From: robin.murphy@arm.com (Robin Murphy)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] arm64: Select ARCH_HAS_FAST_MULTIPLIER
Date: Tue, 24 Apr 2018 16:25:47 +0100 [thread overview]
Message-ID: <877b532d8d240c1d9e9db923c84b924443a218ed.1524583390.git.robin.murphy@arm.com> (raw)
It is probably safe to assume that all Armv8-A implementations have a
multiplier whose efficiency is comparable or better than a sequence of
three or so register-dependent arithmetic instructions. Select
ARCH_HAS_FAST_MULTIPLIER to get ever-so-slightly nicer codegen in the
few dusty old corners which care.
In a contrived benchmark calling hweight64() in a loop, this does indeed
turn out to be a small win overall, with no measurable impact on
Cortex-A57 but about 5% performance improvement on Cortex-A53.
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
Apropos of stumbling across this option whilst digging down into some
bitmap-juggling code...
arch/arm64/Kconfig | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index eb2cf4938f6d..9c850f3b398f 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -12,6 +12,7 @@ config ARM64
select ARCH_HAS_DEVMEM_IS_ALLOWED
select ARCH_HAS_ACPI_TABLE_UPGRADE if ACPI
select ARCH_HAS_ELF_RANDOMIZE
+ select ARCH_HAS_FAST_MULTIPLIER
select ARCH_HAS_FORTIFY_SOURCE
select ARCH_HAS_GCOV_PROFILE_ALL
select ARCH_HAS_GIGANTIC_PAGE if (MEMORY_ISOLATION && COMPACTION) || CMA
--
2.17.0.dirty
next reply other threads:[~2018-04-24 15:25 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-24 15:25 Robin Murphy [this message]
2018-04-25 13:41 ` [PATCH] arm64: Select ARCH_HAS_FAST_MULTIPLIER Will Deacon
2018-05-16 10:51 ` Catalin Marinas
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