linux-kernel - Re: [PATCH] ia64: minor Makefile simplification through use of cc-ifversion

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Message-ID: <20090724231511.GA20607@linux-os.sc.intel.com>
Date:	Fri, 24 Jul 2009 16:15:11 -0700
From:	Fenghua Yu <fenghua.yu@...el.com>
To:	Frans Pop <elendil@...net.nl>
Cc:	Peter Chubb <peterc@...ato.unsw.edu.au>,
	Sam Ravnborg <sam@...nborg.org>,
	"linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
	"linux-kbuild@...r.kernel.org" <linux-kbuild@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ia64: minor Makefile simplification through use of cc-ifversion

On Fri, Jul 24, 2009 at 11:23:11AM -0700, Frans Pop wrote:
> On Friday 24 July 2009, Peter Chubb wrote:
> > >>>>> "Sam" == Sam Ravnborg <sam@...nborg.org> writes:
> > Sam> The above change is correct.  But I really wonder if the original
> > Sam> code was correct?  Do we really only want to use the -mtune
> > Sam> options for this specific gcc version?  If this is indeed the
> > Sam> case this deserves a comment explaning this.
> >
> > I suspect it should be all compilers after this one.  -mtune=mckinley
> > didn't work very well in the early gcc 3 compilers and didn't exist in
> > version 2.
> 
> How would you like to handle that? As it is essentially a separate issue,
> my suggestion would be: apply my patch as is and then (if needed) commit
> a separate patch to fix the incorrect comparisons on top.

Between GCC version 3.4.0 and 4.3.3 (including 3.4.0 and 4.3.3), -mtune=merced is
implemented in GCC. Starting from 4.4.0, -mtune=merced is deprecated.

Even implemented in versions between 3.4.0 and 4.3.3, the -mtune=merced
feature has been broken in some of the versions. For example, GCC 4.1.2 reports
interanl tuning function errors during kernel building with -mtune=merced. Or GCC
Bugzilla 16130 reports another -mtune=merced issue on GCC 3.4.1.

So I would remove the -mtune=merced from IA64 kernel build. Without this option,
kernel on Merced will remain the same except losing an unstable and out-of-date
performance tunning feature.

Since GCC version 3.4.0, -mtune=mckinley has been implemented. The
-mtune=mckinley option functions the same as mtune=itanium2. And mtune=itanium2
is the default option. So we don't need to add mtune=mckinley either since its
been the default option in any GCC version which implements this option.

Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>

---
 arch/ia64/Makefile |    5 -----
 1 files changed, 5 deletions(-)

diff --git a/arch/ia64/Makefile b/arch/ia64/Makefile
index 58a7e46..e7cbaa0 100644
--- a/arch/ia64/Makefile
+++ b/arch/ia64/Makefile
@@ -41,11 +41,6 @@ $(error Sorry, you need a newer version of the assember, one that is built from
 		ftp://ftp.hpl.hp.com/pub/linux-ia64/gas-030124.tar.gz)
 endif
 
-ifeq ($(call cc-version),0304)
-	cflags-$(CONFIG_ITANIUM)	+= -mtune=merced
-	cflags-$(CONFIG_MCKINLEY)	+= -mtune=mckinley
-endif
-
 KBUILD_CFLAGS += $(cflags-y)
 head-y := arch/ia64/kernel/head.o arch/ia64/kernel/init_task.o
 
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