Re: [PATCH tip/core/rcu 8/9] nohz_full: Add full-system-idle state machine

Geert Uytterhoeven
2013-09-06T18:50:43Z

On Fri, Sep 6, 2013 at 7:30 PM, Paul E. McKenney
<paulmck@linux.vnet.ibm.com> wrote:
>> Furthermore, it seems only hexagon, metag, mips, and x86 set NR_CPUS to 1
>> if !SMP. On other architectures, NR_CPUS is not defined and presumed to be 0.
>
> Would it make sense to require that NR_CPUS=1 for !SMP?

Yes, this looks reasonable to me.

> I tried creating a NR_CPUS_REALLY as follows:
>
> config NR_CPUS_REALLY
> int "Fixed version of NR_CPUS"
> default NR_CPUS if NR_CPUS
> default 1 if !NR_CPUS
>
> But this still gave a warning on the first "default" even though it
> was not in effect. I also tried using Kconfig "if":

IIRC, it tries to use the first default first, so the below may work
(the "if SMP" is probably not needed):

config NR_CPUS_REALLY
int "Fixed version of NR_CPUS"
default 1 if !SMP
default NR_CPUS if SMP

> Defining NR_CPUS=1 if !SMP is looking pretty good to me just now.
> This would probably have other benefits -- I cannot be the only
> person who ever wanted this. ;-)

Sure. I just didn't want to create patches for all architectures without
having a discussion first.

And it would be nice if it cuould be done in a central place, without
touching all architectures.

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds