| Message ID | 20130601192138.5966.62276.sendpatchset@codeblue (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 06/01/2013 12:21 PM, Raghavendra K T wrote: > x86/spinlock: Replace pv spinlocks with pv ticketlocks > > From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> I'm not sure what the etiquette is here; I did the work while at Citrix, but jeremy@goop.org is my canonical email address. The Citrix address is dead and bounces, so is useless for anything. Probably best to change it. J > > Rather than outright replacing the entire spinlock implementation in > order to paravirtualize it, keep the ticket lock implementation but add > a couple of pvops hooks on the slow patch (long spin on lock, unlocking > a contended lock). > > Ticket locks have a number of nice properties, but they also have some > surprising behaviours in virtual environments. They enforce a strict > FIFO ordering on cpus trying to take a lock; however, if the hypervisor > scheduler does not schedule the cpus in the correct order, the system can > waste a huge amount of time spinning until the next cpu can take the lock. > > (See Thomas Friebel's talk "Prevent Guests from Spinning Around" > http://www.xen.org/files/xensummitboston08/LHP.pdf for more details.) > > To address this, we add two hooks: > - __ticket_spin_lock which is called after the cpu has been > spinning on the lock for a significant number of iterations but has > failed to take the lock (presumably because the cpu holding the lock > has been descheduled). The lock_spinning pvop is expected to block > the cpu until it has been kicked by the current lock holder. > - __ticket_spin_unlock, which on releasing a contended lock > (there are more cpus with tail tickets), it looks to see if the next > cpu is blocked and wakes it if so. > > When compiled with CONFIG_PARAVIRT_SPINLOCKS disabled, a set of stub > functions causes all the extra code to go away. > > Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> > Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> > Tested-by: Attilio Rao <attilio.rao@citrix.com> > [ Raghavendra: Changed SPIN_THRESHOLD ] > Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com> > --- > arch/x86/include/asm/paravirt.h | 32 ++++---------------- > arch/x86/include/asm/paravirt_types.h | 10 ++---- > arch/x86/include/asm/spinlock.h | 53 +++++++++++++++++++++++++++------ > arch/x86/include/asm/spinlock_types.h | 4 -- > arch/x86/kernel/paravirt-spinlocks.c | 15 +-------- > arch/x86/xen/spinlock.c | 8 ++++- > 6 files changed, 61 insertions(+), 61 deletions(-) > > diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h > index cfdc9ee..040e72d 100644 > --- a/arch/x86/include/asm/paravirt.h > +++ b/arch/x86/include/asm/paravirt.h > @@ -712,36 +712,16 @@ static inline void __set_fixmap(unsigned /* enum fixed_addresses */ idx, > > #if defined(CONFIG_SMP) && defined(CONFIG_PARAVIRT_SPINLOCKS) > > -static inline int arch_spin_is_locked(struct arch_spinlock *lock) > +static __always_inline void __ticket_lock_spinning(struct arch_spinlock *lock, > + __ticket_t ticket) > { > - return PVOP_CALL1(int, pv_lock_ops.spin_is_locked, lock); > + PVOP_VCALL2(pv_lock_ops.lock_spinning, lock, ticket); > } > > -static inline int arch_spin_is_contended(struct arch_spinlock *lock) > +static __always_inline void ____ticket_unlock_kick(struct arch_spinlock *lock, > + __ticket_t ticket) > { > - return PVOP_CALL1(int, pv_lock_ops.spin_is_contended, lock); > -} > -#define arch_spin_is_contended arch_spin_is_contended > - > -static __always_inline void arch_spin_lock(struct arch_spinlock *lock) > -{ > - PVOP_VCALL1(pv_lock_ops.spin_lock, lock); > -} > - > -static __always_inline void arch_spin_lock_flags(struct arch_spinlock *lock, > - unsigned long flags) > -{ > - PVOP_VCALL2(pv_lock_ops.spin_lock_flags, lock, flags); > -} > - > -static __always_inline int arch_spin_trylock(struct arch_spinlock *lock) > -{ > - return PVOP_CALL1(int, pv_lock_ops.spin_trylock, lock); > -} > - > -static __always_inline void arch_spin_unlock(struct arch_spinlock *lock) > -{ > - PVOP_VCALL1(pv_lock_ops.spin_unlock, lock); > + PVOP_VCALL2(pv_lock_ops.unlock_kick, lock, ticket); > } > > #endif > diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h > index 0db1fca..d5deb6d 100644 > --- a/arch/x86/include/asm/paravirt_types.h > +++ b/arch/x86/include/asm/paravirt_types.h > @@ -327,13 +327,11 @@ struct pv_mmu_ops { > }; > > struct arch_spinlock; > +#include <asm/spinlock_types.h> > + > struct pv_lock_ops { > - int (*spin_is_locked)(struct arch_spinlock *lock); > - int (*spin_is_contended)(struct arch_spinlock *lock); > - void (*spin_lock)(struct arch_spinlock *lock); > - void (*spin_lock_flags)(struct arch_spinlock *lock, unsigned long flags); > - int (*spin_trylock)(struct arch_spinlock *lock); > - void (*spin_unlock)(struct arch_spinlock *lock); > + void (*lock_spinning)(struct arch_spinlock *lock, __ticket_t ticket); > + void (*unlock_kick)(struct arch_spinlock *lock, __ticket_t ticket); > }; > > /* This contains all the paravirt structures: we get a convenient > diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h > index 33692ea..4d54244 100644 > --- a/arch/x86/include/asm/spinlock.h > +++ b/arch/x86/include/asm/spinlock.h > @@ -34,6 +34,35 @@ > # define UNLOCK_LOCK_PREFIX > #endif > > +/* How long a lock should spin before we consider blocking */ > +#define SPIN_THRESHOLD (1 << 15) > + > +#ifndef CONFIG_PARAVIRT_SPINLOCKS > + > +static __always_inline void __ticket_lock_spinning(struct arch_spinlock *lock, > + __ticket_t ticket) > +{ > +} > + > +static __always_inline void ____ticket_unlock_kick(struct arch_spinlock *lock, > + __ticket_t ticket) > +{ > +} > + > +#endif /* CONFIG_PARAVIRT_SPINLOCKS */ > + > + > +/* > + * If a spinlock has someone waiting on it, then kick the appropriate > + * waiting cpu. > + */ > +static __always_inline void __ticket_unlock_kick(struct arch_spinlock *lock, > + __ticket_t next) > +{ > + if (unlikely(lock->tickets.tail != next)) > + ____ticket_unlock_kick(lock, next); > +} > + > /* > * Ticket locks are conceptually two parts, one indicating the current head of > * the queue, and the other indicating the current tail. The lock is acquired > @@ -47,19 +76,24 @@ > * in the high part, because a wide xadd increment of the low part would carry > * up and contaminate the high part. > */ > -static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock) > +static __always_inline void __ticket_spin_lock(struct arch_spinlock *lock) > { > register struct __raw_tickets inc = { .tail = 1 }; > > inc = xadd(&lock->tickets, inc); > > for (;;) { > - if (inc.head == inc.tail) > - break; > - cpu_relax(); > - inc.head = ACCESS_ONCE(lock->tickets.head); > + unsigned count = SPIN_THRESHOLD; > + > + do { > + if (inc.head == inc.tail) > + goto out; > + cpu_relax(); > + inc.head = ACCESS_ONCE(lock->tickets.head); > + } while (--count); > + __ticket_lock_spinning(lock, inc.tail); > } > - barrier(); /* make sure nothing creeps before the lock is taken */ > +out: barrier(); /* make sure nothing creeps before the lock is taken */ > } > > static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock) > @@ -78,7 +112,10 @@ static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock) > > static __always_inline void __ticket_spin_unlock(arch_spinlock_t *lock) > { > + __ticket_t next = lock->tickets.head + 1; > + > __add(&lock->tickets.head, 1, UNLOCK_LOCK_PREFIX); > + __ticket_unlock_kick(lock, next); > } > > static inline int __ticket_spin_is_locked(arch_spinlock_t *lock) > @@ -95,8 +132,6 @@ static inline int __ticket_spin_is_contended(arch_spinlock_t *lock) > return (__ticket_t)(tmp.tail - tmp.head) > 1; > } > > -#ifndef CONFIG_PARAVIRT_SPINLOCKS > - > static inline int arch_spin_is_locked(arch_spinlock_t *lock) > { > return __ticket_spin_is_locked(lock); > @@ -129,8 +164,6 @@ static __always_inline void arch_spin_lock_flags(arch_spinlock_t *lock, > arch_spin_lock(lock); > } > > -#endif /* CONFIG_PARAVIRT_SPINLOCKS */ > - > static inline void arch_spin_unlock_wait(arch_spinlock_t *lock) > { > while (arch_spin_is_locked(lock)) > diff --git a/arch/x86/include/asm/spinlock_types.h b/arch/x86/include/asm/spinlock_types.h > index ad0ad07..83fd3c7 100644 > --- a/arch/x86/include/asm/spinlock_types.h > +++ b/arch/x86/include/asm/spinlock_types.h > @@ -1,10 +1,6 @@ > #ifndef _ASM_X86_SPINLOCK_TYPES_H > #define _ASM_X86_SPINLOCK_TYPES_H > > -#ifndef __LINUX_SPINLOCK_TYPES_H > -# error "please don't include this file directly" > -#endif > - > #include <linux/types.h> > > #if (CONFIG_NR_CPUS < 256) > diff --git a/arch/x86/kernel/paravirt-spinlocks.c b/arch/x86/kernel/paravirt-spinlocks.c > index 676b8c7..c2e010e 100644 > --- a/arch/x86/kernel/paravirt-spinlocks.c > +++ b/arch/x86/kernel/paravirt-spinlocks.c > @@ -7,21 +7,10 @@ > > #include <asm/paravirt.h> > > -static inline void > -default_spin_lock_flags(arch_spinlock_t *lock, unsigned long flags) > -{ > - arch_spin_lock(lock); > -} > - > struct pv_lock_ops pv_lock_ops = { > #ifdef CONFIG_SMP > - .spin_is_locked = __ticket_spin_is_locked, > - .spin_is_contended = __ticket_spin_is_contended, > - > - .spin_lock = __ticket_spin_lock, > - .spin_lock_flags = default_spin_lock_flags, > - .spin_trylock = __ticket_spin_trylock, > - .spin_unlock = __ticket_spin_unlock, > + .lock_spinning = paravirt_nop, > + .unlock_kick = paravirt_nop, > #endif > }; > EXPORT_SYMBOL(pv_lock_ops); > diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c > index 3002ec1..d6481a9 100644 > --- a/arch/x86/xen/spinlock.c > +++ b/arch/x86/xen/spinlock.c > @@ -138,6 +138,9 @@ struct xen_spinlock { > xen_spinners_t spinners; /* count of waiting cpus */ > }; > > +static DEFINE_PER_CPU(int, lock_kicker_irq) = -1; > + > +#if 0 > static int xen_spin_is_locked(struct arch_spinlock *lock) > { > struct xen_spinlock *xl = (struct xen_spinlock *)lock; > @@ -165,7 +168,6 @@ static int xen_spin_trylock(struct arch_spinlock *lock) > return old == 0; > } > > -static DEFINE_PER_CPU(int, lock_kicker_irq) = -1; > static DEFINE_PER_CPU(struct xen_spinlock *, lock_spinners); > > /* > @@ -352,6 +354,7 @@ static void xen_spin_unlock(struct arch_spinlock *lock) > if (unlikely(xl->spinners)) > xen_spin_unlock_slow(xl); > } > +#endif > > static irqreturn_t dummy_handler(int irq, void *dev_id) > { > @@ -413,13 +416,14 @@ void __init xen_init_spinlocks(void) > return; > > BUILD_BUG_ON(sizeof(struct xen_spinlock) > sizeof(arch_spinlock_t)); > - > +#if 0 > pv_lock_ops.spin_is_locked = xen_spin_is_locked; > pv_lock_ops.spin_is_contended = xen_spin_is_contended; > pv_lock_ops.spin_lock = xen_spin_lock; > pv_lock_ops.spin_lock_flags = xen_spin_lock_flags; > pv_lock_ops.spin_trylock = xen_spin_trylock; > pv_lock_ops.spin_unlock = xen_spin_unlock; > +#endif > } > > #ifdef CONFIG_XEN_DEBUG_FS > -- 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
On 06/02/2013 02:02 AM, Jeremy Fitzhardinge wrote: > On 06/01/2013 12:21 PM, Raghavendra K T wrote: >> x86/spinlock: Replace pv spinlocks with pv ticketlocks >> >> From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> > I'm not sure what the etiquette is here; I did the work while at Citrix, > but jeremy@goop.org is my canonical email address. The Citrix address > is dead and bounces, so is useless for anything. Probably best to > change it. > Agreed. I would change to goop address in the next posting. I had the same doubt for Vatsa's email also. Even I am not sure about the practice here. So had kept as is. -- 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/paravirt.h b/arch/x86/include/asm/paravirt.h index cfdc9ee..040e72d 100644 --- a/arch/x86/include/asm/paravirt.h +++ b/arch/x86/include/asm/paravirt.h @@ -712,36 +712,16 @@ static inline void __set_fixmap(unsigned /* enum fixed_addresses */ idx, #if defined(CONFIG_SMP) && defined(CONFIG_PARAVIRT_SPINLOCKS) -static inline int arch_spin_is_locked(struct arch_spinlock *lock) +static __always_inline void __ticket_lock_spinning(struct arch_spinlock *lock, + __ticket_t ticket) { - return PVOP_CALL1(int, pv_lock_ops.spin_is_locked, lock); + PVOP_VCALL2(pv_lock_ops.lock_spinning, lock, ticket); } -static inline int arch_spin_is_contended(struct arch_spinlock *lock) +static __always_inline void ____ticket_unlock_kick(struct arch_spinlock *lock, + __ticket_t ticket) { - return PVOP_CALL1(int, pv_lock_ops.spin_is_contended, lock); -} -#define arch_spin_is_contended arch_spin_is_contended - -static __always_inline void arch_spin_lock(struct arch_spinlock *lock) -{ - PVOP_VCALL1(pv_lock_ops.spin_lock, lock); -} - -static __always_inline void arch_spin_lock_flags(struct arch_spinlock *lock, - unsigned long flags) -{ - PVOP_VCALL2(pv_lock_ops.spin_lock_flags, lock, flags); -} - -static __always_inline int arch_spin_trylock(struct arch_spinlock *lock) -{ - return PVOP_CALL1(int, pv_lock_ops.spin_trylock, lock); -} - -static __always_inline void arch_spin_unlock(struct arch_spinlock *lock) -{ - PVOP_VCALL1(pv_lock_ops.spin_unlock, lock); + PVOP_VCALL2(pv_lock_ops.unlock_kick, lock, ticket); } #endif diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h index 0db1fca..d5deb6d 100644 --- a/arch/x86/include/asm/paravirt_types.h +++ b/arch/x86/include/asm/paravirt_types.h @@ -327,13 +327,11 @@ struct pv_mmu_ops { }; struct arch_spinlock; +#include <asm/spinlock_types.h> + struct pv_lock_ops { - int (*spin_is_locked)(struct arch_spinlock *lock); - int (*spin_is_contended)(struct arch_spinlock *lock); - void (*spin_lock)(struct arch_spinlock *lock); - void (*spin_lock_flags)(struct arch_spinlock *lock, unsigned long flags); - int (*spin_trylock)(struct arch_spinlock *lock); - void (*spin_unlock)(struct arch_spinlock *lock); + void (*lock_spinning)(struct arch_spinlock *lock, __ticket_t ticket); + void (*unlock_kick)(struct arch_spinlock *lock, __ticket_t ticket); }; /* This contains all the paravirt structures: we get a convenient diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h index 33692ea..4d54244 100644 --- a/arch/x86/include/asm/spinlock.h +++ b/arch/x86/include/asm/spinlock.h @@ -34,6 +34,35 @@ # define UNLOCK_LOCK_PREFIX #endif +/* How long a lock should spin before we consider blocking */ +#define SPIN_THRESHOLD (1 << 15) + +#ifndef CONFIG_PARAVIRT_SPINLOCKS + +static __always_inline void __ticket_lock_spinning(struct arch_spinlock *lock, + __ticket_t ticket) +{ +} + +static __always_inline void ____ticket_unlock_kick(struct arch_spinlock *lock, + __ticket_t ticket) +{ +} + +#endif /* CONFIG_PARAVIRT_SPINLOCKS */ + + +/* + * If a spinlock has someone waiting on it, then kick the appropriate + * waiting cpu. + */ +static __always_inline void __ticket_unlock_kick(struct arch_spinlock *lock, + __ticket_t next) +{ + if (unlikely(lock->tickets.tail != next)) + ____ticket_unlock_kick(lock, next); +} + /* * Ticket locks are conceptually two parts, one indicating the current head of * the queue, and the other indicating the current tail. The lock is acquired @@ -47,19 +76,24 @@ * in the high part, because a wide xadd increment of the low part would carry * up and contaminate the high part. */ -static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock) +static __always_inline void __ticket_spin_lock(struct arch_spinlock *lock) { register struct __raw_tickets inc = { .tail = 1 }; inc = xadd(&lock->tickets, inc); for (;;) { - if (inc.head == inc.tail) - break; - cpu_relax(); - inc.head = ACCESS_ONCE(lock->tickets.head); + unsigned count = SPIN_THRESHOLD; + + do { + if (inc.head == inc.tail) + goto out; + cpu_relax(); + inc.head = ACCESS_ONCE(lock->tickets.head); + } while (--count); + __ticket_lock_spinning(lock, inc.tail); } - barrier(); /* make sure nothing creeps before the lock is taken */ +out: barrier(); /* make sure nothing creeps before the lock is taken */ } static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock) @@ -78,7 +112,10 @@ static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock) static __always_inline void __ticket_spin_unlock(arch_spinlock_t *lock) { + __ticket_t next = lock->tickets.head + 1; + __add(&lock->tickets.head, 1, UNLOCK_LOCK_PREFIX); + __ticket_unlock_kick(lock, next); } static inline int __ticket_spin_is_locked(arch_spinlock_t *lock) @@ -95,8 +132,6 @@ static inline int __ticket_spin_is_contended(arch_spinlock_t *lock) return (__ticket_t)(tmp.tail - tmp.head) > 1; } -#ifndef CONFIG_PARAVIRT_SPINLOCKS - static inline int arch_spin_is_locked(arch_spinlock_t *lock) { return __ticket_spin_is_locked(lock); @@ -129,8 +164,6 @@ static __always_inline void arch_spin_lock_flags(arch_spinlock_t *lock, arch_spin_lock(lock); } -#endif /* CONFIG_PARAVIRT_SPINLOCKS */ - static inline void arch_spin_unlock_wait(arch_spinlock_t *lock) { while (arch_spin_is_locked(lock)) diff --git a/arch/x86/include/asm/spinlock_types.h b/arch/x86/include/asm/spinlock_types.h index ad0ad07..83fd3c7 100644 --- a/arch/x86/include/asm/spinlock_types.h +++ b/arch/x86/include/asm/spinlock_types.h @@ -1,10 +1,6 @@ #ifndef _ASM_X86_SPINLOCK_TYPES_H #define _ASM_X86_SPINLOCK_TYPES_H -#ifndef __LINUX_SPINLOCK_TYPES_H -# error "please don't include this file directly" -#endif - #include <linux/types.h> #if (CONFIG_NR_CPUS < 256) diff --git a/arch/x86/kernel/paravirt-spinlocks.c b/arch/x86/kernel/paravirt-spinlocks.c index 676b8c7..c2e010e 100644 --- a/arch/x86/kernel/paravirt-spinlocks.c +++ b/arch/x86/kernel/paravirt-spinlocks.c @@ -7,21 +7,10 @@ #include <asm/paravirt.h> -static inline void -default_spin_lock_flags(arch_spinlock_t *lock, unsigned long flags) -{ - arch_spin_lock(lock); -} - struct pv_lock_ops pv_lock_ops = { #ifdef CONFIG_SMP - .spin_is_locked = __ticket_spin_is_locked, - .spin_is_contended = __ticket_spin_is_contended, - - .spin_lock = __ticket_spin_lock, - .spin_lock_flags = default_spin_lock_flags, - .spin_trylock = __ticket_spin_trylock, - .spin_unlock = __ticket_spin_unlock, + .lock_spinning = paravirt_nop, + .unlock_kick = paravirt_nop, #endif }; EXPORT_SYMBOL(pv_lock_ops); diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c index 3002ec1..d6481a9 100644 --- a/arch/x86/xen/spinlock.c +++ b/arch/x86/xen/spinlock.c @@ -138,6 +138,9 @@ struct xen_spinlock { xen_spinners_t spinners; /* count of waiting cpus */ }; +static DEFINE_PER_CPU(int, lock_kicker_irq) = -1; + +#if 0 static int xen_spin_is_locked(struct arch_spinlock *lock) { struct xen_spinlock *xl = (struct xen_spinlock *)lock; @@ -165,7 +168,6 @@ static int xen_spin_trylock(struct arch_spinlock *lock) return old == 0; } -static DEFINE_PER_CPU(int, lock_kicker_irq) = -1; static DEFINE_PER_CPU(struct xen_spinlock *, lock_spinners); /* @@ -352,6 +354,7 @@ static void xen_spin_unlock(struct arch_spinlock *lock) if (unlikely(xl->spinners)) xen_spin_unlock_slow(xl); } +#endif static irqreturn_t dummy_handler(int irq, void *dev_id) { @@ -413,13 +416,14 @@ void __init xen_init_spinlocks(void) return; BUILD_BUG_ON(sizeof(struct xen_spinlock) > sizeof(arch_spinlock_t)); - +#if 0 pv_lock_ops.spin_is_locked = xen_spin_is_locked; pv_lock_ops.spin_is_contended = xen_spin_is_contended; pv_lock_ops.spin_lock = xen_spin_lock; pv_lock_ops.spin_lock_flags = xen_spin_lock_flags; pv_lock_ops.spin_trylock = xen_spin_trylock; pv_lock_ops.spin_unlock = xen_spin_unlock; +#endif } #ifdef CONFIG_XEN_DEBUG_FS