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 <jack@xxxxxxxx> SUSE Labs, CR
