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

[Ingo Molnar <mingo@elte.hu>]

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

    http://redhat.com/~mingo/realtime-preempt/

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
pending.

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 
   CRITICAL_PREEMPT_TIMING.

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

   http://kernel.org/pub/linux/kernel/v2.6/linux-2.6.9.tar.bz2
   http://kernel.org/pub/linux/kernel/v2.6/testing/patch-2.6.10-rc1.bz2
   http://kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.10-rc1/2.6.10-rc1-mm3/2.6.10-rc1-mm3.bz2
   http://redhat.com/~mingo/realtime-preempt/realtime-preempt-2.6.10-rc1-mm3-V0.7.23

	Ingo