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SubjectPPC RT Patch..
Ingo,
We've had a PPC port of your RT work underway with
a focus on trace instrumentation. This is based upon
realtime-preempt-2.6.11-rc2-V0.7.37-02. A diff is
attached.

To the extent possible the tracing facilities are the
same as your x86 work. In the process a few PPC/gcc
issues needed to be resolved. There is also a bug fix
contained for tlb_gather_mmu() which was causing debug
assertions to be generated in a path which attempted to
sleep with a non-zero preempt count.

This does build and function when SMP is configured,
though we have not yet verified it on other than a
uniprocessor. As a simplifying assumption, testing has
thus far concentrated on the following modes:

PREEMPT_NONE
- verify baseline regression

PREEMPT_RT && !PREEMPT_SMP
- typical for an embedded RT PPC application

PREEMPT_RT && PREEMPT_SMP
- kicks in live locking code which otherwise receives no
coverage. This is functionally equivalent to the above
config on a single CPU target thus no MP dynamic testing
is achieved. Still quite useful IMHO.

The target used for development/testing is an Ampro EnCore PP1
which sports a 300Mhz MPC8245. For testing this boots with NFS
as root. An mp3 decode at nice --20 is launched which requires
just under 20% of the CPU to maintain an uninterrupted audio
decode and output. To this a series of "du -s /" are launched
to soak up excess CPU bandwidth. Perhaps not rigorous but a
fair sanity check and load for the purpose at hand.

Under these conditions maximum scheduling latencies are seen in
the 120-150us range. Note no attempt has yet been made to
optimize arch specific paths and full trace instrumentation has
been enabled.

I've written some logging code to help find problems such as
the tlb issue above. As it has not been made general I've
removed it from this patch. At some point I'll likely revisit
this.

Comments/suggestions welcome.

-john


--
john.cooper@timesys.com
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