On Mon, Sep 12, 2016 at 08:20:16PM -0400, Francis Giraldeau wrote:

The args are valid, but the system has an unstable clock, therefore the
operation is not supported. In the user point of view, maybe ENOTSUPP
would be more appropriate? But then, we need to check the reason and
can_stop_my_full_tick() returns only a boolean.

On a side note, the NOSIG mode may be confusing for the users. At first,
I was expecting that NOSIG behaves the same way as the normal task isolation
mode. In the current situation, if the user wants the normal behavior, but
does not care about the signal, the user must register an empty signal handler.

However, if I understand correctly, other settings beside NOHZ and isolcpus
are required to support quiet CPUs, such as irq_affinity and rcu_nocb. It would
be very convenient from the user point of view if these other settings were configure
correctly.

I can work on that and also write some doc (Documentation/task-isolation.txt ?).

That would be lovely! Part of this documentation already exists in
Documentation/timers/NO_HZ.txt and also in Documentation/kernel-per-CPU-kthreads.txt

I think we should extract the isolation informations that aren't related to the tick
from NO_HZ.txt and put them in task-isolation.txt, perhaps merge kernel-per-CPU-kthreads.txt
into it or at least add a pointer to it. Then add all the missing informations as many things
have evolved since then.

I'll gladly help.

Thanks.