Re: [PATCH -v7][RFC]: mutex: implement adaptive spinning

Peter Zijlstra
2009-01-08T15:31:00Z

On Thu, 2009-01-08 at 10:28 -0500, Steven Rostedt wrote:
> On Thu, 8 Jan 2009, Peter Zijlstra wrote:

> > in the unlikely case we schedule(), that seems expensive enough to want
> > to make the spin case ever so slightly faster.
>
> OK, that makes sense, but I would comment that. Otherwise, it just looks
> like another misuse of the unlikely annotation.

OK, sensible enough.

> > > Should we need to do a "get_cpu" or something? Couldn't the CPU disappear
> > > between these two calls. Or does it do a stop-machine and the preempt
> > > disable will protect us?
> >
> > Did you miss the preempt_disable() a bit up?
>
> No, let me rephrase it better. Does the preempt_disable protect against
> another CPU from going off line? Does taking a CPU off line do a
> stop_machine?

Yes and yes.