Re: [PATCH 0/6] Optimize the cpu hotplug locking -v2

[Andrew Morton]

On Thu, 10 Oct 2013 12:36:31 -0400 Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> On Thu, 10 Oct 2013 09:00:44 -0700
> Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> 
> > It's been ages since I looked at this stuff :( Although it isn't used
> > much, memory hotplug manages to use stop_machine() on the add/remove
> > (ie, "writer") side and nothing at all on the "reader" side.  Is there
> > anything which fundamentally prevents cpu hotplug from doing the same?
> 
> 
> I would think that memory hotplug may require stop machine as all CPUs
> may touch that memory.

Sure.

> But we would like to remove stomp machine from
> CPU hotplug.

We do?  That's news.  It wasn't mentioned in the changelog and should
have been.  Why?  

> Why prevent all CPUs from running when we want to remove
> one?

So get_online_cpus() goes away.  Nothing is more scalable than nothing!
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