From ef6edc9746dc2bfdacf44eefd5f881179971c478 Mon Sep 17 00:00:00 2001 From: Martin Schwidefsky Date: Sat, 30 Sep 2006 23:27:43 -0700 Subject: [PATCH] [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 --- include/asm-alpha/spinlock.h | 4 ++++ include/asm-arm/spinlock.h | 4 ++++ include/asm-cris/arch-v32/spinlock.h | 4 ++++ include/asm-i386/spinlock.h | 4 ++++ include/asm-ia64/spinlock.h | 4 ++++ include/asm-m32r/spinlock.h | 4 ++++ include/asm-mips/spinlock.h | 4 ++++ include/asm-parisc/spinlock.h | 4 ++++ include/asm-powerpc/spinlock.h | 4 ++++ include/asm-ppc/spinlock.h | 4 ++++ include/asm-s390/spinlock.h | 4 ++++ include/asm-sh/spinlock.h | 4 ++++ include/asm-sparc/spinlock.h | 4 ++++ include/asm-sparc64/spinlock.h | 4 ++++ include/asm-x86_64/spinlock.h | 4 ++++ kernel/spinlock.c | 4 ++-- 16 files changed, 62 insertions(+), 2 deletions(-) diff --git a/include/asm-alpha/spinlock.h b/include/asm-alpha/spinlock.h index 0c294c9b0c..aeeb125f68 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 01b7c26a30..861092fbaa 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 52df72a622..5f43df0a5f 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 b0b3043f05..c18b71fae6 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 9e83210dc3..ff857e3173 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 f9f90727a4..f5cfba81ee 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 4c1a1b53ae..c8d5587467 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 a93960e232..e182553036 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 c31e4382a7..eaccac8327 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 5c64b75f02..fccaf5531e 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 ce3edf6d63..5f00feaf1b 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 846322d4c3..54458fd249 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 1c75474ba1..557d08959d 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 bd5ffc76bc..0006fe9f8c 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 3daf5b0059..05ef097ba5 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 d48143eafb..476c374151 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; \ -- 2.39.5