linux-kernel - Re: [PATCH] x86: don't compile vsmp

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Message-ID: <20090228094430.GH12095@elte.hu>
Date:	Sat, 28 Feb 2009 10:44:30 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Ravikiran G Thirumalai <kiran@...lex86.org>
Cc:	Yinghai Lu <yinghai@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	shai@...lex86.org
Subject: Re: [PATCH] x86: don't compile vsmp_64 for 32bit


* Ravikiran G Thirumalai <kiran@...lex86.org> wrote:

> On Thu, Feb 26, 2009 at 12:44:57PM +0100, Ingo Molnar wrote:
> >
> >* Ravikiran G Thirumalai <kiran@...lex86.org> wrote:
> >
> >> On Wed, Feb 25, 2009 at 09:20:50PM -0800, Yinghai Lu wrote:
> >> >
> >> >Impact: cleanup
> >> >
> >> >that is only needed when CONFIG_X86_VSMP is defined with 64bit
> >> >also remove dead code about PCI, because CONFIG_X86_VSMP depends on PCI
> >> >
> >> >Signed-off-by: Yinghai Lu <yinghai@...nel.org>
> >> >
> >> 
> >> NAK!
> >> vsmp64.c is compiled unconditionally for a reason.  There are ifdefs in the
> >> file to avoid code compilation based on config options. is_vsmp_box() is
> >> needed even when CONFIG_X86_VSMP is not enabled, since distro kernels don't ship
> >> with CONFIG_X86_VSMP, and since is_vsmp_box() is used to determine  whether
> >> tsc's can be considered synced or not, this is needed.
> >
> >is_vsmp_box() is always available:
> 
> Yes.  But it does not really detect if the machine is vsmp.  
> It is just a 'return 0'.
> 
> >
> >> >+#ifdef CONFIG_X86_VSMP
> >> > extern int is_vsmp_box(void);
> >> >+#else
> >> >+static inline int is_vsmp_box(void)
> >> >+{
> >> >+	return 0;
> >> >+}
> >> >+#endif
> >
> >What this patch does is it reduces the kernel's size when 
> >CONFIG_X86_VSMP is turned off and also makes the code arguably 
> >cleaner.
> 
> True, but by how much? 212 bytes, out of 7285943 bytes which 
> is very very small percentage wise.

How does this eliminate the validity of the patch?

	Ingo
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