From: Martin Schwidefsky Date: Sun, 1 Oct 2006 06:27:43 +0000 (-0700) Subject: [PATCH] Directed yield: cpu_relax variants for spinlocks and rw-locks X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=ef6edc9746dc2bfdacf44eefd5f881179971c478;p=linux.git [PATCH] Directed yield: cpu_relax variants for spinlocks and rw-locks On systems running with virtual cpus there is optimization potential in regard to spinlocks and rw-locks. If the virtual cpu that has taken a lock is known to a cpu that wants to acquire the same lock it is beneficial to yield the timeslice of the virtual cpu in favour of the cpu that has the lock (directed yield). With CONFIG_PREEMPT="n" this can be implemented by the architecture without common code changes. Powerpc already does this. With CONFIG_PREEMPT="y" the lock loops are coded with _raw_spin_trylock, _raw_read_trylock and _raw_write_trylock in kernel/spinlock.c. If the lock could not be taken cpu_relax is called. A directed yield is not possible because cpu_relax doesn't know anything about the lock. To be able to yield the lock in favour of the current lock holder variants of cpu_relax for spinlocks and rw-locks are needed. The new _raw_spin_relax, _raw_read_relax and _raw_write_relax primitives differ from cpu_relax insofar that they have an argument: a pointer to the lock structure. Signed-off-by: Martin Schwidefsky Cc: Ingo Molnar Cc: Paul Mackerras Cc: Haavard Skinnemoen Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/include/asm-alpha/spinlock.h b/include/asm-alpha/spinlock.h index 0c294c9b0c558..aeeb125f68513 100644 --- a/include/asm-alpha/spinlock.h +++ b/include/asm-alpha/spinlock.h @@ -166,4 +166,8 @@ static inline void __raw_write_unlock(raw_rwlock_t * lock) lock->lock = 0; } +#define _raw_spin_relax(lock) cpu_relax() +#define _raw_read_relax(lock) cpu_relax() +#define _raw_write_relax(lock) cpu_relax() + #endif /* _ALPHA_SPINLOCK_H */ diff --git a/include/asm-arm/spinlock.h b/include/asm-arm/spinlock.h index 01b7c26a30386..861092fbaa532 100644 --- a/include/asm-arm/spinlock.h +++ b/include/asm-arm/spinlock.h @@ -218,4 +218,8 @@ static inline int __raw_read_trylock(raw_rwlock_t *rw) /* read_can_lock - would read_trylock() succeed? */ #define __raw_read_can_lock(x) ((x)->lock < 0x80000000) +#define _raw_spin_relax(lock) cpu_relax() +#define _raw_read_relax(lock) cpu_relax() +#define _raw_write_relax(lock) cpu_relax() + #endif /* __ASM_SPINLOCK_H */ diff --git a/include/asm-cris/arch-v32/spinlock.h b/include/asm-cris/arch-v32/spinlock.h index 52df72a622329..5f43df0a5fb42 100644 --- a/include/asm-cris/arch-v32/spinlock.h +++ b/include/asm-cris/arch-v32/spinlock.h @@ -160,4 +160,8 @@ static __inline__ int is_write_locked(rwlock_t *rw) return rw->counter < 0; } +#define _raw_spin_relax(lock) cpu_relax() +#define _raw_read_relax(lock) cpu_relax() +#define _raw_write_relax(lock) cpu_relax() + #endif /* __ASM_ARCH_SPINLOCK_H */ diff --git a/include/asm-i386/spinlock.h b/include/asm-i386/spinlock.h index b0b3043f05e15..c18b71fae6b38 100644 --- a/include/asm-i386/spinlock.h +++ b/include/asm-i386/spinlock.h @@ -205,4 +205,8 @@ static inline void __raw_write_unlock(raw_rwlock_t *rw) : "+m" (rw->lock) : : "memory"); } +#define _raw_spin_relax(lock) cpu_relax() +#define _raw_read_relax(lock) cpu_relax() +#define _raw_write_relax(lock) cpu_relax() + #endif /* __ASM_SPINLOCK_H */ diff --git a/include/asm-ia64/spinlock.h b/include/asm-ia64/spinlock.h index 9e83210dc3125..ff857e31738a0 100644 --- a/include/asm-ia64/spinlock.h +++ b/include/asm-ia64/spinlock.h @@ -213,4 +213,8 @@ static inline int __raw_read_trylock(raw_rwlock_t *x) return (u32)ia64_cmpxchg4_acq((__u32 *)(x), new.word, old.word) == old.word; } +#define _raw_spin_relax(lock) cpu_relax() +#define _raw_read_relax(lock) cpu_relax() +#define _raw_write_relax(lock) cpu_relax() + #endif /* _ASM_IA64_SPINLOCK_H */ diff --git a/include/asm-m32r/spinlock.h b/include/asm-m32r/spinlock.h index f9f90727a4a1f..f5cfba81ee10c 100644 --- a/include/asm-m32r/spinlock.h +++ b/include/asm-m32r/spinlock.h @@ -316,4 +316,8 @@ static inline int __raw_write_trylock(raw_rwlock_t *lock) return 0; } +#define _raw_spin_relax(lock) cpu_relax() +#define _raw_read_relax(lock) cpu_relax() +#define _raw_write_relax(lock) cpu_relax() + #endif /* _ASM_M32R_SPINLOCK_H */ diff --git a/include/asm-mips/spinlock.h b/include/asm-mips/spinlock.h index 4c1a1b53aeaf1..c8d5587467bbf 100644 --- a/include/asm-mips/spinlock.h +++ b/include/asm-mips/spinlock.h @@ -328,4 +328,8 @@ static inline int __raw_write_trylock(raw_rwlock_t *rw) } +#define _raw_spin_relax(lock) cpu_relax() +#define _raw_read_relax(lock) cpu_relax() +#define _raw_write_relax(lock) cpu_relax() + #endif /* _ASM_SPINLOCK_H */ diff --git a/include/asm-parisc/spinlock.h b/include/asm-parisc/spinlock.h index a93960e232cff..e1825530365d3 100644 --- a/include/asm-parisc/spinlock.h +++ b/include/asm-parisc/spinlock.h @@ -152,4 +152,8 @@ static __inline__ int __raw_write_can_lock(raw_rwlock_t *rw) return !rw->counter; } +#define _raw_spin_relax(lock) cpu_relax() +#define _raw_read_relax(lock) cpu_relax() +#define _raw_write_relax(lock) cpu_relax() + #endif /* __ASM_SPINLOCK_H */ diff --git a/include/asm-powerpc/spinlock.h b/include/asm-powerpc/spinlock.h index c31e4382a7759..eaccac8327f2d 100644 --- a/include/asm-powerpc/spinlock.h +++ b/include/asm-powerpc/spinlock.h @@ -285,5 +285,9 @@ static __inline__ void __raw_write_unlock(raw_rwlock_t *rw) rw->lock = 0; } +#define _raw_spin_relax(lock) cpu_relax() +#define _raw_read_relax(lock) cpu_relax() +#define _raw_write_relax(lock) cpu_relax() + #endif /* __KERNEL__ */ #endif /* __ASM_SPINLOCK_H */ diff --git a/include/asm-ppc/spinlock.h b/include/asm-ppc/spinlock.h index 5c64b75f0295b..fccaf5531e579 100644 --- a/include/asm-ppc/spinlock.h +++ b/include/asm-ppc/spinlock.h @@ -161,4 +161,8 @@ static __inline__ void __raw_write_unlock(raw_rwlock_t *rw) rw->lock = 0; } +#define _raw_spin_relax(lock) cpu_relax() +#define _raw_read_relax(lock) cpu_relax() +#define _raw_write_relax(lock) cpu_relax() + #endif /* __ASM_SPINLOCK_H */ diff --git a/include/asm-s390/spinlock.h b/include/asm-s390/spinlock.h index ce3edf6d63b3b..5f00feaf1be62 100644 --- a/include/asm-s390/spinlock.h +++ b/include/asm-s390/spinlock.h @@ -154,4 +154,8 @@ static inline int __raw_write_trylock(raw_rwlock_t *rw) return _raw_write_trylock_retry(rw); } +#define _raw_spin_relax(lock) cpu_relax() +#define _raw_read_relax(lock) cpu_relax() +#define _raw_write_relax(lock) cpu_relax() + #endif /* __ASM_SPINLOCK_H */ diff --git a/include/asm-sh/spinlock.h b/include/asm-sh/spinlock.h index 846322d4c35d4..54458fd249815 100644 --- a/include/asm-sh/spinlock.h +++ b/include/asm-sh/spinlock.h @@ -100,4 +100,8 @@ static inline int __raw_write_trylock(raw_rwlock_t *rw) return 0; } +#define _raw_spin_relax(lock) cpu_relax() +#define _raw_read_relax(lock) cpu_relax() +#define _raw_write_relax(lock) cpu_relax() + #endif /* __ASM_SH_SPINLOCK_H */ diff --git a/include/asm-sparc/spinlock.h b/include/asm-sparc/spinlock.h index 1c75474ba1df7..557d08959d2f3 100644 --- a/include/asm-sparc/spinlock.h +++ b/include/asm-sparc/spinlock.h @@ -154,6 +154,10 @@ static inline int __raw_write_trylock(raw_rwlock_t *rw) #define __raw_spin_lock_flags(lock, flags) __raw_spin_lock(lock) #define __raw_read_trylock(lock) generic__raw_read_trylock(lock) +#define _raw_spin_relax(lock) cpu_relax() +#define _raw_read_relax(lock) cpu_relax() +#define _raw_write_relax(lock) cpu_relax() + #define __raw_read_can_lock(rw) (!((rw)->lock & 0xff)) #define __raw_write_can_lock(rw) (!(rw)->lock) diff --git a/include/asm-sparc64/spinlock.h b/include/asm-sparc64/spinlock.h index bd5ffc76bc7e6..0006fe9f8c7a0 100644 --- a/include/asm-sparc64/spinlock.h +++ b/include/asm-sparc64/spinlock.h @@ -241,6 +241,10 @@ static int inline __write_trylock(raw_rwlock_t *lock) #define __raw_read_can_lock(rw) (!((rw)->lock & 0x80000000UL)) #define __raw_write_can_lock(rw) (!(rw)->lock) +#define _raw_spin_relax(lock) cpu_relax() +#define _raw_read_relax(lock) cpu_relax() +#define _raw_write_relax(lock) cpu_relax() + #endif /* !(__ASSEMBLY__) */ #endif /* !(__SPARC64_SPINLOCK_H) */ diff --git a/include/asm-x86_64/spinlock.h b/include/asm-x86_64/spinlock.h index 3daf5b0059054..05ef097ba55b2 100644 --- a/include/asm-x86_64/spinlock.h +++ b/include/asm-x86_64/spinlock.h @@ -133,4 +133,8 @@ static inline void __raw_write_unlock(raw_rwlock_t *rw) : "=m" (rw->lock) : : "memory"); } +#define _raw_spin_relax(lock) cpu_relax() +#define _raw_read_relax(lock) cpu_relax() +#define _raw_write_relax(lock) cpu_relax() + #endif /* __ASM_SPINLOCK_H */ diff --git a/kernel/spinlock.c b/kernel/spinlock.c index d48143eafbfde..476c3741511b3 100644 --- a/kernel/spinlock.c +++ b/kernel/spinlock.c @@ -215,7 +215,7 @@ void __lockfunc _##op##_lock(locktype##_t *lock) \ if (!(lock)->break_lock) \ (lock)->break_lock = 1; \ while (!op##_can_lock(lock) && (lock)->break_lock) \ - cpu_relax(); \ + _raw_##op##_relax(&lock->raw_lock); \ } \ (lock)->break_lock = 0; \ } \ @@ -237,7 +237,7 @@ unsigned long __lockfunc _##op##_lock_irqsave(locktype##_t *lock) \ if (!(lock)->break_lock) \ (lock)->break_lock = 1; \ while (!op##_can_lock(lock) && (lock)->break_lock) \ - cpu_relax(); \ + _raw_##op##_relax(&lock->raw_lock); \ } \ (lock)->break_lock = 0; \ return flags; \