Re: [PATCH 3/7] idle, thermal, acpi: Remove home grown idle implementations

Paul E. McKenney
2013-11-22T17:17:36Z

On Fri, Nov 22, 2013 at 12:33:00PM +0100, Peter Zijlstra wrote:
> On Thu, Nov 21, 2013 at 08:20:36PM -0800, Paul E. McKenney wrote:
> > The 6ms to 25ms range should be just fine as far as normal RCU grace
> > periods are concerned. However, it does mean that expedited grace
> > periods could be delayed: They normally take a few tens of microseconds,
> > but if they were unlucky enough to show up during an idle injection,
> > they would be magnified by two to three orders of magnitude, which is
> > not pretty.
> >
> > Hence my suggestion of hooking into RCU on idle-injection start and end
> > so that RCU considers that time period to be idle. Just like it does
> > for user-mode execution on NO_HZ_FULL kernels, so I still don't see this
> > approach to be a problem. I must confess that I still don't understand
> > what Arjan doesn't like about it.
>
> Using these patches it would indeed use the RCU idle machinery as per
> the normal idle path.

OK, sorry for my confusion!

> If you can I can add more WARN_ON()s in play_idle() to ensure we're not
> called while holding any RCU locks.

An rcu_sleep_check() or something similar, please!

Thanx, Paul