Dne 18.6.2015 v 10:45 Vineet Gupta napsal(a):
> On Thursday 18 June 2015 01:43 PM, Michal Marek wrote:
>>>> Alternatively, as we already have CONFIG_CC_OPTIMIZE_FOR_SIZE,
>>>> a(nother) Kconfig option may make sense.
>> We can also introduce some ARCH_CFLAGS that is appended near the end of
>> the list, and have arc/Makefile add its -O3 there. But I'd like to why
>> the -O3 needs to be there in first place.
>
> This is how historically ARC kernels have been built. We do track performance
> results LMBench/hackbench... and going from -O3 to -O2 caused a sudden dip in some
> of the numbers when we measured 3.18 (vs. 3.13)
>
>> Obviously, the kernel works
>> with -O2, otherwise the regression would have been identified earlier.
>
> Its a performance thing - so yeah -O2 works, but -O3 works even better :-)
>
>> So why can't users specify -O3 in KCFLAGS like on any other
>> architecture.
>
> Sweet, I didn't know about this. But I don't see any arch setting this - only tile
> using it. So yeah - below does the trick !
>
> --------->
> From 5e44cd2ed69b1d030b4cb87600d2767b69c35537 Mon Sep 17 00:00:00 2001
> From: Vineet Gupta <vgupta@xxxxxxxxxxxx>
> Date: Thu, 18 Jun 2015 13:54:01 +0530
> Subject: [PATCH] ARC: Override toplevel default -O2 with -O3
>
> ARC kernels have historically been built with -O3, despite top level
> Makefile defaulting to -O2. This was facilitated by implicitly ordering
> of arch makefile include AFTER top level assigned -O2.
>
> An upstream fix to top level a1c48bb160f ("Makefile: Fix unrecognized
> cross-compiler command line options") changed the ordering, making ARC
> -O3 defunt.
>
> Fix that by NOT relying on any ordering whatsoever and use the right
> mechanism to do the over-rides.
>
> Suggested-by: Michal Marek <mmarek@xxxxxxx>
> Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Vineet Gupta <vgupta@xxxxxxxxxxxx>
> ---
> arch/arc/Makefile | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/arc/Makefile b/arch/arc/Makefile
> index 86c71b2089d2..c23f3f2b0ff8 100644
> --- a/arch/arc/Makefile
> +++ b/arch/arc/Makefile
> @@ -44,6 +44,7 @@ endif
> ifndef CONFIG_CC_OPTIMIZE_FOR_SIZE
> # Generic build system uses -O2, we want -O3
> cflags-y += -O3
> +KCFLAGS += -O3
> endif
Uh, this is not what I meant. KCFLAGS is a *user* setting. It's meant to
be set in the environment or command line.
Michal
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