linux-kernel - Re: RCU Kconfig help text

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Message-ID: <20090906062441.GD1431@ucw.cz>
Date:	Sun, 6 Sep 2009 08:24:41 +0200
From:	Pavel Machek <pavel@....cz>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Valdis.Kletnieks@...edu, Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: RCU Kconfig help text

On Sat 2009-09-05 13:01:46, Paul E. McKenney wrote:
> On Sat, Sep 05, 2009 at 09:27:10AM -0400, Valdis.Kletnieks@...edu wrote:
> > init/Kconfig says:
> > 
> > "choice
> >         prompt "RCU Implementation"
> >         default TREE_RCU
> > 
> > config TREE_RCU
> >         bool "Tree-based hierarchical RCU"
> >         help
> >           This option selects the RCU implementation that is
> >           designed for very large SMP system with hundreds or
> >           thousands of CPUs.  It also scales down nicely to
> >           smaller systems.
> > 
> > config TREE_PREEMPT_RCU
> >         bool "Preemptable tree-based hierarchical RCU"
> >         depends on PREEMPT
> >         help
> >           This option selects the RCU implementation that is
> >           designed for very large SMP systems with hundreds or
> >           thousands of CPUs, but for which real-time response
> >           is also required.
> > 
> > endchoice"
> > 
> > This leaves somebody who has a laptop wondering which choice is best for
> > a system with only one or two cores that has CONFIG_PREEMPT defined. One
> > choice says it scales down nicely, the other explicitly has a 'depends on
> > PREEMPT' attached to it...
> > 
> > (Yes, I realize in practice, the RCU sections on a laptop are probably usually
> > so short they don't matter in practice.  I finally concluded TREE_PREEMPT was
> > apparently a rename of CONFIG_PREEMPT_RCU and went with that since that was
> > working for me before...)
> 
> Good point -- I will add the "It also scales down nicely to smaller
> systems" to TREE_PREEMPT_RCU.
> 
> For -really- small systems, TINY_RCU will hopefully be there at some
> point, but it can only handle single-CPU systems.

If so, call it 'UP_RCU' or 'UNIPROCESSOR_RCU'?
								Pavel

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