Real-Time Preemption, -RT-2.6.10-rc2-mm3-V0.7.32-15

* Ingo Molnar <mingo@elte.hu> wrote:

> this smells too. [...]

found two brown-paperbag bugs that caused bad latencies in the -RT
kernel: when i added PREEMPT_DIRECT (which first showed up in -32-10) i
also added a missed-reschedule bug to try_to_wake_up() and to
mutex/semaphore-unlock (__up()). Oops.

i dont think this bug could explain a msec-range latency because the
syscall return path should catch the missed reschedule and it would need
continuous syscall execution in the milliseconds range by a lowprio task
for a latency to be transported to latencytest, but certainly the bug
doesnt help latencies. The -32-15 kernel can be downloaded from the
usual place:

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

other changes in -32-15: more work on the tracer, cleaner trace output
and the tracing of syscall entries and returns, with arguments and
return values displayed as well (i.e. a simple strace variant). Here is
how a syscall now looks like in /proc/latency_trace:

 loop-tes-3885  0....  100µs > sys_getppid (002fcffc 00000001 0000007b)
 loop-tes-3885  0....  101µs+: sys_getppid (sysenter_past_esp)
 loop-tes-3885  0d...  103µs < (3868)

'< (return-val)' is the syscall return value, '> sys_name(params)' is
the syscall itself. (note that the return path is also used by
interrupts, so it's not purely a syscall-return point) This makes it
easier to track userspace execution.

	Ingo
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