diff options
| author | Jeremy Fitzhardinge <jeremy@goop.org> | 2010-11-15 14:40:47 -0800 |
|---|---|---|
| committer | Jeremy Fitzhardinge <jeremy@goop.org> | 2011-11-25 10:46:57 -0800 |
| commit | 30d7775245d478ec071c4974ff5eb72c1a4f5d51 (patch) | |
| tree | 81a78e2978dd628537be7addcf1aed309e157b73 | |
| parent | 5738ffb03354c54ef41f87fe1a34309a80c5b337 (diff) | |
| download | xen-30d7775245d478ec071c4974ff5eb72c1a4f5d51.tar.gz | |
x86/pvticketlock: when paravirtualizing ticket locks, increment by 2
Increment ticket head/tails by 2 rather than 1 to leave the LSB free
to store a "is in slowpath state" bit. This halves the number
of possible CPUs for a given ticket size, but this shouldn't matter
in practice - kernels built for 32k+ CPU systems are probably
specially built for the hardware rather than a generic distro
kernel.
Signed-off-by: Jeremy Fitzhardinge <jeremy@goop.org>
| -rw-r--r-- | arch/x86/include/asm/spinlock.h | 10 | ||||
| -rw-r--r-- | arch/x86/include/asm/spinlock_types.h | 10 |
2 files changed, 14 insertions, 6 deletions
diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h index f0d6a59479c60d..dd155f7436c4e7 100644 --- a/arch/x86/include/asm/spinlock.h +++ b/arch/x86/include/asm/spinlock.h @@ -78,7 +78,7 @@ static __always_inline void __ticket_unlock_kick(struct arch_spinlock *lock, __t */ static __always_inline void arch_spin_lock(struct arch_spinlock *lock) { - register struct __raw_tickets inc = { .tail = 1 }; + register struct __raw_tickets inc = { .tail = TICKET_LOCK_INC }; inc = xadd(&lock->tickets, inc); @@ -104,7 +104,7 @@ static __always_inline int arch_spin_trylock(arch_spinlock_t *lock) if (old.tickets.head != old.tickets.tail) return 0; - new.head_tail = old.head_tail + (1 << TICKET_SHIFT); + new.head_tail = old.head_tail + (TICKET_LOCK_INC << TICKET_SHIFT); /* cmpxchg is a full barrier, so nothing can move before it */ return cmpxchg(&lock->head_tail, old.head_tail, new.head_tail) == old.head_tail; @@ -112,9 +112,9 @@ static __always_inline int arch_spin_trylock(arch_spinlock_t *lock) static __always_inline void arch_spin_unlock(arch_spinlock_t *lock) { - __ticket_t next = lock->tickets.head + 1; + __ticket_t next = lock->tickets.head + TICKET_LOCK_INC; - __add(&lock->tickets.head, 1, UNLOCK_LOCK_PREFIX); + __add(&lock->tickets.head, TICKET_LOCK_INC, UNLOCK_LOCK_PREFIX); __ticket_unlock_kick(lock, next); } @@ -129,7 +129,7 @@ static inline int arch_spin_is_contended(arch_spinlock_t *lock) { struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets); - return ((tmp.tail - tmp.head) & TICKET_MASK) > 1; + return ((tmp.tail - tmp.head) & TICKET_MASK) > TICKET_LOCK_INC; } #define arch_spin_is_contended arch_spin_is_contended diff --git a/arch/x86/include/asm/spinlock_types.h b/arch/x86/include/asm/spinlock_types.h index dbe223d9ca9fb7..aa9a205b19b81f 100644 --- a/arch/x86/include/asm/spinlock_types.h +++ b/arch/x86/include/asm/spinlock_types.h @@ -3,7 +3,13 @@ #include <linux/types.h> -#if (CONFIG_NR_CPUS < 256) +#ifdef CONFIG_PARAVIRT_SPINLOCKS +#define __TICKET_LOCK_INC 2 +#else +#define __TICKET_LOCK_INC 1 +#endif + +#if (CONFIG_NR_CPUS < (256 / __TICKET_LOCK_INC)) typedef u8 __ticket_t; typedef u16 __ticketpair_t; #else @@ -11,6 +17,8 @@ typedef u16 __ticket_t; typedef u32 __ticketpair_t; #endif +#define TICKET_LOCK_INC ((__ticket_t)__TICKET_LOCK_INC) + #define TICKET_SHIFT (sizeof(__ticket_t) * 8) #define TICKET_MASK ((__ticket_t)((1 << TICKET_SHIFT) - 1)) |