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Subject[patch] Real-Time Preemption, -RT-2.6.9-mm1-V0

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

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

NOTE: this is a highly experimental release, a more experimental one
than -U10.3.

the big change in the '-V' series of the patchset is that i have
converted the last couple of non-preemptible kernel subsystems to
fully-preemptible mutex-based locking. These subsystems are:

- the SLAB allocator
- the buddy page allocator
- waitqueue handling
- soft-timer subsystem
- security/selinux
- workqueues
- the random driver

this is probably the last 'big leap forward' in terms of the scope of
the patch. (having reached the ultimate scope: it now encompasses
everything ;)

But as an inevitable result of this big leap it will likely break in a
couple of places. Unfortunately these subsystems were largely
interdependent so it's an all-or-nothing step with not much middle
ground between the locking done in -U10.3 and in -V0.

another result of these changes is that the number of critical sections
in -V0 is roughly 30% of that in -U10.3. Now we only have the scheduler
and very lowlevel IRQ-hardware locks as raw spinlocks. (plus the lone
holdout vga_lock - which i will probably make a mutex too in the near
future)

[ NOTE: there's one known bug in this release: selinux on one of my
testsystems broke, it hangs during bootup. With CONFIG_SECURITY disabled
it works fine. I'm working on the fix. So please keep CONFIG_SECURITY
disabled for the time being. ]

other changes in -V0:

- build fixes: more driver fixes from Thomas Gleixner

- crash fix: fixed a bug found by Thomas Gleixner: rwsem runtime
initialization was racy.

- deadlock fix: fixed lockup bug caused by __schedule clearing
PREEMPT_ACTIVE. The need_resched loop is now outside of __schedule().
This might solve lockups/slowdowns reported by some people.

- latency fix: made keventd SCHED_FIFO - this could fix the mouse
related delays reported by a number of people.

- latency fix: fixed SMP lock-break mechanism of mutexes.

- usability feature: hard-interrupts get decreasing SCHED_FIFO priority
starting at prio 49 and stopping at prio 25. This should give a good
default.

- debug feature: implemented SysRq-D to show the list of tasks with
locks blocked on, if RW_SEM_DEADLOCK_DETECTION is enabled.

to create a -V0 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/people/akpm/patches/2.6/2.6.9/2.6.9-mm1/2.6.9-mm1.bz2
+ http://redhat.com/~mingo/realtime-preempt/realtime-preempt-2.6.9-mm1-V0

Ingo
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