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
# small data is default for elf32 tool-chain. If not usable, disable it
--
1.9.1
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