Messages in this thread | | | Date | Fri, 18 Sep 2020 15:26:35 +0200 | From | Jan Kara <> | Subject | Re: [RFC PATCH] locking/percpu-rwsem: use this_cpu_{inc|dec}() for read_count |
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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@suse.com> SUSE Labs, CR
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