Hi Peter --
--- In Peter Gammie <> wrote:
>
> Charles:
>
> On 18/01/2010, at 4:20 PM, Charles wrote:
>
> > Any chance you could pass the clockevents patch on to Matthieu to include
> > in his patchset? HRT would help lots of users, I think, even without the
> > -rt support.
>
> No promises, but I could try to do that if anyone else shows an interest. :-)
>
> Are Matthieu's patches hosted anywhere except in the Yahoo file
Sure, they are at http://mcrapet.free.fr/
He's up to 2.6.32.3, but doesn't have HRT yet AFAIK. Search this group archive
for '10ms' to gauge interest, it's come up many times before :)
area? Can he (or someone) tell me what the status wrt the linux mainline is?
I'm not a kernel hacker, but I surmise that RT got merged sometime around
2.6.31, and there seem to be have been a steady stream of ts72xx/ep93xx patches
going in.
Only some of his patches have gone in, and some will never make it (like the
force_machine_id patch). Matt's patchset has never included the preempt-rt
code from
http://www.kernel.org/pub/linux/kernel/projects/rt/
which is now up to 2.6.31.6-rt19.
>
> The 2.6.29.6 kernel I built does sub-10ms delays, dare I say even sub-100ns
> delays using clock_nanosleep, but the RT scheduler (FIFO/highest priority) is
> not keeping up its part of the bargain: running top glitches the multiplexed
> display scanning loop. This loop is only twiddling some GPIO lines in the
> manner of Jim Jackson's ts_arm_util (i.e. reading and writing to the mmap'd
> GPIO addresses) - I can't make it much tighter. The CPU load due to my
> program is something like 0.01% all up.
There are some cool tests here:
http://www.kernel.org/pub/linux//kernel/people/clrkwllms/rt-tests
And a good explanation of how to trace latencies in this thread:
http://marc.info/?l=linux-rt-users&m=126142802114499&w=2
You might have better luck *without* the -rt patch, ironically. That intends
to have deterministic latencies, but not necessarily the lowest. Try just the
normal config-preempt from the vanilla kernel (but with HRT of course). You
don't have the PM stuff enabled in Matt's patches do you? If there's anything
you don't need (USB, ethernet, serial, etc), take it out.
regards, .......... Charlie
>
> I'll try to look into it sometime soon.
>
> cheers
> peter
>
> --
> http://peteg.org/
>
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