Re: [PATCH tip/core/rcu 04/26] rcu: Settle config for userspace extended quiescent state

Frederic Weisbecker
2012-09-10T21:35:28Z

On Tue, Sep 04, 2012 at 05:46:19PM -0700, Josh Triplett wrote:
> > It actually does depend on SMP. There has to be at least one CPU taking
> > scheduling-clock interrupts in order to keep time computation accurate,
> > so a de-facto UP system cannot adaptive-dynticks its sole CPU.
>
> Ah. That seems like a removable limitation, albeit a difficult one.
> Nonetheless, it makes sense to avoid providing the option when it won't
> help.
>
> However, once a config symbol for adaptive dynticks exists, perhaps that
> symbol should depend on SMP and RCU_USER_QS should depend on that
> instead, documenting the limitation in the right place and making it
> easier to find and change eventually.

Right! And in fact CONFIG_RCU_USER_QS is a temporary config. Once we'll have
CONFIG_NO_HZ_FULL, we won't need intermediate configs like this.
And CONFIG_NO_HZ_FULL will depend on SMP anyway.