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arm64: Implement cpu_relax as yield

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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>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Peter Crosthwaite 2015-03-02 19:19:14 +00:00 • committed by Will Deacon
parent 06e5801b8c
commit 1baa82f480
1 changed files with 5 additions and 1 deletions
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6
arch/arm64/include/asm/processor.h
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@ -127,7 +127,11 @@ extern void release_thread(struct task_struct *);
unsigned long get_wchan(struct task_struct *p); 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() #define cpu_relax_lowlatency() cpu_relax()
/* Thread switching */ /* Thread switching */