* [PATCH v2] cpumask: limit visibility of FORCE_NR_CPUS
@ 2022-10-19 22:59 Yury Norov
2022-11-04 17:43 ` Valentin Schneider
0 siblings, 1 reply; 6+ messages in thread
From: Yury Norov @ 2022-10-19 22:59 UTC (permalink / raw)
To: linux-kernel, Geert Uytterhoeven, Linus Torvalds,
Andy Shevchenko, Rasmus Villemoes, Andrew Morton,
Stephen Rothwell, Peter Zijlstra, Thomas Gleixner,
Paul E . McKenney, Vlastimil Babka, Dmitry Vyukov,
Valentin Schneider, Sander Vanheule, Alexey Klimov, Eric Biggers
Cc: 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.
The 'choice' and unused 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.
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>
---
v2: extend commit message with an explanation for what we need 'choice'.
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
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH v2] cpumask: limit visibility of FORCE_NR_CPUS
2022-10-19 22:59 [PATCH v2] cpumask: limit visibility of FORCE_NR_CPUS Yury Norov
@ 2022-11-04 17:43 ` Valentin Schneider
2022-11-04 22:36 ` Yury Norov
0 siblings, 1 reply; 6+ messages in thread
From: Valentin Schneider @ 2022-11-04 17:43 UTC (permalink / raw)
To: Yury Norov, linux-kernel, Geert Uytterhoeven, Linus Torvalds,
Andy Shevchenko, Rasmus Villemoes, Andrew Morton,
Stephen Rothwell, Peter Zijlstra, Thomas Gleixner,
Paul E . McKenney, Vlastimil Babka, Dmitry Vyukov,
Sander Vanheule, Alexey Klimov, Eric Biggers
Cc: Yury Norov
On 19/10/22 15:59, 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.
>
> The 'choice' and unused 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.
>
> 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>
> ---
> v2: extend commit message with an explanation for what we need 'choice'.
>
> 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
What about moving the 'depends on EXPERT' onto FORCE_NR_CPUS? I find it
makes it easier to figure out the requirements for that option, and is
similar to how e.g. CONFIG_PREEMPT_RT is handled.
> + 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
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] cpumask: limit visibility of FORCE_NR_CPUS
2022-11-04 17:43 ` Valentin Schneider
@ 2022-11-04 22:36 ` Yury Norov
2022-11-07 12:45 ` Valentin Schneider
0 siblings, 1 reply; 6+ messages in thread
From: Yury Norov @ 2022-11-04 22:36 UTC (permalink / raw)
To: Valentin Schneider
Cc: linux-kernel, Geert Uytterhoeven, Linus Torvalds,
Andy Shevchenko, Rasmus Villemoes, Andrew Morton,
Stephen Rothwell, Peter Zijlstra, Thomas Gleixner,
Paul E . McKenney, Vlastimil Babka, Dmitry Vyukov,
Sander Vanheule, Alexey Klimov, Eric Biggers
On Fri, Nov 04, 2022 at 05:43:53PM +0000, Valentin Schneider wrote:
> On 19/10/22 15:59, 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.
> >
> > The 'choice' and unused 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.
> >
> > 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>
> > ---
> > v2: extend commit message with an explanation for what we need 'choice'.
> >
> > 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
>
> What about moving the 'depends on EXPERT' onto FORCE_NR_CPUS? I find it
> makes it easier to figure out the requirements for that option, and is
> similar to how e.g. CONFIG_PREEMPT_RT is handled.
In case of PREEMPT_RT, there are some other options to choose. In case of
FORCE_NR_CPUS there will be a choice with a single option, and it would be
weird that the option is never used.
I'd prefer to hide this choice for non-experts entirely.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] cpumask: limit visibility of FORCE_NR_CPUS
2022-11-04 22:36 ` Yury Norov
@ 2022-11-07 12:45 ` Valentin Schneider
2022-11-07 17:55 ` Linus Torvalds
0 siblings, 1 reply; 6+ messages in thread
From: Valentin Schneider @ 2022-11-07 12:45 UTC (permalink / raw)
To: Yury Norov
Cc: linux-kernel, Geert Uytterhoeven, Linus Torvalds,
Andy Shevchenko, Rasmus Villemoes, Andrew Morton,
Stephen Rothwell, Peter Zijlstra, Thomas Gleixner,
Paul E . McKenney, Vlastimil Babka, Dmitry Vyukov,
Sander Vanheule, Alexey Klimov, Eric Biggers
On 04/11/22 15:36, Yury Norov wrote:
> On Fri, Nov 04, 2022 at 05:43:53PM +0000, Valentin Schneider wrote:
>> On 19/10/22 15:59, Yury Norov wrote:
>> > +choice
>> > + prompt "Number of CPUs detection method"
>> > + default UNFORCE_NR_CPUS
>> > + depends on SMP && EXPERT
>>
>> What about moving the 'depends on EXPERT' onto FORCE_NR_CPUS? I find it
>> makes it easier to figure out the requirements for that option, and is
>> similar to how e.g. CONFIG_PREEMPT_RT is handled.
>
> In case of PREEMPT_RT, there are some other options to choose. In case of
> FORCE_NR_CPUS there will be a choice with a single option, and it would be
> weird that the option is never used.
>
True, this would have been neater as a single config, but AIUI it's a
required "trick" for allyesconfig. I would have expected other configs to
have hit similar issues in the past, but didn't find any.
> I'd prefer to hide this choice for non-experts entirely.
Sure.
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] cpumask: limit visibility of FORCE_NR_CPUS
2022-11-07 12:45 ` Valentin Schneider
@ 2022-11-07 17:55 ` Linus Torvalds
2022-11-07 18:20 ` Yury Norov
0 siblings, 1 reply; 6+ messages in thread
From: Linus Torvalds @ 2022-11-07 17:55 UTC (permalink / raw)
To: Valentin Schneider
Cc: Yury Norov, linux-kernel, Geert Uytterhoeven, Andy Shevchenko,
Rasmus Villemoes, Andrew Morton, Stephen Rothwell,
Peter Zijlstra, Thomas Gleixner, Paul E . McKenney,
Vlastimil Babka, Dmitry Vyukov, Sander Vanheule, Alexey Klimov,
Eric Biggers
On Mon, Nov 7, 2022 at 4:45 AM Valentin Schneider <vschneid@redhat.com> wrote:
>
> True, this would have been neater as a single config, but AIUI it's a
> required "trick" for allyesconfig. I would have expected other configs to
> have hit similar issues in the past, but didn't find any.
Actually, the standard trick for allmodconfig and allyesconfig is to
use the "COMPILE_TEST" config variable.
It's basically a variable for "I'm not going to *run* the result, but
I want to make sure to get build coverage".
And both allmodconfig and allyesconfig set that config option.
In most cases, the "COMPILE_TEST" config variable is used to enable
things that wouldn't make sense on the chosen hardware platform, so
you have things like
depends on ARCH_DAVINCI || COMPILE_TEST
because some driver only makes sense on ARCH_DAVINCI, but people still
want the build coverage.
But sometimes it's used the other way around, so fro example on x86 we have
config X86_DECODER_SELFTEST
which explicitly depends on COMPILE_TEST *not* being set, because it's
a test that takes forever to run (particularly for huge kernels), and
so it's actually disabled for the common all{yes,mod}config cases.
Same goes for things like LTO_CLANG_FULL. It's just expensive for big
build tests, plus causes too many issues for now.
End result: if some option actually *reduces* test coverage, or has
some other reason why it makes no sense for build tests, use that
depends on !COMPILE_TEST
to not have allmodconfig and allyesconfig pick it.
Linus
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] cpumask: limit visibility of FORCE_NR_CPUS
2022-11-07 17:55 ` Linus Torvalds
@ 2022-11-07 18:20 ` Yury Norov
0 siblings, 0 replies; 6+ messages in thread
From: Yury Norov @ 2022-11-07 18:20 UTC (permalink / raw)
To: Linus Torvalds
Cc: Valentin Schneider, linux-kernel, Geert Uytterhoeven,
Andy Shevchenko, Rasmus Villemoes, Andrew Morton,
Stephen Rothwell, Peter Zijlstra, Thomas Gleixner,
Paul E . McKenney, Vlastimil Babka, Dmitry Vyukov,
Sander Vanheule, Alexey Klimov, Eric Biggers
On Mon, Nov 07, 2022 at 09:55:34AM -0800, Linus Torvalds wrote:
> On Mon, Nov 7, 2022 at 4:45 AM Valentin Schneider <vschneid@redhat.com> wrote:
> >
> > True, this would have been neater as a single config, but AIUI it's a
> > required "trick" for allyesconfig. I would have expected other configs to
> > have hit similar issues in the past, but didn't find any.
>
> Actually, the standard trick for allmodconfig and allyesconfig is to
> use the "COMPILE_TEST" config variable.
>
> It's basically a variable for "I'm not going to *run* the result, but
> I want to make sure to get build coverage".
>
> And both allmodconfig and allyesconfig set that config option.
>
> In most cases, the "COMPILE_TEST" config variable is used to enable
> things that wouldn't make sense on the chosen hardware platform, so
> you have things like
>
> depends on ARCH_DAVINCI || COMPILE_TEST
>
> because some driver only makes sense on ARCH_DAVINCI, but people still
> want the build coverage.
>
> But sometimes it's used the other way around, so fro example on x86 we have
>
> config X86_DECODER_SELFTEST
>
> which explicitly depends on COMPILE_TEST *not* being set, because it's
> a test that takes forever to run (particularly for huge kernels), and
> so it's actually disabled for the common all{yes,mod}config cases.
>
> Same goes for things like LTO_CLANG_FULL. It's just expensive for big
> build tests, plus causes too many issues for now.
>
> End result: if some option actually *reduces* test coverage, or has
> some other reason why it makes no sense for build tests, use that
>
> depends on !COMPILE_TEST
>
> to not have allmodconfig and allyesconfig pick it.
Thanks, I'll send v3 than.
Thanks,
Yury
^ permalink raw reply [flat|nested] 6+ messages in thread
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2022-10-19 22:59 [PATCH v2] cpumask: limit visibility of FORCE_NR_CPUS Yury Norov
2022-11-04 17:43 ` Valentin Schneider
2022-11-04 22:36 ` Yury Norov
2022-11-07 12:45 ` Valentin Schneider
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