linux-kernel - Re: [GIT PULL] scheduler fixes

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Date:	Thu, 1 Oct 2009 09:28:57 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <johnstul@...ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [GIT PULL] scheduler fixes

On Thu, Oct 01, 2009 at 08:42:09AM +0200, Ingo Molnar wrote:
> 
> * Eric Dumazet <eric.dumazet@...il.com> wrote:
> 
> > Ingo Molnar a écrit :
> > > 
> > > That's not enough - the inline assembly code in 
> > > arch/x86/include/asm/cmpxchg_32.h should also not reference 
> > > cmpxchg8b_emu in that case.
> > > 
> > 
> > I believe it is OK as is, since cmpxchg8b_emu is referenced only
> > once, in a section guarded by :
> > #ifndef CONFIG_X86_CMPXCHG64
> 
> yeah. But this bit is wrong:
> 
> > +++ b/arch/x86/lib/Makefile
> > @@ -15,8 +15,10 @@ ifeq ($(CONFIG_X86_32),y)
> >          obj-y += atomic64_32.o
> >          lib-y += checksum_32.o
> >          lib-y += strstr_32.o
> > -        lib-y += semaphore_32.o string_32.o cmpxchg8b_emu.o
> > -
> > +        lib-y += semaphore_32.o string_32.o
> > +ifeq ($(CONFIG_X86_CMPXCHG64),n)
> > +        lib-y += cmpxchg8b_emu.o
> > +endif
> >          lib-$(CONFIG_X86_USE_3DNOW) += mmx_32.o
> >  else
> >          obj-y += io_64.o iomap_copy_64.o
> 
> The way to check for a disabled option in a Make rule is:
> 
> 	ifneq ($(CONFIG_X86_CMPXCHG64),y)
or
 	ifeq ($(CONFIG_X86_CMPXCHG64),)

Both variants are suboptimal - but I have not been
able to come up with something readable in this situation.

Looking at the above the first is the better version as
it is a bit more obvious what we test for (assuming reader
knows this is a boolean value and not tristate).

	Sam
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