On Tue, Apr 30, 2013 at 01:56:02PM -0700, Andrew Morton wrote:
> On Tue, 5 Mar 2013 20:47:34 +0900 Kyungsik Lee <kyungsik.lee@xxxxxxx> 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?
-Os is enforced here, based on the test result of decompression time
below, slightly faster than -O2.
But further tests with UA show that using -O2 will be the right choice
especially in the case of the unaligned access enabled.
Decompression Time(counts)
UA
-Os 6717 3447
-O2 6720 2728
Note: ARM v7, Kernel 3.4
counter freq. = 32768 HZ
UA(Unaligned Access)
gcc version 4.6.2 (Ubuntu/Linaro 4.6.2-14ubuntu2~ppa1)
Thanks,
Kyungsik
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