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| author | Peter Crosthwaite <peter.crosthwaite@xilinx.com> | 2015-03-02 20:19:14 +0100 |
|---|---|---|
| committer | Will Deacon <will.deacon@arm.com> | 2015-03-17 11:17:29 +0100 |
| commit | 1baa82f48030f38d1895301f1ec93acbcb3d15db (patch) | |
| tree | 7d9e69cd915039f5fd62036351a4d78ad955b89c /arch/arm64/include | |
| parent | Linux 4.0-rc4 (diff) | |
| download | linux-1baa82f48030f38d1895301f1ec93acbcb3d15db.tar.xz linux-1baa82f48030f38d1895301f1ec93acbcb3d15db.zip | |
arm64: Implement cpu_relax as yield
ARM64 has the yield nop hint which has the intended semantics of
cpu_relax. Implement.
The immediate application is ARM CPU emulators. An emulator can take
advantage of the yield hint to de-prioritise an emulated CPU in favor
of other emulation tasks. QEMU A64 SMP emulation has yield awareness,
and sees a significant boot time performance increase with this change.
Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Diffstat (limited to 'arch/arm64/include')
| -rw-r--r-- | arch/arm64/include/asm/processor.h | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h index 20e9591a60cf..d2c37a1df0eb 100644 --- a/arch/arm64/include/asm/processor.h +++ b/arch/arm64/include/asm/processor.h @@ -127,7 +127,11 @@ extern void release_thread(struct task_struct *); unsigned long get_wchan(struct task_struct *p); -#define cpu_relax() barrier() +static inline void cpu_relax(void) +{ + asm volatile("yield" ::: "memory"); +} + #define cpu_relax_lowlatency() cpu_relax() /* Thread switching */ |