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Message-ID: <20120910213506.GC21277@somewhere.redhat.com>
Date: Mon, 10 Sep 2012 23:35:19 +0200
From: Frederic Weisbecker <fweisbec@...il.com>
To: Josh Triplett <josh@...htriplett.org>
Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
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Alessio Igor Bogani <abogani@...nel.org>,
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Sven-Thorsten Dietrich <thebigcorporation@...il.com>
Subject: Re: [PATCH tip/core/rcu 04/26] rcu: Settle config for userspace
extended quiescent state
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.
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