On Thu, 6 Apr 2017, Peter Zijlstra wrote:
> On Thu, Apr 06, 2017 at 11:25:42AM +0200, Sebastian Andrzej Siewior wrote:
> > > I.e. just have a counter and these two APIs:
> > >
> > > static inline void migrate_disable(void)
> > > {
> > > current->migration_disabled++;
> > plus
> > if (current->migration_disabled == 1)
> > get_online_cpus()
>
> You want that other hotplug fast hack crap you have in rt, no?
As I said in the other mail, we certainly want to make get_online_cpus()
fast independently of RT. That's on our todo list anyway.
> Because mainline will not get anything other than prempt_disable() for
> migrate_disable().
I'm not yet convinced of that. There is enough stuff which pointlessly
disables preemption and works around the restrictions caused by that or
plays games with cpus_allowed just to stay on a particular cpu.
I know you don't like it because it imposes restrictions on schedulability,
but disabling preemption for a long time or playing cpus_allowed games has
the same and worse effects.
Thanks,
tglx
