linux-kernel - RCU Kconfig help text

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Date:	Sat, 05 Sep 2009 09:27:10 -0400
From:	Valdis.Kletnieks@...edu
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org
Subject: RCU Kconfig help text

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...)

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