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

From: Ingo Molnar
Date: Tue Nov 09 2004 - 17:27:03 EST

* Mark_H_Johnson@xxxxxxxxxxxx <Mark_H_Johnson@xxxxxxxxxxxx> wrote:

> >i have released the -V0.7.23 Real-Time Preemption patch, which can be
> >downloaded from the usual place:
> >
> >
> A few notes on results from running with this patch (well, actually
> -EA that Ingo provided separately).
> [1] Build problems, separately reported to Ingo with CONFIG_PREEMPT_RT
> enabled on x86 and you have modules using kunmap_atomic. Fix by adding
> kunmap_virt and kmap_to_page to the list of exports.

these should be fixed in -V0.7.24 which i uploaded shortly after
-V0.7.23, based on your reports. In any case, the export problems
trigger with CONFIG_HIGHMEM and the affected subsystems compiled as

> [2] The live lock that I was having seems to have been killed based on
> an hour of testing (I could usually cause it in 5 minutes or less).


> [4] Application level latencies are OK but not great.
> X test - only 90% of CPU loops are within 100 usec of nominal value.
> In previous RT kernels I got > 99% with 100 usec.

this might be a side-effect of the chrt-ing of events/[0|1] and/or
ksoftirqd (which we did to debug the 'freeze' problems) - are those
still chrt-ed? Please review and double-check all SCHED_FIFO tasks in
the system and keep only those that are absolutely necessary for
latencytest's operation [i.e. the soundcard IRQ and latencytest itself]
- everything else should be SCHED_OTHER. Do latencies get any better if
you do this?

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