Sebastian Andrzej Siewior 3bd3706251 sched/core: Provide a pointer to the valid CPU mask
In commit:

  4b53a3412d66 ("sched/core: Remove the tsk_nr_cpus_allowed() wrapper")

the tsk_nr_cpus_allowed() wrapper was removed. There was not
much difference in !RT but in RT we used this to implement
migrate_disable(). Within a migrate_disable() section the CPU mask is
restricted to single CPU while the "normal" CPU mask remains untouched.

As an alternative implementation Ingo suggested to use:

	struct task_struct {
		const cpumask_t		*cpus_ptr;
		cpumask_t		cpus_mask;
        };
with
	t->cpus_ptr = &t->cpus_mask;

In -RT we then can switch the cpus_ptr to:

	t->cpus_ptr = &cpumask_of(task_cpu(p));

in a migration disabled region. The rules are simple:

 - Code that 'uses' ->cpus_allowed would use the pointer.
 - Code that 'modifies' ->cpus_allowed would use the direct mask.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20190423142636.14347-1-bigeasy@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-06-03 11:49:37 +02:00
..
2018-08-22 10:52:48 -07:00
2018-10-12 09:17:46 +02:00
2019-05-14 19:52:49 -07:00
2018-08-16 12:14:42 -07:00
2018-08-22 10:52:48 -07:00
2019-01-05 13:54:53 -08:00
2019-03-12 10:04:02 -07:00
2017-02-24 17:46:57 -08:00
2018-04-12 09:41:19 -07:00
2018-10-16 13:45:44 +02:00
2018-06-27 18:58:49 +03:00
2018-10-15 16:31:29 -04:00
2019-05-06 11:12:09 -07:00
2017-08-15 09:02:07 -07:00