Commit 1baa82f4 authored Mar 02, 2015 by Peter Crosthwaite Committed by Will Deacon Mar 17, 2015

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>

parent 06e5801b

arch/arm64/include/asm/processor.h

+5 −1

Original line number	Diff line number	Diff line
		@@ -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 */