diff options
| author | Peter Crosthwaite <[email protected]> | 2015-03-02 19:19:14 +0000 |
|---|---|---|
| committer | Will Deacon <[email protected]> | 2015-03-17 10:17:29 +0000 |
| commit | 1baa82f48030f38d1895301f1ec93acbcb3d15db (patch) | |
| tree | 7d9e69cd915039f5fd62036351a4d78ad955b89c | |
| parent | 06e5801b8cb3fc057d88cb4dc03c0b64b2744cda (diff) | |
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 <[email protected]>
Acked-by: Will Deacon <[email protected]>
Signed-off-by: Will Deacon <[email protected]>
| -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 */ |