On Wed, Oct 24, 2007 at 10:17:54PM +0400, Oleg Nesterov wrote:
> On 10/24, Gautham R Shenoy wrote:
> >
> > On Wed, Oct 24, 2007 at 10:04:41AM -0700, Christoph Lameter wrote:
> > > On Wed, 24 Oct 2007, Gautham R Shenoy wrote:
> > >
> > > > This is the version 2 of the refcount based cpu-hotplug "locking"
> > > > implementation.
> > >
> > > Uggh. This introduces a global lock that has to be taken always when
> > > scanning over cpus?
> >
> > Well, no! we take the global lock only while bumping up the refcount.
> > We don't hold the lock while scanning over the cpus. And this is
> > definitely an improvement over the lock_cpu_hotplug() global mutex
> > we have now.
>
> Just to be sure I didn't miss something... preempt_disable() still works,
> yes?
Yes it does. But it doesn't prevent onlining of new cpus.
I am checking if __cpu_up() can also be called safely using
stop_machine_run() so that we can use preempt_disable() for safe atomic
access of the cpu_online_map.
>
> Oleg.
>
Thanks and Regards
gautham.
--
Gautham R Shenoy
Linux Technology Center
IBM India.
"Freedom comes with a price tag of responsibility, which is still a bargain,
because Freedom is priceless!"
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