From mboxrd@z Thu Jan 1 00:00:00 1970 From: will.deacon@arm.com (Will Deacon) Date: Wed, 25 Apr 2018 14:41:20 +0100 Subject: [PATCH] arm64: Select ARCH_HAS_FAST_MULTIPLIER In-Reply-To: <877b532d8d240c1d9e9db923c84b924443a218ed.1524583390.git.robin.murphy@arm.com> References: <877b532d8d240c1d9e9db923c84b924443a218ed.1524583390.git.robin.murphy@arm.com> Message-ID: <20180425134119.GE8383@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tue, Apr 24, 2018 at 04:25:47PM +0100, Robin Murphy wrote: > 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 > --- Acked-by: Will Deacon Will