| Message ID | 20130601192402.5966.4600.sendpatchset@codeblue (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Sun, Jun 02, 2013 at 12:54:02AM +0530, Raghavendra K T wrote: > x86/pvticketlock: When paravirtualizing ticket locks, increment by 2 > > From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> > > 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.fitzhardinge@citrix.com> > Tested-by: Attilio Rao <attilio.rao@citrix.com> > Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> > --- > arch/x86/include/asm/spinlock.h | 10 +++++----- > 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 7442410..04a5cd5 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, > */ > 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 (__ticket_t)(tmp.tail - tmp.head) > 1; > + return (__ticket_t)(tmp.tail - tmp.head) > 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 83fd3c7..e96fcbd 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) > > typedef struct arch_spinlock { > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h index 7442410..04a5cd5 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, */ 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 (__ticket_t)(tmp.tail - tmp.head) > 1; + return (__ticket_t)(tmp.tail - tmp.head) > 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 83fd3c7..e96fcbd 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) typedef struct arch_spinlock {