linux-kernel - Re: rcu: Provide compile-time control for no-CBs CPUs

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Message-ID: <20130430214919.GL3780@linux.vnet.ibm.com>
Date:	Tue, 30 Apr 2013 14:49:19 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	"Yann E. MORIN" <yann.morin.1998@...e.fr>
Cc:	Dave Jones <davej@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	paul.mckenney@...aro.org, mmarek@...e.cz,
	linux-kbuild@...r.kernel.org
Subject: Re: rcu: Provide compile-time control for no-CBs CPUs

On Tue, Apr 30, 2013 at 11:38:31PM +0200, Yann E. MORIN wrote:
> Paul, Dave, All,
> 
> On Tue, Apr 30, 2013 at 12:25:41PM -0700, Paul E. McKenney wrote:
> > On Tue, Apr 30, 2013 at 02:46:12PM -0400, Dave Jones wrote:
> > > On Tue, Apr 30, 2013 at 03:21:26PM +0000, Linux Kernel wrote:
> > > 
> > >  > +choice
> > >  > +	prompt "Build-forced no-CBs CPUs"
> > >  > +	default RCU_NOCB_CPU_NONE
> > >  > +	help
> > >  > +	  This option allows no-CBs CPUs to be specified at build time.
> > >  > +	  Additional no-CBs CPUs may be specified by the rcu_nocbs=
> > >  > +	  boot parameter.
> > >  > +
> > >  > +config RCU_NOCB_CPU_NONE
> > >  > +	bool "No build_forced no-CBs CPUs"
> > >  > +	depends on RCU_NOCB_CPU
> > >  > +	help
> > >  > +	  This option does not force any of the CPUs to be no-CBs CPUs.
> > >  > +	  Only CPUs designated by the rcu_nocbs= boot parameter will be
> > >  > +	  no-CBs CPUs.
> > >  > +
> > >  > +config RCU_NOCB_CPU_ZERO
> > >  > +	bool "CPU 0 is a build_forced no-CBs CPU"
> > >  > +	depends on RCU_NOCB_CPU
> > >  > +	help
> > >  > +	  This option forces CPU 0 to be a no-CBs CPU.  Additional CPUs
> > >  > +	  may be designated as no-CBs CPUs using the rcu_nocbs= boot
> > >  > +	  parameter will be no-CBs CPUs.
> > >  > +
> > >  > +	  Select this if CPU 0 needs to be a no-CBs CPU for real-time
> > >  > +	  or energy-efficiency reasons.
> > >  > +
> > >  > +config RCU_NOCB_CPU_ALL
> > >  > +	bool "All CPUs are build_forced no-CBs CPUs"
> > >  > +	depends on RCU_NOCB_CPU
> > >  > +	help
> > >  > +	  This option forces all CPUs to be no-CBs CPUs.  The rcu_nocbs=
> > >  > +	  boot parameter will be ignored.
> > >  > +
> > >  > +	  Select this if all CPUs need to be no-CBs CPUs for real-time
> > >  > +	  or energy-efficiency reasons.
> > > 
> > > Note that entering '?' when prompted in oldconfig only outputs the help
> > > parameter from the choice section.
> > 
> > I must defer to the Kconfig experts on this issue.  I have added them on CC.
> 
> Yes. plain '?' will give you the help of the 'choice' menu itself.
> 
> You can get the help entry for each option independently, by entering
> the index followed by a '?', eg. (built-up with copy-paste from above,
> actual display may vary slightly):
> 
>     Build-forced no-CBs CPUs
>     > 1. No build_forced no-CBs CPUs (RCU_NOCB_CPU_NONE) (NEW)
>       2. CPU 0 is a build_forced no-CBs CPU (RCU_NOCB_CPU_ZERO) (NEW)
>       3. All CPUs are build_forced no-CBs CPUs (RCU_NOCB_CPU_ALL) (NEW)
>     choice[1-3?]: 1?
> 
>     RCU_NOCB_CPU_NONE:
> 
>     This option does not force any of the CPUs to be no-CBs CPUs.
>     Only CPUs designated by the rcu_nocbs= boot parameter will be
>     no-CBs CPUs.
> 
>     Symbol: RCU_NOCB_CPU_NONE (=y)
>     Type  : boolean
>     Prompt: No build_forced no-CBs CPUs
>       Defined at: file:X
>       Depends on: <choice>
>       Location:
>         -> blabla -> Build-forced no-CBs CPUs (<choice> (=y>)

Thank you for the info, Yann!

							Thanx, Paul

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