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Subject[patch] Real-Time Preemption, -RT-2.6.10-rc1-mm3-V0.7.23

i have released the -V0.7.23 Real-Time Preemption patch, which can be
downloaded from the usual place:

this release includes fixes, development/debugging improvements and
latency improvements and other speedups.

the biggest change is the reworked timing/tracing framework. Wakeup
timing became a compile-time thing and can be selected independently of
the preemption mode - i.e. it can now be used on near-vanilla !PREEMPT
kernels too, providing good wakeup-latency comparison of the various
preemption models.

irqs-off and preempt-off critical section timing/tracing can be selected
if wakeup timing is disabled, the two options can be selected separately
or together as well.

another improvement is that wakeup-timing now works correctly on SMP too
- the tracer 'follows' the highest-priority task in the system as it
gets bounced between CPUs and always traces the CPU where the task is

other changes since -V0.7.22:

- semaphore livelock fix: feedback from Mark H. Johnson pinpointed a
bug in the down_trylock() semaphore code: if preempted in the wrong
moment a lower-prio task could cause a higher-prio task to livelock
indefinitely. This fix could solve the 'keventd looping' problem
reported by Mark.

the fix is to make the down_trylock() code a bit simpler, but this
also introduces the potential for down_trylock() to get 'spurious'
locking-rejects. Hopefully this wont be a big problem - we dont
really guarantee that down_trylock() succeeds - but code using higher
semaphore counts to track resources could be negatively impacted by
this. We'll see.

- console assert fix: implemented a different type of fbcon
RT-preemption handling variant, this could solve the assert reported
by Amit Shah.

- debugging improvement: implemented a sequence counter for max latency
traces. This has the advantage of solving the 'slow console on SMP
problem': the latency-timing code used to get confused by another CPU
printing a timing message to a slow console and thus delaying that
other CPU. Now any latency that gets generated while a maximum is
printed is skipped.

- further shrunk the non-debug size of struct rt_mutex by moving the
save_state logic into the debug paths - size is now 4 machine-words.

- fixed CONFIG_HIGHMEM latencies: all atomic-kmap APIs are now wrapped
seemlessly and in a preemptible way.

- implemented an IO-APIC register cache to speed up the IRQ-redirection
latency hotpath. Also, made the POST flush a bit faster.

- disable KGDB if PREEMPT_RT - it's broken for now.

- move some runtime checks to under DEBUG_PREEMPT - this speeds up

to create a -V0.7.23 tree from scratch, the patching order is:

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