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

From: Paul E. McKenney
Date: Tue Apr 30 2013 - 17:49:34 EST


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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