linux-kernel - Re: [PATCH] Use -mskip-rax-setup if supported

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Message-ID: <20150416212551.GY2366@two.firstfloor.org>
Date:	Thu, 16 Apr 2015 23:25:51 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	"H.J. Lu" <hjl.tools@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH] Use -mskip-rax-setup if supported

On Thu, Apr 16, 2015 at 02:23:44PM -0700, H.J. Lu wrote:
> GCC 5 added a compiler option, -mskip-rax-setup, for x86-64.  It skips
> setting up the RAX register when SSE is disabled and there are no
> variable arguments passed in vector registers.  Since kernel doesn't
> pass vector registers to functions with variable arguments, this option
> can be used to optimize the x86-64 kernel.  For kernel 3.17:
> 
>     text   data    bss    dec      hex   filename
> 11455921 2204048 5853184 19513153 129bf41 vmlinux #with -mskip-rax-setup
> 11480079 2204048 5853184 19537311 12a1d9f vmlinux

Patch looks good to me.

Reviewed-by: Andi Kleen <ak@...ux.intel.com>

-Andi
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