lkml.org 
[lkml]   [2013]   [Sep]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] hotplug: Optimize {get,put}_online_cpus()
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.



\
 
 \ /
  Last update: 2013-09-24 19:21    [W:0.168 / U:0.132 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site