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| author | Christian Borntraeger <borntraeger@de.ibm.com> | 2016-10-25 11:03:11 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2016-11-16 10:15:09 +0100 |
| commit | 79ab11cdb90d8536817ab7357ecb6b1ff76be26c (patch) | |
| tree | 98d7dde008cd59664f62105ad1a348ff7edfb6de /arch/xtensa/include/asm | |
| parent | 0f5225b024d4bffd682aab008c35862e8fdc1865 (diff) | |
| download | op-kernel-dev-79ab11cdb90d8536817ab7357ecb6b1ff76be26c.zip op-kernel-dev-79ab11cdb90d8536817ab7357ecb6b1ff76be26c.tar.gz | |
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 <borntraeger@de.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Noam Camus <noamc@ezchip.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
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 <mingo@kernel.org>
Diffstat (limited to 'arch/xtensa/include/asm')
| -rw-r--r-- | arch/xtensa/include/asm/processor.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/xtensa/include/asm/processor.h b/arch/xtensa/include/asm/processor.h index b42d68b..fe14dc2 100644 --- a/arch/xtensa/include/asm/processor.h +++ b/arch/xtensa/include/asm/processor.h @@ -206,6 +206,7 @@ extern unsigned long get_wchan(struct task_struct *p); #define KSTK_ESP(tsk) (task_pt_regs(tsk)->areg[1]) #define cpu_relax() barrier() +#define cpu_relax_yield() cpu_relax() #define cpu_relax_lowlatency() cpu_relax() /* Special register access. */ |
