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arm64: atomics: avoid out-of-line ll/sc atomics

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When building for LSE atomics (CONFIG_ARM64_LSE_ATOMICS), if the hardware
or toolchain doesn't support it the existing code will fallback to ll/sc
atomics. It achieves this by branching from inline assembly to a function
that is built with special compile flags. Further this results in the
clobbering of registers even when the fallback isn't used increasing
register pressure.

Improve this by providing inline implementations of both LSE and
ll/sc and use a static key to select between them, which allows for the
compiler to generate better atomics code. Put the LL/SC fallback atomics
in their own subsection to improve icache performance.

Signed-off-by: Andrew Murray <andrew.murray@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Andrew Murray
2019-08-28 18:50:07 +01:00
committed by Will Deacon
parent 580fa1b874
commit addfc38672
6 changed files with 329 additions and 328 deletions
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arch/arm64/include/asm/cmpxchg.h
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@@ -10,7 +10,7 @@
#include <linux/build_bug.h>
#include <linux/compiler.h>
#include <asm/atomic.h>
#include <asm/atomic_arch.h>
#include <asm/barrier.h>
#include <asm/lse.h>