On Sep 12, 2012, at 3:20 AM, Hartmut Behrens [off-list ref] wrote:

Hi,

I have patched a 3.2 kernel for a OMAP compatible processor (ARM
Cortex A8) to be used on an Gumstix Overo with the CONFIG_PREEMPT_RT
patch.

I have noticed that the latency of the patched kernel on this platform
is <300usec (using cyclictest), similar to what is reported for the
ARM9 platforms at
https://rt.wiki.kernel.org/index.php/CONFIG_PREEMPT_RT_Patch

Is this the best performance that can be expected from ARM7/9 platforms?

Could it be improved by using different kernel config settings - e.g.
CONFIG_LATENCY_TRACE=n  -
https://rt.wiki.kernel.org/index.php/Cyclictest mentions that latency
tracing adds significant kernel overhead?

There are a lot of options that can be eliminated / optimized to reduce memory footprint and overhead.

If you are not using large scale SMP features, things like cgroups, name spaces and so on may shave a few nanoseconds here and there, and that adds up.

You'll have to experiment with the configs, but for typical embedded, less is more.

Historically, if you can run a UP configured Kernel, that tends to be much more lightweight.

The OSADL configs Carsten referenced in separate email are certainly a good starting point.

If you find compile errors as you twiddle with options, please do send the relevant snippets to this list.

Thanks

Sven

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