Messages in this thread Patch in this message |  | | | From | Peter Crosthwaite <> | | Subject | [PATCH] arm64: Implement cpu_relax as yield | | Date | Mon, 2 Mar 2015 11:19:14 -0800 |
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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> --- arch/arm64/include/asm/processor.h | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h index f9be30e..ac2381d 100644 --- a/arch/arm64/include/asm/processor.h +++ b/arch/arm64/include/asm/processor.h @@ -126,7 +126,11 @@ 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 */ -- 2.3.0.1.g27a12f1
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