Re: CPU Hotplug rework

[Rusty Russell]

On Thu, 22 Mar 2012 15:49:20 -0700, "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx> wrote:
> On Thu, Mar 22, 2012 at 02:55:04PM +1030, Rusty Russell wrote:
> > On Wed, 21 Mar 2012 10:01:59 +0100, Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> wrote:
> > > Thing is, if its really too much for some people, they can orchestrate
> > > it such that its not. Just move everybody in a cpuset, clear the to be
> > > offlined cpu from the cpuset's mask -- this will migrate everybody away.
> > > Then hotplug will find an empty runqueue and its fast, no?
> > 
> > I like this solution better.
> 
> As long as we have some way to handle kthreads that are algorithmically
> tied to a given CPU.  There are coding conventions to handle this, for
> example, do everything with preemption disabled and just after each
> preempt_disable() verify that you are in fact running on the correct
> CPU, but it is easy to imagine improvements.

I don't think we should move per-cpu kthreads at all.  Let's stop trying
to save a few bytes of memory, and just leave them frozen.  They'll run
again if/when the CPU returns.

Cheers,
Rusty.
-- 
  How could I marry someone with more hair than me?  http://baldalex.org
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