[PATCH] Clarify CONFIG_DEBUG_INFO's bloaty nature

[PATCH] Clarify CONFIG_DEBUG_INFO's bloaty nature

[Borislav Petkov]

From: Borislav Petkov <bp@suse.de>

Hold down when it makes sense to enable CONFIG_DEBUG_INFO and when
CONFIG_KALLSYMS suffices.

Signed-off-by: Borislav Petkov <bp@suse.de>
Link: http://lkml.kernel.org/r/CA%2B55aFw_xs1tUteDrXz21QZB7BFk5p%2BF5NZ-SpV=CUVjeFwapA@mail.gmail.com
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
---
 lib/Kconfig.debug | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index dbf94a7d25a8..9095c2078095 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -126,7 +126,11 @@ config DEBUG_INFO
 	  This adds debug symbols to the kernel and modules (gcc -g), and
 	  is needed if you intend to use kernel crashdump or binary object
 	  tools like crash, kgdb, LKCD, gdb, etc on the kernel.
-	  Say Y here only if you plan to debug the kernel.
+
+	  If you only want to have resolved symbols in kernel traces and
+	  are not going to need support for those tools above, you don't need
+	  to enable this as it is a huge bloat and build slowdown;
+	  enable CONFIG_KALLSYMS instead.
 
 	  If unsure, say N.
 
-- 
1.8.5.2.192.g7794a68

Re: [PATCH] Clarify CONFIG_DEBUG_INFO's bloaty nature

[David Rientjes]

On Mon, 3 Feb 2014, Borislav Petkov wrote:

> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index dbf94a7d25a8..9095c2078095 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -126,7 +126,11 @@ config DEBUG_INFO
>  	  This adds debug symbols to the kernel and modules (gcc -g), and
>  	  is needed if you intend to use kernel crashdump or binary object
>  	  tools like crash, kgdb, LKCD, gdb, etc on the kernel.
> -	  Say Y here only if you plan to debug the kernel.
> +
> +	  If you only want to have resolved symbols in kernel traces and
> +	  are not going to need support for those tools above, you don't need
> +	  to enable this as it is a huge bloat and build slowdown;

How do you define "huge bloat" if the size of vmlinux doesn't increase?  
Would some people consider that to be acceptable but now mysteriously 
confused because we don't know what "huge bloat" you're referring to?

It also begs the question about the meaning of DEBUG_INFO_REDUCED and this 
comment doesn't even allow us to see that it's an option.

So this doesn't look good.

> +	  enable CONFIG_KALLSYMS instead.
>  
>  	  If unsure, say N.
>  

Re: [PATCH] Clarify CONFIG_DEBUG_INFO's bloaty nature

[Linus Torvalds]

On Mon, Feb 3, 2014 at 2:00 PM, David Rientjes <rientjes@google.com> wrote:
>
> How do you define "huge bloat" if the size of vmlinux doesn't increase?

Don't be silly. The size of all the object files increase *hugely*.

This is my fs/builtin.o in my normal config:

  -rw-rw-r--. 1 torvalds torvalds  2838613 Feb  3 14:32 fs/built-in.o

and with the *reduced* debug info, ie .config diff as follows:

  +CONFIG_DEBUG_INFO=y
  +CONFIG_DEBUG_INFO_REDUCED=y

I get this:

  -rw-rw-r--. 1 torvalds torvalds 11793317 Feb  3 14:33 fs/built-in.o

iow, that "reduced" debug info is still more than 4x bigger than a
non-debug-info kernel.

David, if you don't think that debug-info bloats the build, you're in
huge *huge* denial. CONFIG_DEBUG_INFO (even with the "reduced" thing)
is ABSOLUTELY HORRIBLE CRAP.

> Would some people consider that to be acceptable but now mysteriously
> confused because we don't know what "huge bloat" you're referring to?

That >4x size increase doesn't match your idea of "huge bloat"?

The object files being much bigger really does screw you especially on
laptops that often have less memory and less capable IO subsystems.
The final links in particular tend to be much bigger and use much more
memory.

I suspect a lot of people are in denial about just how *horrible* the
overhead of debug builds are. And yeah, if you have oodles of memory
to cache things, it's not too bad. But you really want to have *lots*
of memory, because otherwise you won't be caching all those object
files in RAM, and your build easily becomes IO bound at link time. A
factor of four size difference will not be helping your poor slow
laptop disk..

                      Linus

Re: [PATCH] Clarify CONFIG_DEBUG_INFO's bloaty nature

[Andrew Morton]

On Mon, 3 Feb 2014 14:47:15 -0800 Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Mon, Feb 3, 2014 at 2:00 PM, David Rientjes <rientjes@google.com> wrote:
> >
> > How do you define "huge bloat" if the size of vmlinux doesn't increase?
> 
> Don't be silly. The size of all the object files increase *hugely*.

yup, I disable this in my allmodconfig testing, to great effect.

That being said, I do think the text should make clear that the bloat
is a compile-time impact and not a runtime one.  Something like

--- a/lib/Kconfig.debug~lib-kconfigdebug-clarify-config_debug_infos-bloaty-nature-fix
+++ a/lib/Kconfig.debug
@@ -128,9 +128,9 @@ config DEBUG_INFO
 	  tools like crash, kgdb, LKCD, gdb, etc on the kernel.
 
 	  If you only want to have resolved symbols in kernel traces and
-	  are not going to need support for those tools above, you don't need
-	  to enable this as it is a huge bloat and build slowdown;
-	  enable CONFIG_KALLSYMS instead.
+	  are not going to need support for the above tools, you don't need
+	  to enable this.  It hugely bloat object files' on-disk sizes and slows
+	  the build.  Enable CONFIG_KALLSYMS instead.
 
 	  If unsure, say N.
 
_

Re: [PATCH] Clarify CONFIG_DEBUG_INFO's bloaty nature

[David Rientjes]

On Mon, 3 Feb 2014, Andrew Morton wrote:

> > > How do you define "huge bloat" if the size of vmlinux doesn't increase?
> > 
> > Don't be silly. The size of all the object files increase *hugely*.
> 
> yup, I disable this in my allmodconfig testing, to great effect.
> 
> That being said, I do think the text should make clear that the bloat
> is a compile-time impact and not a runtime one.  Something like
> 
> --- a/lib/Kconfig.debug~lib-kconfigdebug-clarify-config_debug_infos-bloaty-nature-fix
> +++ a/lib/Kconfig.debug
> @@ -128,9 +128,9 @@ config DEBUG_INFO
>  	  tools like crash, kgdb, LKCD, gdb, etc on the kernel.
>  
>  	  If you only want to have resolved symbols in kernel traces and
> -	  are not going to need support for those tools above, you don't need
> -	  to enable this as it is a huge bloat and build slowdown;
> -	  enable CONFIG_KALLSYMS instead.
> +	  are not going to need support for the above tools, you don't need
> +	  to enable this.  It hugely bloat object files' on-disk sizes and slows
> +	  the build.  Enable CONFIG_KALLSYMS instead.
>  
>  	  If unsure, say N.
>  

Um, I still don't think this is right since CONFIG_DEBUG_INFO_REDUCED 
requires you to say yes here and that config option actually specifies 
the tools for which it is effective.  Are you suggesting that we decouple 
CONFIG_DEBUG_INFO from CONFIG_DEBUG_INFO_REDUCED and make 
CONFIG_DEBUG_INFO select the reduced variant?  Or... what?

Re: [PATCH] Clarify CONFIG_DEBUG_INFO's bloaty nature

[Borislav Petkov]

On Mon, Feb 03, 2014 at 02:57:18PM -0800, Andrew Morton wrote:
> On Mon, 3 Feb 2014 14:47:15 -0800 Linus Torvalds <torvalds@linux-foundation.org> wrote:
> 
> > On Mon, Feb 3, 2014 at 2:00 PM, David Rientjes <rientjes@google.com> wrote:
> > >
> > > How do you define "huge bloat" if the size of vmlinux doesn't increase?
> > 
> > Don't be silly. The size of all the object files increase *hugely*.
> 
> yup, I disable this in my allmodconfig testing, to great effect.
> 
> That being said, I do think the text should make clear that the bloat
> is a compile-time impact and not a runtime one.  Something like
> 
> --- a/lib/Kconfig.debug~lib-kconfigdebug-clarify-config_debug_infos-bloaty-nature-fix
> +++ a/lib/Kconfig.debug
> @@ -128,9 +128,9 @@ config DEBUG_INFO
>  	  tools like crash, kgdb, LKCD, gdb, etc on the kernel.
>  
>  	  If you only want to have resolved symbols in kernel traces and
> -	  are not going to need support for those tools above, you don't need
> -	  to enable this as it is a huge bloat and build slowdown;
> -	  enable CONFIG_KALLSYMS instead.
> +	  are not going to need support for the above tools, you don't need
> +	  to enable this.  It hugely bloat object files' on-disk sizes and slows
> +	  the build.  Enable CONFIG_KALLSYMS instead.

Yes, this is better.

Andrew, can you add that or you want me to send a new version?

Thanks.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
--

Re: [PATCH] Clarify CONFIG_DEBUG_INFO's bloaty nature

[Ingo Molnar]

* David Rientjes <rientjes@google.com> wrote:

> On Mon, 3 Feb 2014, Andrew Morton wrote:
> 
> > > > How do you define "huge bloat" if the size of vmlinux doesn't increase?
> > > 
> > > Don't be silly. The size of all the object files increase *hugely*.
> > 
> > yup, I disable this in my allmodconfig testing, to great effect.
> > 
> > That being said, I do think the text should make clear that the bloat
> > is a compile-time impact and not a runtime one.  Something like
> > 
> > --- a/lib/Kconfig.debug~lib-kconfigdebug-clarify-config_debug_infos-bloaty-nature-fix
> > +++ a/lib/Kconfig.debug
> > @@ -128,9 +128,9 @@ config DEBUG_INFO
> >  	  tools like crash, kgdb, LKCD, gdb, etc on the kernel.
> >  
> >  	  If you only want to have resolved symbols in kernel traces and
> > -	  are not going to need support for those tools above, you don't need
> > -	  to enable this as it is a huge bloat and build slowdown;
> > -	  enable CONFIG_KALLSYMS instead.
> > +	  are not going to need support for the above tools, you don't need
> > +	  to enable this.  It hugely bloat object files' on-disk sizes and slows
> > +	  the build.  Enable CONFIG_KALLSYMS instead.
> >  
> >  	  If unsure, say N.
> >  
> 
> Um, I still don't think this is right since 
> CONFIG_DEBUG_INFO_REDUCED requires you to say yes here and that 
> config option actually specifies the tools for which it is 
> effective.  Are you suggesting that we decouple CONFIG_DEBUG_INFO 
> from CONFIG_DEBUG_INFO_REDUCED and make CONFIG_DEBUG_INFO select the 
> reduced variant?  Or... what?

I think the right solution is what I suggested in another recent 
discussion:

"So to reign in debuginfo in allyesconfig/allmodconfig builds we could 
 do something like:

 config SAVE_TIME_AND_DISK_SPACE
        bool "Faster and leaner build object files: compile without debug info"
        default y

 choice
        prompt "Choose DEBUGINFO bloat level"
        depends on !SAVE_TIME_AND_DISK_SPACE
        default DEBUG_INFO_REDUCED
        help
           This option allows to select the debuginfo model.

   config DEBUG_INFO_REDUCED
        bool "Reduced amount of debugging information, 4x regular .o size"

   config DEBUG_INFO
        bool "Full debuginfo, 10x regular .o size, 'planet killer' version"

 endchoice

 That would default to Y and would disable debuginfo by default."

Thanks,

	Ingo

Re: [PATCH] Clarify CONFIG_DEBUG_INFO's bloaty nature

[Linus Torvalds]

On Tue, Feb 4, 2014 at 1:08 AM, Ingo Molnar <mingo@kernel.org> wrote:
>
>  config SAVE_TIME_AND_DISK_SPACE
>         bool "Faster and leaner build object files: compile without debug info"
>         default y

Thinking about it, we already have this. It's called "CONFIG_COMPILE_TEST".

It very much gets set by all{yes,mod}config, and it also says "we're
interested in testing the compile, not so much running the result".

So let's just make the DEBUG_INFO depend on !COMPILE_TEST.

Trivial oneliner patch (independent of the discussion about improving
the documentation), so I'll just apply it.

I can't imagine that this would be controversial:

   config DEBUG_INFO
          bool "Compile the kernel with debug info"
  -       depends on DEBUG_KERNEL
  +       depends on DEBUG_KERNEL && !COMPILE_TEST
          help

Hm?

              Linus

Re: [PATCH] Clarify CONFIG_DEBUG_INFO's bloaty nature

[Andi Kleen]

Linus Torvalds <torvalds@linux-foundation.org> writes:
>
> Trivial oneliner patch (independent of the discussion about improving
> the documentation), so I'll just apply it.
>
> I can't imagine that this would be controversial:
>
>    config DEBUG_INFO
>           bool "Compile the kernel with debug info"
>   -       depends on DEBUG_KERNEL
>   +       depends on DEBUG_KERNEL && !COMPILE_TEST
>           help
>
> Hm?

I have used debug info on allyesconfig in the past to run statistics
on the resulting binary. It's still useful, even though quite slow.
Make it depend on !EXPERT or somesuch? I agree for normal usages it's fine.

BTW you probably also want to do the same for the x86 instruction
decoder test. It seems to be the biggest compile time waster in
allyesconfig and I usually disable it too.

-Andi
-- 
ak@linux.intel.com -- Speaking for myself only

Re: [PATCH] Clarify CONFIG_DEBUG_INFO's bloaty nature

[Linus Torvalds]

On Tue, Feb 4, 2014 at 9:32 AM, Andi Kleen <andi@firstfloor.org> wrote:
>
> I have used debug info on allyesconfig in the past to run statistics
> on the resulting binary. It's still useful, even though quite slow.
> Make it depend on !EXPERT or somesuch? I agree for normal usages it's fine.

EXPERT is useless, people set it randomly.

I'd suggest that for any statistics gathering, you just disable
COMPILE_TEST. You can do that by just editing the .config file after
doing the allyesconfig, or by pre-seeding the allyesconfig with
COMPILE_TEST disabled.

Your use-case is rather special, after all. I do *not* believe that we
should make one of the goals of "make all{yes,mod}config" be that kind
of odd specialized thing.

> BTW you probably also want to do the same for the x86 instruction
> decoder test. It seems to be the biggest compile time waster in
> allyesconfig and I usually disable it too.

Agreed, that should be disabled too by default. Although in that case
I think the COMPILE_TEST combination makes more sense, since it's a
coverage issue.

Suggestions for symbols?

                 Linus

Re: [PATCH] Clarify CONFIG_DEBUG_INFO's bloaty nature

[Ingo Molnar]

* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Tue, Feb 4, 2014 at 1:08 AM, Ingo Molnar <mingo@kernel.org> wrote:
> >
> >  config SAVE_TIME_AND_DISK_SPACE
> >         bool "Faster and leaner build object files: compile without debug info"
> >         default y
> 
> Thinking about it, we already have this. It's called "CONFIG_COMPILE_TEST".
> 
> It very much gets set by all{yes,mod}config, and it also says "we're
> interested in testing the compile, not so much running the result".
> 
> So let's just make the DEBUG_INFO depend on !COMPILE_TEST.
> 
> Trivial oneliner patch (independent of the discussion about improving
> the documentation), so I'll just apply it.
> 
> I can't imagine that this would be controversial:
> 
>    config DEBUG_INFO
>           bool "Compile the kernel with debug info"
>   -       depends on DEBUG_KERNEL
>   +       depends on DEBUG_KERNEL && !COMPILE_TEST
>           help
> 
> Hm?

Fully agreed.

Thanks,

	Ingo

[PATCH] x86: Disable CONFIG_X86_DECODER_SELFTEST in allmod/allyesconfigs

[Ingo Molnar]

* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> > BTW you probably also want to do the same for the x86 instruction 
> > decoder test. It seems to be the biggest compile time waster in 
> > allyesconfig and I usually disable it too.
> 
> Agreed, that should be disabled too by default. Although in that 
> case I think the COMPILE_TEST combination makes more sense, since 
> it's a coverage issue.

I'd say randconfig will cover it often enough, and the failure is also 
borderline build coverage related: you cannot really make the decoder 
test fail via source level changes, only with changes in the build 
environment, so I agree with Andi that we can disable this one too - 
via the patch below.

Thanks,

	Ingo

Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index 0f3621e..f0fca39 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -184,6 +184,11 @@ config HAVE_MMIOTRACE_SUPPORT
 config X86_DECODER_SELFTEST
 	bool "x86 instruction decoder selftest"
 	depends on DEBUG_KERNEL && KPROBES
+	#
+	# It can take some time to validate the image,
+	# make sure {allyes|allmod}config doesn't enable it:
+	#
+	depends on !COMPILE_TEST
 	---help---
 	 Perform x86 instruction decoder selftests at build time.
 	 This option is useful for checking the sanity of x86 instruction

Re: [PATCH] x86: Disable CONFIG_X86_DECODER_SELFTEST in allmod/allyesconfigs

[Paul Gortmaker]

On Wed, Feb 5, 2014 at 12:51 AM, Ingo Molnar <mingo@kernel.org> wrote:
>
> * Linus Torvalds <torvalds@linux-foundation.org> wrote:
>
>> > BTW you probably also want to do the same for the x86 instruction
>> > decoder test. It seems to be the biggest compile time waster in
>> > allyesconfig and I usually disable it too.
>>
>> Agreed, that should be disabled too by default. Although in that
>> case I think the COMPILE_TEST combination makes more sense, since
>> it's a coverage issue.
>
> I'd say randconfig will cover it often enough, and the failure is also
> borderline build coverage related: you cannot really make the decoder
> test fail via source level changes, only with changes in the build
> environment, so I agree with Andi that we can disable this one too -
> via the patch below.

For the record, even with a (currently) modern CPU such as a
Xeon E5-2630 @ 2.30GHz, the script takes 4m30s on 3.14-rc1
i386 allyesconfig.  And since it runs single threaded at the end
of the build, it really adds that amount to the wall time spent
on the build. So enthusiastically Acked, FWIW.

Paul.
--

>
> Thanks,
>
>         Ingo
>
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
>
> diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
> index 0f3621e..f0fca39 100644
> --- a/arch/x86/Kconfig.debug
> +++ b/arch/x86/Kconfig.debug
> @@ -184,6 +184,11 @@ config HAVE_MMIOTRACE_SUPPORT
>  config X86_DECODER_SELFTEST
>         bool "x86 instruction decoder selftest"
>         depends on DEBUG_KERNEL && KPROBES
> +       #
> +       # It can take some time to validate the image,
> +       # make sure {allyes|allmod}config doesn't enable it:
> +       #
> +       depends on !COMPILE_TEST
>         ---help---
>          Perform x86 instruction decoder selftests at build time.
>          This option is useful for checking the sanity of x86 instruction
> --
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Re: [PATCH] x86: Disable CONFIG_X86_DECODER_SELFTEST in allmod/allyesconfigs

[Andi Kleen]

> For the record, even with a (currently) modern CPU such as a
> Xeon E5-2630 @ 2.30GHz, the script takes 4m30s on 3.14-rc1
> i386 allyesconfig.  And since it runs single threaded at the end
> of the build, it really adds that amount to the wall time spent
> on the build. So enthusiastically Acked, FWIW.

I suppose we could just multi thread it. It should 
"embarassingly" scale without problems. But turning it off by default is a
first step.

-Andi

[tip:x86/urgent] x86/debug: Disable CONFIG_X86_DECODER_SELFTEST in allmod/allyesconfigs

[tip-bot for Ingo Molnar]

Commit-ID:  8c778d541bec8a41cbd8fa73b7cba90b2d6606c1
Gitweb:     http://git.kernel.org/tip/8c778d541bec8a41cbd8fa73b7cba90b2d6606c1
Author:     Ingo Molnar <mingo@kernel.org>
AuthorDate: Wed, 5 Feb 2014 06:51:37 +0100
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Sun, 9 Feb 2014 15:18:42 +0100

x86/debug: Disable CONFIG_X86_DECODER_SELFTEST in allmod/allyesconfigs

* Linus Torvalds <torvalds@linux-foundation.org> wrote:

Andi Kleen suggested to turn off CONFIG_X86_DECODER_SELFTEST=y
in allyesconfig, because it costs a lot of CPU time.

(In practice randconfig builds will cover this test frequently
 enough to provide build coverage.)

Suggested-by: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Richard Weinberger <richard@nod.at>
Cc: Borislav Petkov <bp@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140205055137.GB30094@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/Kconfig.debug | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index 321a52c..b542ec1 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -185,6 +185,11 @@ config X86_DECODER_SELFTEST
 	bool "x86 instruction decoder selftest"
 	depends on DEBUG_KERNEL && KPROBES
 	depends on !COMPILE_TEST
+	#
+	# It can take some time to validate the image,
+	# make sure {allyes|allmod}config doesn't enable it:
+	#
+	depends on !COMPILE_TEST
 	---help---
 	 Perform x86 instruction decoder selftests at build time.
 	 This option is useful for checking the sanity of x86 instruction

Re: [PATCH] x86: Disable CONFIG_X86_DECODER_SELFTEST in allmod/allyesconfigs

[Stephen Rothwell]

[-- Attachment #1: Type: text/plain, Size: 1866 bytes --]

Hi Ingo,

On Wed, 5 Feb 2014 06:51:37 +0100 Ingo Molnar <mingo@kernel.org> wrote:
>
> 
> * Linus Torvalds <torvalds@linux-foundation.org> wrote:
> 
> > > BTW you probably also want to do the same for the x86 instruction 
> > > decoder test. It seems to be the biggest compile time waster in 
> > > allyesconfig and I usually disable it too.
> > 
> > Agreed, that should be disabled too by default. Although in that 
> > case I think the COMPILE_TEST combination makes more sense, since 
> > it's a coverage issue.
> 
> I'd say randconfig will cover it often enough, and the failure is also 
> borderline build coverage related: you cannot really make the decoder 
> test fail via source level changes, only with changes in the build 
> environment, so I agree with Andi that we can disable this one too - 
> via the patch below.
> 
> Thanks,
> 
> 	Ingo
> 
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
> 
> diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
> index 0f3621e..f0fca39 100644
> --- a/arch/x86/Kconfig.debug
> +++ b/arch/x86/Kconfig.debug
> @@ -184,6 +184,11 @@ config HAVE_MMIOTRACE_SUPPORT
>  config X86_DECODER_SELFTEST
>  	bool "x86 instruction decoder selftest"
>  	depends on DEBUG_KERNEL && KPROBES
> +	#
> +	# It can take some time to validate the image,
> +	# make sure {allyes|allmod}config doesn't enable it:
> +	#
> +	depends on !COMPILE_TEST
>  	---help---
>  	 Perform x86 instruction decoder selftests at build time.
>  	 This option is useful for checking the sanity of x86 instruction

When this got applied to the tip tree, Linus had already applied an
earlier version as commit f8f202348208, and this one (commit
8c778d541bec) now duplicates the actual dependency in !COMPILE_TEST (but
does add a useful comment) ...

-- 
Cheers,
Stephen Rothwell <sfr@canb.auug.org.au>

[-- Attachment #2: Type: application/pgp-signature, Size: 836 bytes --]

Re: [PATCH] x86: Disable CONFIG_X86_DECODER_SELFTEST in allmod/allyesconfigs

[Ingo Molnar]

* Stephen Rothwell <sfr@canb.auug.org.au> wrote:

> Hi Ingo,
> 
> On Wed, 5 Feb 2014 06:51:37 +0100 Ingo Molnar <mingo@kernel.org> wrote:
> >
> > 
> > * Linus Torvalds <torvalds@linux-foundation.org> wrote:
> > 
> > > > BTW you probably also want to do the same for the x86 instruction 
> > > > decoder test. It seems to be the biggest compile time waster in 
> > > > allyesconfig and I usually disable it too.
> > > 
> > > Agreed, that should be disabled too by default. Although in that 
> > > case I think the COMPILE_TEST combination makes more sense, since 
> > > it's a coverage issue.
> > 
> > I'd say randconfig will cover it often enough, and the failure is also 
> > borderline build coverage related: you cannot really make the decoder 
> > test fail via source level changes, only with changes in the build 
> > environment, so I agree with Andi that we can disable this one too - 
> > via the patch below.
> > 
> > Thanks,
> > 
> > 	Ingo
> > 
> > Signed-off-by: Ingo Molnar <mingo@kernel.org>
> > 
> > diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
> > index 0f3621e..f0fca39 100644
> > --- a/arch/x86/Kconfig.debug
> > +++ b/arch/x86/Kconfig.debug
> > @@ -184,6 +184,11 @@ config HAVE_MMIOTRACE_SUPPORT
> >  config X86_DECODER_SELFTEST
> >  	bool "x86 instruction decoder selftest"
> >  	depends on DEBUG_KERNEL && KPROBES
> > +	#
> > +	# It can take some time to validate the image,
> > +	# make sure {allyes|allmod}config doesn't enable it:
> > +	#
> > +	depends on !COMPILE_TEST
> >  	---help---
> >  	 Perform x86 instruction decoder selftests at build time.
> >  	 This option is useful for checking the sanity of x86 instruction
> 
> When this got applied to the tip tree, Linus had already applied an 
> earlier version as commit f8f202348208, and this one (commit 
> 8c778d541bec) now duplicates the actual dependency in !COMPILE_TEST 
> (but does add a useful comment) ...

Ok, I've zapped it from x86/urgent, thanks for letting me know!

	Ingo