linux-kernel - Re: [PATCH 206/208] x86/fpu: Add CONFIG_X86_DEBUG

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Date:	Wed, 6 May 2015 05:35:13 +0200
From:	Ingo Molnar <mingo2.kernel.org@...il.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	linux-kernel@...r.kernel.org,
	Andy Lutomirski <luto@...capital.net>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 206/208] x86/fpu: Add CONFIG_X86_DEBUG_FPU=y FPU
 debugging code


* Borislav Petkov <bp@...en8.de> wrote:

> On Tue, May 05, 2015 at 07:58:30PM +0200, Ingo Molnar wrote:
> > There are various internal FPU state debugging checks that never
> > trigger in practice, but which are useful for FPU code development.
> > 
> > Separate these out into CONFIG_X86_DEBUG_FPU=y, and also add a
> > couple of new ones.
> > 
> > The size difference is about 0.5K of code on defconfig:
> > 
> >    text        data     bss          filename
> >    15028906    2578816  1638400      vmlinux
> >    15029430    2578816  1638400      vmlinux
> > 
> > ( Keep this enabled by default until the new FPU code is debugged. )
> > 
> > Cc: Andy Lutomirski <luto@...capital.net>
> > Cc: Borislav Petkov <bp@...en8.de>
> > Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> > Cc: Fenghua Yu <fenghua.yu@...el.com>
> > Cc: H. Peter Anvin <hpa@...or.com>
> > Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> > Cc: Oleg Nesterov <oleg@...hat.com>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Signed-off-by: Ingo Molnar <mingo@...nel.org>
> 
> ...
> 
> > diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
> > index a4c1b7dbf70e..d2a281bd5f45 100644
> > --- a/arch/x86/include/asm/fpu/internal.h
> > +++ b/arch/x86/include/asm/fpu/internal.h
> > @@ -59,6 +59,15 @@ extern void fpu__clear(struct fpu *fpu);
> >  extern void fpu__init_check_bugs(void);
> >  extern void fpu__resume_cpu(void);
> >  
> > +/*
> > + * Debugging facility:
> > + */
> > +#ifdef CONFIG_X86_DEBUG_FPU
> > +# define WARN_ON_FPU(x) WARN_ON_ONCE(x)
> > +#else
> > +# define WARN_ON_FPU(x) ({ 0; })
> 
> Shouldn't this be called FPU_WARN_ON() ?

So I wanted this to match the 'usual' WARN*() APIs in appearance, with 
only at the end a small signal that this is conditional on FPU 
debugging enabled. In terms of code, we should think of them as 
WARN_ON()s. Slapping FPU_ in front of them distracts from that IMHO.

No strong feelings though.

Thanks,

	Ingo
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