[PATCH] cpumask: limit visibility of FORCE_NR_CPUS

[PATCH] cpumask: limit visibility of FORCE_NR_CPUS

[Yury Norov]

In current form, FORCE_NR_CPUS is visible to all users building their
kernels, even not experts. It is also set in allmodconfig or allyesconfig,
which is not a correct behavior.

Suggested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Yury Norov <yury.norov@gmail.com>
---
 lib/Kconfig | 31 ++++++++++++++++++++++++-------
 1 file changed, 24 insertions(+), 7 deletions(-)

diff --git a/lib/Kconfig b/lib/Kconfig
index 9bbf8a4b2108..1ada12f5dda6 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -528,14 +528,31 @@ config CPUMASK_OFFSTACK
 	  them on the stack.  This is a bit more expensive, but avoids
 	  stack overflow.
 
+choice
+	prompt "Number of CPUs detection method"
+	default UNFORCE_NR_CPUS
+	depends on SMP && EXPERT
+	help
+	  Select between boot-time and compile-time detection of number
+	  of CPUs. If it's possible to provide exact number of CPUs at
+	  compile-time, kernel code may be optimized better.
+	  For general-purpose kernel, choose "boot time" option.
+
+config UNFORCE_NR_CPUS
+	bool "Set number of CPUs at boot time"
+	help
+	  Choose it if you build general-purpose kernel and want to rely
+	  on kernel to detect actual number of CPUs.
+
 config FORCE_NR_CPUS
-       bool "NR_CPUS is set to an actual number of CPUs"
-       depends on SMP
-       help
-         Say Yes if you have NR_CPUS set to an actual number of possible
-         CPUs in your system, not to a default value. This forces the core
-         code to rely on compile-time value and optimize kernel routines
-         better.
+	bool "Set number of CPUs at compile time"
+	help
+	  Choose it if NR_CPUS corresponds to an actual number of
+	  possible CPUs in your system. This forces the core code
+	  to rely on compile-time value and optimize kernel routines
+	  better.
+
+endchoice
 
 config CPU_RMAP
 	bool
-- 
2.34.1

Re: [PATCH] cpumask: limit visibility of FORCE_NR_CPUS

[Andy Shevchenko]

On Tue, Oct 18, 2022 at 10:22:00PM -0700, Yury Norov wrote:
> In current form, FORCE_NR_CPUS is visible to all users building their
> kernels, even not experts. It is also set in allmodconfig or allyesconfig,
> which is not a correct behavior.

Seems you forgot to update the commit message to explain the choise usage.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH] cpumask: limit visibility of FORCE_NR_CPUS

[Yury Norov]

On Wed, Oct 19, 2022 at 02:22:40PM +0300, Andy Shevchenko wrote:
> On Tue, Oct 18, 2022 at 10:22:00PM -0700, Yury Norov wrote:
> > In current form, FORCE_NR_CPUS is visible to all users building their
> > kernels, even not experts. It is also set in allmodconfig or allyesconfig,
> > which is not a correct behavior.
> 
> Seems you forgot to update the commit message to explain the choise usage.

OK, I'll fold-in something like this:

The 'choice' and sudo config UNFORCE_NR_CPUS are used to ensure that 
auto-generated configs that try to enable as much options as possible,
like allmodconfig, don't enable FORCE_NR_CPUS.

Is that what you mean?

Re: [PATCH] cpumask: limit visibility of FORCE_NR_CPUS

[Geert Uytterhoeven]

Hi Yuri,

On Wed, Oct 19, 2022 at 8:25 PM Yury Norov <yury.norov@gmail.com> wrote:
> On Wed, Oct 19, 2022 at 02:22:40PM +0300, Andy Shevchenko wrote:
> > On Tue, Oct 18, 2022 at 10:22:00PM -0700, Yury Norov wrote:
> > > In current form, FORCE_NR_CPUS is visible to all users building their
> > > kernels, even not experts. It is also set in allmodconfig or allyesconfig,
> > > which is not a correct behavior.
> >
> > Seems you forgot to update the commit message to explain the choise usage.
>
> OK, I'll fold-in something like this:
>
> The 'choice' and sudo config UNFORCE_NR_CPUS are used to ensure that

sudo?

> auto-generated configs that try to enable as much options as possible,
> like allmodconfig, don't enable FORCE_NR_CPUS.
>
> Is that what you mean?

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