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

Peter Zijlstra
2013-11-22T11:33:12Z

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.

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