Messages in this thread | | | Date | Tue, 24 Sep 2013 19:06:31 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH] hotplug: Optimize {get,put}_online_cpus() |
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On 09/24, Steven Rostedt wrote: > > On Tue, 24 Sep 2013 18:03:59 +0200 > Oleg Nesterov <oleg@redhat.com> wrote: > > > On 09/24, Peter Zijlstra wrote: > > > > > > +static inline void get_online_cpus(void) > > > +{ > > > + might_sleep(); > > > + > > > + if (current->cpuhp_ref++) { > > > + barrier(); > > > + return; > > > > I don't undestand this barrier()... we are going to return if we already > > hold the lock, do we really need it? > > I'm confused too. Unless gcc moves this after the release, but the > release uses preempt_disable() which is its own barrier. > > If anything, it requires a comment.
And I am still confused even after emails from Paul and Peter...
If gcc can actually do something wrong, then I suspect this barrier() should be unconditional.
Oleg.
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