On Fri 18-09-20 15:09:14, Oleg Nesterov wrote:
> On 09/18, Peter Zijlstra wrote:
> > > But again, do we really want this?
> >
> > I like the two counters better, avoids atomics entirely, some archs
> > hare horridly expensive atomics (*cough* power *cough*).
>
> I meant... do we really want to introduce percpu_up_read_irqsafe() ?
>
> Perhaps we can live with the fix from Hou? At least until we find a
> "real" performance regression.
I can say that for users of percpu rwsem in filesystems the cost of atomic
inc/dec is unlikely to matter. The lock hold times there are long enough
that it would be just lost in the noise.
For other stuff using them like get_online_cpus() or get_online_mems() I'm
not so sure...
Honza
--
Jan Kara <[email protected]>
SUSE Labs, CR
