit I had set for the test). The equivalent _PK run had 37 of
>> those traces. I can rerun the test with a smaller limit to get some if
>> it is really important. My build of -12 is almost done and we can see
>> what kind of repeatability / results from the all_cpus trace shows.
>/me is puzzled.
>so all the CPU-loop delays within the -RT kernel are below 250 usecs? I
>guess i dont understand what this means then:

There were no cases where /proc/sys/kernel/preempt_max_latency went
over 250 usec in the RT stress test that I did (for the same test, _PK
had over 30 such traces).

>| The max CPU latencies in RT are worse than PK as well. The values for
>| RT range from 3.00 msec to 5.43 msec and on PK range from 1.45 msec to
>| 2.24 msec.
>these come from userspace timestamping? So where userspace detects a
>delay the kernel tracer doesnt measure any?
Yes. That is correct. Very puzzling to me too.

--Mark H Johnson

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