From 79ab11cdb90d8536817ab7357ecb6b1ff76be26c Mon Sep 17 00:00:00 2001 From: Christian Borntraeger Date: Tue, 25 Oct 2016 11:03:11 +0200 Subject: locking/core: Introduce cpu_relax_yield() For spinning loops people do often use barrier() or cpu_relax(). For most architectures cpu_relax and barrier are the same, but on some architectures cpu_relax can add some latency. For example on power,sparc64 and arc, cpu_relax can shift the CPU towards other hardware threads in an SMT environment. On s390 cpu_relax does even more, it uses an hypercall to the hypervisor to give up the timeslice. In contrast to the SMT yielding this can result in larger latencies. In some places this latency is unwanted, so another variant "cpu_relax_lowlatency" was introduced. Before this is used in more and more places, lets revert the logic and provide a cpu_relax_yield that can be called in places where yielding is more important than latency. By default this is the same as cpu_relax on all architectures. Signed-off-by: Christian Borntraeger Signed-off-by: Peter Zijlstra (Intel) Cc: Catalin Marinas Cc: Heiko Carstens Cc: Linus Torvalds Cc: Martin Schwidefsky Cc: Nicholas Piggin Cc: Noam Camus Cc: Peter Zijlstra Cc: Russell King Cc: Thomas Gleixner Cc: Will Deacon Cc: linuxppc-dev@lists.ozlabs.org Cc: virtualization@lists.linux-foundation.org Cc: xen-devel@lists.xenproject.org Link: http://lkml.kernel.org/r/1477386195-32736-2-git-send-email-borntraeger@de.ibm.com Signed-off-by: Ingo Molnar --- arch/sparc/include/asm/processor_32.h | 1 + arch/sparc/include/asm/processor_64.h | 1 + 2 files changed, 2 insertions(+) (limited to 'arch/sparc') diff --git a/arch/sparc/include/asm/processor_32.h b/arch/sparc/include/asm/processor_32.h index 812fd08f3e62..50e908a3c651 100644 --- a/arch/sparc/include/asm/processor_32.h +++ b/arch/sparc/include/asm/processor_32.h @@ -119,6 +119,7 @@ extern struct task_struct *last_task_used_math; int do_mathemu(struct pt_regs *regs, struct task_struct *fpt); #define cpu_relax() barrier() +#define cpu_relax_yield() cpu_relax() #define cpu_relax_lowlatency() cpu_relax() extern void (*sparc_idle)(void); diff --git a/arch/sparc/include/asm/processor_64.h b/arch/sparc/include/asm/processor_64.h index ce2595c89471..3e8fac724f18 100644 --- a/arch/sparc/include/asm/processor_64.h +++ b/arch/sparc/include/asm/processor_64.h @@ -216,6 +216,7 @@ unsigned long get_wchan(struct task_struct *task); "nop\n\t" \ ".previous" \ ::: "memory") +#define cpu_relax_yield() cpu_relax() #define cpu_relax_lowlatency() cpu_relax() /* Prefetch support. This is tuned for UltraSPARC-III and later. -- cgit v1.2.3