linux-kernel - [PATCH 2/2] powerpc: Use CONFIG_ARCH_HAS_FAST

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Date:	Tue, 16 Sep 2014 10:49:14 +1000
From:	Anton Blanchard <anton@...ba.org>
To:	benh@...nel.crashing.org, paulus@...ba.org, michael@...erman.id.au,
	torvalds@...ux-foundation.org
Cc:	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] powerpc: Use CONFIG_ARCH_HAS_FAST_MULTIPLIER

I ran some tests to compare hash_64 using shifts and multiplies.
The results:

POWER6:	~2x slower
POWER7: ~2x faster
POWER8: ~2x faster

Now we have a proper config option, select
CONFIG_ARCH_HAS_FAST_MULTIPLIER on POWER7 and POWER8.

Signed-off-by: Anton Blanchard <anton@...ba.org>
---

Index: b/arch/powerpc/platforms/Kconfig.cputype
===================================================================
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -116,10 +116,12 @@ config POWER6_CPU
 config POWER7_CPU
 	bool "POWER7"
 	depends on PPC_BOOK3S_64
+	select ARCH_HAS_FAST_MULTIPLIER
 
 config POWER8_CPU
 	bool "POWER8"
 	depends on PPC_BOOK3S_64
+	select ARCH_HAS_FAST_MULTIPLIER
 
 config E5500_CPU
 	bool "Freescale e5500"
--
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