linux-kernel - Re: ACPI build problem (2.6.21 CONFIG_X86_64_ACPI

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Date:	Thu, 10 May 2007 04:04:17 -0400
From:	Len Brown <lenb@...nel.org>
To:	Ravikiran G Thirumalai <kiran@...lex86.org>
Cc:	Steven Whitehouse <swhiteho@...hat.com>, Andi Kleen <ak@...e.de>,
	Shai Fultheim <shai@...lex86.org>, linux-kernel@...r.kernel.org
Subject: Re: ACPI build problem (2.6.21 CONFIG_X86_64_ACPI_NUMA)

On Monday 30 April 2007 14:28, Ravikiran G Thirumalai wrote:
> On Sat, Apr 28, 2007 at 01:59:46AM -0400, Len Brown wrote:
> > On Thursday 26 April 2007 09:26, you wrote:
> > ... 
> > CONFIG_ACPI depends on CONFIG_PM, yet this build fails because you have
> > CONFIG_ACPI=y and CONFIG_PM=n
> > 
> > Unfortunately kconfig doesn't trace dependencies when "select" is used,
> > making select sort of evil.  Ie. select can't target anything which
> > itself has dependencies.
> > 
> > In 2.6.15, b0bd35e622ffbda2c01dc67a0381c6a18817a29a added the select below,
> > and subsequently ACPI became dependent on PM, which broke your build.
> > Technically, this could have broken your build in other ways too
> > since ACPI already had other dependencies.
> > 
> > +# Dummy CONFIG option to select ACPI_NUMA from drivers/acpi/Kconfig.
> > +
> > +config X86_64_ACPI_NUMA
> > +       bool "ACPI NUMA detection"
> > +       depends on NUMA
> > +       select ACPI 
> > +       select ACPI_NUMA
> > +       default y
> > +       help
> > +	 Enable ACPI SRAT based node topology detection.
> > 
> > If you de-select CONFIG_X86_64_ACPI_NUMA then the select goes away
> > and kconfig should work properly.
> > 
> > It isn't immediately clear to me how the NUMA Kconfig patch is a step
> > forward, but perhaps the authors can comment.
> >
> 
> Before the above change, to select NUMA for em64T systems, you *had* to
> select K8_NUMA in the 'Processor type and features'  sub menu to select
> CONFIG_NUMA, and then select ACPI NUMA from the generic PM menu, which is
> not very intuitive when you have a EM64T NUMA system.
> 
> On x86_64 platforms, NUMA topology detection could be K8 style detection,
> ACPI based topology  or NUMA emulation.  Most of the real NUMA systems
> would need ACPI detection, older AMD platforms would need K8_NUMA, and 
> NUMA emulation is a debugging/emulation option to emulate NUMA topology on
> a regular SMP box.  Since CONFIG_NUMA + CONFIG_NUMA_EMU is a valid
> combination, and since CONFIG_NUMA + CONFIG_K8_NUMA is a valid combination,
> it makes sense to have X86_64_ACPI_NUMA on its own, and grouped along with
> other NUMA topology styles in the Processor menu.  Hope this is good enough
> reason :)

well, you totally lost me on that, but maybe that was the point...
If the distros always get this right by selecting everything under the sun,
then it probably isn't worth the complexity of an additional option.
The number of people who build a numa-capable kernel and try to save
some text space by leaving out some options is likely a pretty small group.

> Regarding the subject build breakage, CONFIG_ACPI depends on CONFIG_PM with
> an explicit 'depends' keyword. If PM does not get selected and CONFIG_ACPI
> gets selected, I would think it is a Kconfig bug which needs fixing no?
> Else, we can add a workaround by selecting CONFIG_PM if X86_64_ACPI_NUMA is
> chosen.  But AFAICT the right thing is to fix the Kconfig bug.

Of course the "right thing to do" is to fix the kernel build sub-system.
But this issue has come up many times before and the fix has always
been to not use the existing build systems in ways that it breaks.

> > +# Dummy CONFIG option to select ACPI_NUMA from drivers/acpi/Kconfig.
> > +
> > +config X86_64_ACPI_NUMA
> > +       bool "ACPI NUMA detection"
> > +       depends on NUMA
> > +       select ACPI 

any chance you can depend on ACPI instead of selecting it?

> > +       select ACPI_NUMA
> > +       default y
> > +       help
> > +	 Enable ACPI SRAT based node topology detection.

-Len

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