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Date: Mon, 10 Sep 2012 23:35:19 +0200
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Josh Triplett <josh@joshtriplett.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
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Subject: Re: [PATCH tip/core/rcu 04/26] rcu: Settle config for userspace
 extended quiescent state
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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.