linux-kernel - Re: [PATCH v3 -next 3/5] arm: Add support for LZ4-compressed kernel

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Date:	Tue, 30 Apr 2013 13:56:02 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Kyungsik Lee <kyungsik.lee@....com>
Cc:	Russell King <linux@....linux.org.uk>,
	"H. Peter Anvin" <hpa@...or.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-kbuild@...r.kernel.org, x86@...nel.org,
	celinux-dev@...ts.celinuxforum.org,
	Nicolas Pitre <nico@...xnic.net>,
	David Sterba <dsterba@...e.cz>,
	Nitin Gupta <nitingupta910@...il.com>,
	Joe Millenbach <jmillenbach@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Michal Marek <mmarek@...e.cz>, hyojun.im@....com,
	chan.jeong@....com, raphael.andy.lee@...il.com
Subject: Re: [PATCH v3 -next 3/5] arm: Add support for LZ4-compressed kernel

On Tue,  5 Mar 2013 20:47:34 +0900 Kyungsik Lee <kyungsik.lee@....com> wrote:

> This patch integrates the LZ4 decompression code to the arm pre-boot code.
> And it depends on two patchs below
> 
> lib: Add support for LZ4-compressed kernel
> decompressor: Add LZ4 decompressor module
> 
> ...
>
> - Apply CFLAGS, -Os to decompress.o to improve decompress
>   performance during boot-up process
>
> ...
>
> --- a/arch/arm/boot/compressed/Makefile
> +++ b/arch/arm/boot/compressed/Makefile
> @@ -24,6 +24,9 @@ endif
>  AFLAGS_head.o += -DTEXT_OFFSET=$(TEXT_OFFSET)
>  HEAD	= head.o
>  OBJS	+= misc.o decompress.o
> +ifeq ($(CONFIG_KERNEL_LZ4),y)
> +CFLAGS_decompress.o := -Os
> +endif

Surprised.  You found that -Os produces faster code than -O2?  Details,
please?

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