Re: cpufreq + PREEMPT_RT_FULL give bad context sleeping BUG

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

* Gregoire Gentil | 2013-03-27 08:23:16 [-0700]:

>>>>[0] http://dev.omapzoom.org/?p=integration/kernel-ubuntu.git;a=blob;f=arch/arm/plat-omap/clock.c;h=8c0e8fe2c5c51673e41e4304194d922dbfaedf38;hb=3e1c9f139425663ceee48f92e8d3f23158580334
>>>
>>>Yeah, it's that way in mainline as well.
>>
>>I meant, that the mutex is taken. So yes, this will cause a warning in
>>!RT too.
>Hello,
>
>So what could be a tentative solution? Could you advise what I could try?

The easy way would be to get the clockfw_lock lock changed into a
raw_spinlock_t and fix clk_get_rate() and others. If the lock is taken
for a long time it will increase you latency.
You try to check if it is possible to defer twd_update_frequency() to a
workqueue and execute it later and not directly from the interrupt.

On the other hand you might want simply disable cpufreq. If you have a
certain latency and the cpu frequency goes down because the system is
idle then you latency will increase. Basicaly an idle machine will worse
latency than a busy one. You probably don't want this.

>
>Many thanks in advance,
>
>Grégoire

Sebastian
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