Re: [PATCH 2/4] timer: relax tick stop in idle entry

Jacob Pan
2015-11-16T23:16:00Z

On Mon, 16 Nov 2015 14:31:17 -0800
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:

> > Either one works but my concern is that users may not realize the
> > intricate CONFIG_ options and how they translate into energy
> > savings. Consulted with Josh, it seems we could add a check here to
> > recognize the forced idle state and relax rcu_needs_cpu() to return
> > false even it has callbacks. Since we are blocking everybody for a
> > short time (5 ticks default). It should not impact synchronize and
> > kfree rcu.
>
> Or we could just set things up so that whatever Kconfig you are using
> to enable this state causes CONFIG_RCU_NOCB_CPU_ALL to also be
> enabled. Or that causes CONFIG_RCU_FAST_NO_HZ to also be enabled, if
> that works better for you.
That would be great, we can work this out once the patch is
finalized. This is not a hard dependency in that it only affects the
efficiency of idle injection.