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x86, locking/spinlocks: Remove ticket (spin)lock implementation 

We've unconditionally used the queued spinlock for many releases now.

Its time to remove the old ticket lock code.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <waiman.long@hpe.com>
Cc: Waiman.Long@hpe.com
Cc: david.vrabel@citrix.com
Cc: dhowells@redhat.com
Cc: pbonzini@redhat.com
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/20160518184302.GO3193@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2016-05-18 20:43:02 +02:00 committed by Ingo Molnar
parent 0b429e18c2
commit cfd8983f03
10 changed files with 6 additions and 719 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
arch/x86/Kconfig
View File

@ -705,7 +705,6 @@ config PARAVIRT_DEBUG
config PARAVIRT_SPINLOCKS
bool "Paravirtualization layer for spinlocks"
depends on PARAVIRT && SMP
select UNINLINE_SPIN_UNLOCK if !QUEUED_SPINLOCKS
---help---
Paravirtualized spinlocks allow a pvops backend to replace the
spinlock implementation with something virtualization-friendly
@ -718,7 +717,7 @@ config PARAVIRT_SPINLOCKS
config QUEUED_LOCK_STAT
bool "Paravirt queued spinlock statistics"
depends on PARAVIRT_SPINLOCKS && DEBUG_FS && QUEUED_SPINLOCKS
depends on PARAVIRT_SPINLOCKS && DEBUG_FS
---help---
Enable the collection of statistical data on the slowpath
behavior of paravirtualized queued spinlocks and report

18
arch/x86/include/asm/paravirt.h
View File

@ -661,8 +661,6 @@ static inline void __set_fixmap(unsigned /* enum fixed_addresses */ idx,
#if defined(CONFIG_SMP) && defined(CONFIG_PARAVIRT_SPINLOCKS)
#ifdef CONFIG_QUEUED_SPINLOCKS
static __always_inline void pv_queued_spin_lock_slowpath(struct qspinlock *lock,
u32 val)
{
@ -684,22 +682,6 @@ static __always_inline void pv_kick(int cpu)
PVOP_VCALL1(pv_lock_ops.kick, cpu);
}
#else /* !CONFIG_QUEUED_SPINLOCKS */
static __always_inline void __ticket_lock_spinning(struct arch_spinlock *lock,
__ticket_t ticket)
{
PVOP_VCALLEE2(pv_lock_ops.lock_spinning, lock, ticket);
}
static __always_inline void __ticket_unlock_kick(struct arch_spinlock *lock,
__ticket_t ticket)
{
PVOP_VCALL2(pv_lock_ops.unlock_kick, lock, ticket);
}
#endif /* CONFIG_QUEUED_SPINLOCKS */
#endif /* SMP && PARAVIRT_SPINLOCKS */
#ifdef CONFIG_X86_32

7
arch/x86/include/asm/paravirt_types.h
View File

@ -301,23 +301,16 @@ struct pv_mmu_ops {
struct arch_spinlock;
#ifdef CONFIG_SMP
#include <asm/spinlock_types.h>
#else
typedef u16 __ticket_t;
#endif
struct qspinlock;
struct pv_lock_ops {
#ifdef CONFIG_QUEUED_SPINLOCKS
void (*queued_spin_lock_slowpath)(struct qspinlock *lock, u32 val);
struct paravirt_callee_save queued_spin_unlock;
void (*wait)(u8 *ptr, u8 val);
void (*kick)(int cpu);
#else /* !CONFIG_QUEUED_SPINLOCKS */
struct paravirt_callee_save lock_spinning;
void (*unlock_kick)(struct arch_spinlock *lock, __ticket_t ticket);
#endif /* !CONFIG_QUEUED_SPINLOCKS */
};
/* This contains all the paravirt structures: we get a convenient

174
arch/x86/include/asm/spinlock.h
View File

@ -20,187 +20,13 @@
* (the type definitions are in asm/spinlock_types.h)
*/
#ifdef CONFIG_X86_32
# define LOCK_PTR_REG "a"
#else
# define LOCK_PTR_REG "D"
#endif
#if defined(CONFIG_X86_32) && (defined(CONFIG_X86_PPRO_FENCE))
/*
* On PPro SMP, we use a locked operation to unlock
* (PPro errata 66, 92)
*/
# define UNLOCK_LOCK_PREFIX LOCK_PREFIX
#else
# define UNLOCK_LOCK_PREFIX
#endif
/* How long a lock should spin before we consider blocking */
#define SPIN_THRESHOLD (1 << 15)
extern struct static_key paravirt_ticketlocks_enabled;
static __always_inline bool static_key_false(struct static_key *key);
#ifdef CONFIG_QUEUED_SPINLOCKS
#include <asm/qspinlock.h>
#else
#ifdef CONFIG_PARAVIRT_SPINLOCKS
static inline void __ticket_enter_slowpath(arch_spinlock_t *lock)
{
set_bit(0, (volatile unsigned long *)&lock->tickets.head);
}
#else /* !CONFIG_PARAVIRT_SPINLOCKS */
static __always_inline void __ticket_lock_spinning(arch_spinlock_t *lock,
__ticket_t ticket)
{
}
static inline void __ticket_unlock_kick(arch_spinlock_t *lock,
__ticket_t ticket)
{
}
#endif /* CONFIG_PARAVIRT_SPINLOCKS */
static inline int __tickets_equal(__ticket_t one, __ticket_t two)
{
return !((one ^ two) & ~TICKET_SLOWPATH_FLAG);
}
static inline void __ticket_check_and_clear_slowpath(arch_spinlock_t *lock,
__ticket_t head)
{
if (head & TICKET_SLOWPATH_FLAG) {
arch_spinlock_t old, new;
old.tickets.head = head;
new.tickets.head = head & ~TICKET_SLOWPATH_FLAG;
old.tickets.tail = new.tickets.head + TICKET_LOCK_INC;
new.tickets.tail = old.tickets.tail;
/* try to clear slowpath flag when there are no contenders */
cmpxchg(&lock->head_tail, old.head_tail, new.head_tail);
}
}
static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
{
return __tickets_equal(lock.tickets.head, lock.tickets.tail);
}
/*
* 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
* by atomically noting the tail and incrementing it by one (thus adding
* ourself to the queue and noting our position), then waiting until the head
* becomes equal to the the initial value of the tail.
*
* We use an xadd covering *both* parts of the lock, to increment the tail and
* also load the position of the head, which takes care of memory ordering
* issues and should be optimal for the uncontended case. Note the tail must be
* 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 arch_spin_lock(arch_spinlock_t *lock)
{
register struct __raw_tickets inc = { .tail = TICKET_LOCK_INC };
inc = xadd(&lock->tickets, inc);
if (likely(inc.head == inc.tail))
goto out;
for (;;) {
unsigned count = SPIN_THRESHOLD;
do {
inc.head = READ_ONCE(lock->tickets.head);
if (__tickets_equal(inc.head, inc.tail))
goto clear_slowpath;
cpu_relax();
} while (--count);
__ticket_lock_spinning(lock, inc.tail);
}
clear_slowpath:
__ticket_check_and_clear_slowpath(lock, inc.head);
out:
barrier(); /* make sure nothing creeps before the lock is taken */
}
static __always_inline int arch_spin_trylock(arch_spinlock_t *lock)
{
arch_spinlock_t old, new;
old.tickets = READ_ONCE(lock->tickets);
if (!__tickets_equal(old.tickets.head, old.tickets.tail))
return 0;
new.head_tail = old.head_tail + (TICKET_LOCK_INC << TICKET_SHIFT);
new.head_tail &= ~TICKET_SLOWPATH_FLAG;
/* 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;
}
static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
{
if (TICKET_SLOWPATH_FLAG &&
static_key_false(&paravirt_ticketlocks_enabled)) {
__ticket_t head;
BUILD_BUG_ON(((__ticket_t)NR_CPUS) != NR_CPUS);
head = xadd(&lock->tickets.head, TICKET_LOCK_INC);
if (unlikely(head & TICKET_SLOWPATH_FLAG)) {
head &= ~TICKET_SLOWPATH_FLAG;
__ticket_unlock_kick(lock, (head + TICKET_LOCK_INC));
}
} else
__add(&lock->tickets.head, TICKET_LOCK_INC, UNLOCK_LOCK_PREFIX);
}
static inline int arch_spin_is_locked(arch_spinlock_t *lock)
{
struct __raw_tickets tmp = READ_ONCE(lock->tickets);
return !__tickets_equal(tmp.tail, tmp.head);
}
static inline int arch_spin_is_contended(arch_spinlock_t *lock)
{
struct __raw_tickets tmp = READ_ONCE(lock->tickets);
tmp.head &= ~TICKET_SLOWPATH_FLAG;
return (__ticket_t)(tmp.tail - tmp.head) > TICKET_LOCK_INC;
}
#define arch_spin_is_contended arch_spin_is_contended
static __always_inline void arch_spin_lock_flags(arch_spinlock_t *lock,
unsigned long flags)
{
arch_spin_lock(lock);
}
static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
{
__ticket_t head = READ_ONCE(lock->tickets.head);
for (;;) {
struct __raw_tickets tmp = READ_ONCE(lock->tickets);
/*
* We need to check "unlocked" in a loop, tmp.head == head
* can be false positive because of overflow.
*/
if (__tickets_equal(tmp.head, tmp.tail) ||
!__tickets_equal(tmp.head, head))
break;
cpu_relax();
}
}
#endif /* CONFIG_QUEUED_SPINLOCKS */
/*
* Read-write spinlocks, allowing multiple readers

13
arch/x86/include/asm/spinlock_types.h
View File

@ -23,20 +23,7 @@ typedef u32 __ticketpair_t;
#define TICKET_SHIFT (sizeof(__ticket_t) * 8)
#ifdef CONFIG_QUEUED_SPINLOCKS
#include <asm-generic/qspinlock_types.h>
#else
typedef struct arch_spinlock {
union {
__ticketpair_t head_tail;
struct __raw_tickets {
__ticket_t head, tail;
} tickets;
};
} arch_spinlock_t;
#define __ARCH_SPIN_LOCK_UNLOCKED { { 0 } }
#endif /* CONFIG_QUEUED_SPINLOCKS */
#include <asm-generic/qrwlock_types.h>

245
arch/x86/kernel/kvm.c
View File

@ -575,9 +575,6 @@ static void kvm_kick_cpu(int cpu)
kvm_hypercall2(KVM_HC_KICK_CPU, flags, apicid);
}
#ifdef CONFIG_QUEUED_SPINLOCKS
#include <asm/qspinlock.h>
static void kvm_wait(u8 *ptr, u8 val)
@ -606,243 +603,6 @@ out:
local_irq_restore(flags);
}
#else /* !CONFIG_QUEUED_SPINLOCKS */
enum kvm_contention_stat {
TAKEN_SLOW,
TAKEN_SLOW_PICKUP,
RELEASED_SLOW,
RELEASED_SLOW_KICKED,
NR_CONTENTION_STATS
};
#ifdef CONFIG_KVM_DEBUG_FS
#define HISTO_BUCKETS 30
static struct kvm_spinlock_stats
{
u32 contention_stats[NR_CONTENTION_STATS];
u32 histo_spin_blocked[HISTO_BUCKETS+1];
u64 time_blocked;
} spinlock_stats;
static u8 zero_stats;
static inline void check_zero(void)
{
u8 ret;
u8 old;
old = READ_ONCE(zero_stats);
if (unlikely(old)) {
ret = cmpxchg(&zero_stats, old, 0);
/* This ensures only one fellow resets the stat */
if (ret == old)
memset(&spinlock_stats, 0, sizeof(spinlock_stats));
}
}
static inline void add_stats(enum kvm_contention_stat var, u32 val)
{
check_zero();
spinlock_stats.contention_stats[var] += val;
}
static inline u64 spin_time_start(void)
{
return sched_clock();
}
static void __spin_time_accum(u64 delta, u32 *array)
{
unsigned index;
index = ilog2(delta);
check_zero();
if (index < HISTO_BUCKETS)
array[index]++;
else
array[HISTO_BUCKETS]++;
}
static inline void spin_time_accum_blocked(u64 start)
{
u32 delta;
delta = sched_clock() - start;
__spin_time_accum(delta, spinlock_stats.histo_spin_blocked);
spinlock_stats.time_blocked += delta;
}
static struct dentry *d_spin_debug;
static struct dentry *d_kvm_debug;
static struct dentry *kvm_init_debugfs(void)
{
d_kvm_debug = debugfs_create_dir("kvm-guest", NULL);
if (!d_kvm_debug)
printk(KERN_WARNING "Could not create 'kvm' debugfs directory\n");
return d_kvm_debug;
}
static int __init kvm_spinlock_debugfs(void)
{
struct dentry *d_kvm;
d_kvm = kvm_init_debugfs();
if (d_kvm == NULL)
return -ENOMEM;
d_spin_debug = debugfs_create_dir("spinlocks", d_kvm);
debugfs_create_u8("zero_stats", 0644, d_spin_debug, &zero_stats);
debugfs_create_u32("taken_slow", 0444, d_spin_debug,
&spinlock_stats.contention_stats[TAKEN_SLOW]);
debugfs_create_u32("taken_slow_pickup", 0444, d_spin_debug,
&spinlock_stats.contention_stats[TAKEN_SLOW_PICKUP]);
debugfs_create_u32("released_slow", 0444, d_spin_debug,
&spinlock_stats.contention_stats[RELEASED_SLOW]);
debugfs_create_u32("released_slow_kicked", 0444, d_spin_debug,
&spinlock_stats.contention_stats[RELEASED_SLOW_KICKED]);
debugfs_create_u64("time_blocked", 0444, d_spin_debug,
&spinlock_stats.time_blocked);
debugfs_create_u32_array("histo_blocked", 0444, d_spin_debug,
spinlock_stats.histo_spin_blocked, HISTO_BUCKETS + 1);
return 0;
}
fs_initcall(kvm_spinlock_debugfs);
#else /* !CONFIG_KVM_DEBUG_FS */
static inline void add_stats(enum kvm_contention_stat var, u32 val)
{
}
static inline u64 spin_time_start(void)
{
return 0;
}
static inline void spin_time_accum_blocked(u64 start)
{
}
#endif /* CONFIG_KVM_DEBUG_FS */
struct kvm_lock_waiting {
struct arch_spinlock *lock;
__ticket_t want;
};
/* cpus 'waiting' on a spinlock to become available */
static cpumask_t waiting_cpus;
/* Track spinlock on which a cpu is waiting */
static DEFINE_PER_CPU(struct kvm_lock_waiting, klock_waiting);
__visible void kvm_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
{
struct kvm_lock_waiting *w;
int cpu;
u64 start;
unsigned long flags;
__ticket_t head;
if (in_nmi())
return;
w = this_cpu_ptr(&klock_waiting);
cpu = smp_processor_id();
start = spin_time_start();
/*
* Make sure an interrupt handler can't upset things in a
* partially setup state.
*/
local_irq_save(flags);
/*
* The ordering protocol on this is that the "lock" pointer
* may only be set non-NULL if the "want" ticket is correct.
* If we're updating "want", we must first clear "lock".
*/
w->lock = NULL;
smp_wmb();
w->want = want;
smp_wmb();
w->lock = lock;
add_stats(TAKEN_SLOW, 1);
/*
* This uses set_bit, which is atomic but we should not rely on its
* reordering gurantees. So barrier is needed after this call.
*/
cpumask_set_cpu(cpu, &waiting_cpus);
barrier();
/*
* Mark entry to slowpath before doing the pickup test to make
* sure we don't deadlock with an unlocker.
*/
__ticket_enter_slowpath(lock);
/* make sure enter_slowpath, which is atomic does not cross the read */
smp_mb__after_atomic();
/*
* check again make sure it didn't become free while
* we weren't looking.
*/
head = READ_ONCE(lock->tickets.head);
if (__tickets_equal(head, want)) {
add_stats(TAKEN_SLOW_PICKUP, 1);
goto out;
}
/*
* halt until it's our turn and kicked. Note that we do safe halt
* for irq enabled case to avoid hang when lock info is overwritten
* in irq spinlock slowpath and no spurious interrupt occur to save us.
*/
if (arch_irqs_disabled_flags(flags))
halt();
else
safe_halt();
out:
cpumask_clear_cpu(cpu, &waiting_cpus);
w->lock = NULL;
local_irq_restore(flags);
spin_time_accum_blocked(start);
}
PV_CALLEE_SAVE_REGS_THUNK(kvm_lock_spinning);
/* Kick vcpu waiting on @lock->head to reach value @ticket */
static void kvm_unlock_kick(struct arch_spinlock *lock, __ticket_t ticket)
{
int cpu;
add_stats(RELEASED_SLOW, 1);
for_each_cpu(cpu, &waiting_cpus) {
const struct kvm_lock_waiting *w = &per_cpu(klock_waiting, cpu);
if (READ_ONCE(w->lock) == lock &&
READ_ONCE(w->want) == ticket) {
add_stats(RELEASED_SLOW_KICKED, 1);
kvm_kick_cpu(cpu);
break;
}
}
}
#endif /* !CONFIG_QUEUED_SPINLOCKS */
/*
* Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present.
*/
@ -854,16 +614,11 @@ void __init kvm_spinlock_init(void)
if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT))
return;
#ifdef CONFIG_QUEUED_SPINLOCKS
__pv_init_lock_hash();
pv_lock_ops.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock);
pv_lock_ops.wait = kvm_wait;
pv_lock_ops.kick = kvm_kick_cpu;
#else /* !CONFIG_QUEUED_SPINLOCKS */
pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(kvm_lock_spinning);
pv_lock_ops.unlock_kick = kvm_unlock_kick;
#endif
}
static __init int kvm_spinlock_init_jump(void)

7
arch/x86/kernel/paravirt-spinlocks.c
View File

@ -8,7 +8,6 @@
#include <asm/paravirt.h>
#ifdef CONFIG_QUEUED_SPINLOCKS
__visible void __native_queued_spin_unlock(struct qspinlock *lock)
{
native_queued_spin_unlock(lock);
@ -21,19 +20,13 @@ bool pv_is_native_spin_unlock(void)
return pv_lock_ops.queued_spin_unlock.func ==
__raw_callee_save___native_queued_spin_unlock;
}
#endif
struct pv_lock_ops pv_lock_ops = {
#ifdef CONFIG_SMP
#ifdef CONFIG_QUEUED_SPINLOCKS
.queued_spin_lock_slowpath = native_queued_spin_lock_slowpath,
.queued_spin_unlock = PV_CALLEE_SAVE(__native_queued_spin_unlock),
.wait = paravirt_nop,
.kick = paravirt_nop,
#else /* !CONFIG_QUEUED_SPINLOCKS */
.lock_spinning = __PV_IS_CALLEE_SAVE(paravirt_nop),
.unlock_kick = paravirt_nop,
#endif /* !CONFIG_QUEUED_SPINLOCKS */
#endif /* SMP */
};
EXPORT_SYMBOL(pv_lock_ops);

4
arch/x86/kernel/paravirt_patch_32.c
View File

@ -10,7 +10,7 @@ DEF_NATIVE(pv_mmu_ops, write_cr3, "mov %eax, %cr3");
DEF_NATIVE(pv_mmu_ops, read_cr3, "mov %cr3, %eax");
DEF_NATIVE(pv_cpu_ops, clts, "clts");
#if defined(CONFIG_PARAVIRT_SPINLOCKS) && defined(CONFIG_QUEUED_SPINLOCKS)
#if defined(CONFIG_PARAVIRT_SPINLOCKS)
DEF_NATIVE(pv_lock_ops, queued_spin_unlock, "movb $0, (%eax)");
#endif
@ -49,7 +49,7 @@ unsigned native_patch(u8 type, u16 clobbers, void *ibuf,
PATCH_SITE(pv_mmu_ops, read_cr3);
PATCH_SITE(pv_mmu_ops, write_cr3);
PATCH_SITE(pv_cpu_ops, clts);
#if defined(CONFIG_PARAVIRT_SPINLOCKS) && defined(CONFIG_QUEUED_SPINLOCKS)
#if defined(CONFIG_PARAVIRT_SPINLOCKS)
case PARAVIRT_PATCH(pv_lock_ops.queued_spin_unlock):
if (pv_is_native_spin_unlock()) {
start = start_pv_lock_ops_queued_spin_unlock;

4
arch/x86/kernel/paravirt_patch_64.c
View File

@ -19,7 +19,7 @@ DEF_NATIVE(pv_cpu_ops, swapgs, "swapgs");
DEF_NATIVE(, mov32, "mov %edi, %eax");
DEF_NATIVE(, mov64, "mov %rdi, %rax");
#if defined(CONFIG_PARAVIRT_SPINLOCKS) && defined(CONFIG_QUEUED_SPINLOCKS)
#if defined(CONFIG_PARAVIRT_SPINLOCKS)
DEF_NATIVE(pv_lock_ops, queued_spin_unlock, "movb $0, (%rdi)");
#endif
@ -61,7 +61,7 @@ unsigned native_patch(u8 type, u16 clobbers, void *ibuf,
PATCH_SITE(pv_cpu_ops, clts);
PATCH_SITE(pv_mmu_ops, flush_tlb_single);
PATCH_SITE(pv_cpu_ops, wbinvd);
#if defined(CONFIG_PARAVIRT_SPINLOCKS) && defined(CONFIG_QUEUED_SPINLOCKS)
#if defined(CONFIG_PARAVIRT_SPINLOCKS)
case PARAVIRT_PATCH(pv_lock_ops.queued_spin_unlock):
if (pv_is_native_spin_unlock()) {
start = start_pv_lock_ops_queued_spin_unlock;

250
arch/x86/xen/spinlock.c
View File

@ -21,8 +21,6 @@ static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
static DEFINE_PER_CPU(char *, irq_name);
static bool xen_pvspin = true;
#ifdef CONFIG_QUEUED_SPINLOCKS
#include <asm/qspinlock.h>
static void xen_qlock_kick(int cpu)
@ -71,207 +69,6 @@ static void xen_qlock_wait(u8 *byte, u8 val)
xen_poll_irq(irq);
}
#else /* CONFIG_QUEUED_SPINLOCKS */
enum xen_contention_stat {
TAKEN_SLOW,
TAKEN_SLOW_PICKUP,
TAKEN_SLOW_SPURIOUS,
RELEASED_SLOW,
RELEASED_SLOW_KICKED,
NR_CONTENTION_STATS
};
#ifdef CONFIG_XEN_DEBUG_FS
#define HISTO_BUCKETS 30
static struct xen_spinlock_stats
{
u32 contention_stats[NR_CONTENTION_STATS];
u32 histo_spin_blocked[HISTO_BUCKETS+1];
u64 time_blocked;
} spinlock_stats;
static u8 zero_stats;
static inline void check_zero(void)
{
u8 ret;
u8 old = READ_ONCE(zero_stats);
if (unlikely(old)) {
ret = cmpxchg(&zero_stats, old, 0);
/* This ensures only one fellow resets the stat */
if (ret == old)
memset(&spinlock_stats, 0, sizeof(spinlock_stats));
}
}
static inline void add_stats(enum xen_contention_stat var, u32 val)
{
check_zero();
spinlock_stats.contention_stats[var] += val;
}
static inline u64 spin_time_start(void)
{
return xen_clocksource_read();
}
static void __spin_time_accum(u64 delta, u32 *array)
{
unsigned index = ilog2(delta);
check_zero();
if (index < HISTO_BUCKETS)
array[index]++;
else
array[HISTO_BUCKETS]++;
}
static inline void spin_time_accum_blocked(u64 start)
{
u32 delta = xen_clocksource_read() - start;
__spin_time_accum(delta, spinlock_stats.histo_spin_blocked);
spinlock_stats.time_blocked += delta;
}
#else /* !CONFIG_XEN_DEBUG_FS */
static inline void add_stats(enum xen_contention_stat var, u32 val)
{
}
static inline u64 spin_time_start(void)
{
return 0;
}
static inline void spin_time_accum_blocked(u64 start)
{
}
#endif /* CONFIG_XEN_DEBUG_FS */
struct xen_lock_waiting {
struct arch_spinlock *lock;
__ticket_t want;
};
static DEFINE_PER_CPU(struct xen_lock_waiting, lock_waiting);
static cpumask_t waiting_cpus;
__visible void xen_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
{
int irq = __this_cpu_read(lock_kicker_irq);
struct xen_lock_waiting *w = this_cpu_ptr(&lock_waiting);
int cpu = smp_processor_id();
u64 start;
__ticket_t head;
unsigned long flags;
/* If kicker interrupts not initialized yet, just spin */
if (irq == -1)
return;
start = spin_time_start();
/*
* Make sure an interrupt handler can't upset things in a
* partially setup state.
*/
local_irq_save(flags);
/*
* We don't really care if we're overwriting some other
* (lock,want) pair, as that would mean that we're currently
* in an interrupt context, and the outer context had
* interrupts enabled. That has already kicked the VCPU out
* of xen_poll_irq(), so it will just return spuriously and
* retry with newly setup (lock,want).
*
* The ordering protocol on this is that the "lock" pointer
* may only be set non-NULL if the "want" ticket is correct.
* If we're updating "want", we must first clear "lock".
*/
w->lock = NULL;
smp_wmb();
w->want = want;
smp_wmb();
w->lock = lock;
/* This uses set_bit, which atomic and therefore a barrier */
cpumask_set_cpu(cpu, &waiting_cpus);
add_stats(TAKEN_SLOW, 1);
/* clear pending */
xen_clear_irq_pending(irq);
/* Only check lock once pending cleared */
barrier();
/*
* Mark entry to slowpath before doing the pickup test to make
* sure we don't deadlock with an unlocker.
*/
__ticket_enter_slowpath(lock);
/* make sure enter_slowpath, which is atomic does not cross the read */
smp_mb__after_atomic();
/*
* check again make sure it didn't become free while
* we weren't looking
*/
head = READ_ONCE(lock->tickets.head);
if (__tickets_equal(head, want)) {
add_stats(TAKEN_SLOW_PICKUP, 1);
goto out;
}
/* Allow interrupts while blocked */
local_irq_restore(flags);
/*
* If an interrupt happens here, it will leave the wakeup irq
* pending, which will cause xen_poll_irq() to return
* immediately.
*/
/* Block until irq becomes pending (or perhaps a spurious wakeup) */
xen_poll_irq(irq);
add_stats(TAKEN_SLOW_SPURIOUS, !xen_test_irq_pending(irq));
local_irq_save(flags);
kstat_incr_irq_this_cpu(irq);
out:
cpumask_clear_cpu(cpu, &waiting_cpus);
w->lock = NULL;
local_irq_restore(flags);
spin_time_accum_blocked(start);
}
PV_CALLEE_SAVE_REGS_THUNK(xen_lock_spinning);
static void xen_unlock_kick(struct arch_spinlock *lock, __ticket_t next)
{
int cpu;
add_stats(RELEASED_SLOW, 1);
for_each_cpu(cpu, &waiting_cpus) {
const struct xen_lock_waiting *w = &per_cpu(lock_waiting, cpu);
/* Make sure we read lock before want */
if (READ_ONCE(w->lock) == lock &&
READ_ONCE(w->want) == next) {
add_stats(RELEASED_SLOW_KICKED, 1);
xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
break;
}
}
}
#endif /* CONFIG_QUEUED_SPINLOCKS */
static irqreturn_t dummy_handler(int irq, void *dev_id)
{
BUG();
@ -334,16 +131,12 @@ void __init xen_init_spinlocks(void)
return;
}
printk(KERN_DEBUG "xen: PV spinlocks enabled\n");
#ifdef CONFIG_QUEUED_SPINLOCKS
__pv_init_lock_hash();
pv_lock_ops.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock);
pv_lock_ops.wait = xen_qlock_wait;
pv_lock_ops.kick = xen_qlock_kick;
#else
pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(xen_lock_spinning);
pv_lock_ops.unlock_kick = xen_unlock_kick;
#endif
}
/*
@ -372,44 +165,3 @@ static __init int xen_parse_nopvspin(char *arg)
}
early_param("xen_nopvspin", xen_parse_nopvspin);
#if defined(CONFIG_XEN_DEBUG_FS) && !defined(CONFIG_QUEUED_SPINLOCKS)
static struct dentry *d_spin_debug;
static int __init xen_spinlock_debugfs(void)
{
struct dentry *d_xen = xen_init_debugfs();
if (d_xen == NULL)
return -ENOMEM;
if (!xen_pvspin)
return 0;
d_spin_debug = debugfs_create_dir("spinlocks", d_xen);
debugfs_create_u8("zero_stats", 0644, d_spin_debug, &zero_stats);
debugfs_create_u32("taken_slow", 0444, d_spin_debug,
&spinlock_stats.contention_stats[TAKEN_SLOW]);
debugfs_create_u32("taken_slow_pickup", 0444, d_spin_debug,
&spinlock_stats.contention_stats[TAKEN_SLOW_PICKUP]);
debugfs_create_u32("taken_slow_spurious", 0444, d_spin_debug,
&spinlock_stats.contention_stats[TAKEN_SLOW_SPURIOUS]);
debugfs_create_u32("released_slow", 0444, d_spin_debug,
&spinlock_stats.contention_stats[RELEASED_SLOW]);
debugfs_create_u32("released_slow_kicked", 0444, d_spin_debug,
&spinlock_stats.contention_stats[RELEASED_SLOW_KICKED]);
debugfs_create_u64("time_blocked", 0444, d_spin_debug,
&spinlock_stats.time_blocked);
debugfs_create_u32_array("histo_blocked", 0444, d_spin_debug,
spinlock_stats.histo_spin_blocked, HISTO_BUCKETS + 1);
return 0;
}
fs_initcall(xen_spinlock_debugfs);
#endif /* CONFIG_XEN_DEBUG_FS */