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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-changelog] [xen master] Revert "use ticket locks for spin locks"
commit 818e376d3b17845d39735517650224c64c9e0078
Author: Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Thu May 28 12:07:33 2015 +0200
Commit: Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu May 28 12:07:33 2015 +0200
Revert "use ticket locks for spin locks"
This reverts commit 45fcc4568c5162b00fb3907fb158af82dd484a3d as it
introduces yet to be explained issues on ARM.
---
xen/common/spinlock.c | 116 ++++++++++++++++++------------------------
xen/include/asm-arm/system.h | 3 -
xen/include/asm-x86/system.h | 11 ----
xen/include/xen/spinlock.h | 16 ++----
4 files changed, 54 insertions(+), 92 deletions(-)
diff --git a/xen/common/spinlock.c b/xen/common/spinlock.c
index c8dc8ba..5fd8b1c 100644
--- a/xen/common/spinlock.c
+++ b/xen/common/spinlock.c
@@ -115,134 +115,125 @@ void spin_debug_disable(void)
#endif
-static always_inline spinlock_tickets_t observe_lock(spinlock_tickets_t *t)
-{
- spinlock_tickets_t v;
-
- smp_rmb();
- v.head_tail = read_atomic(&t->head_tail);
- return v;
-}
-
-static always_inline u16 observe_head(spinlock_tickets_t *t)
-{
- smp_rmb();
- return read_atomic(&t->head);
-}
-
void _spin_lock(spinlock_t *lock)
{
- spinlock_tickets_t tickets = { .tail = 1, };
LOCK_PROFILE_VAR;
check_lock(&lock->debug);
- tickets.head_tail = arch_fetch_and_add(&lock->tickets.head_tail,
- tickets.head_tail);
- while ( tickets.tail != observe_head(&lock->tickets) )
+ while ( unlikely(!_raw_spin_trylock(&lock->raw)) )
{
LOCK_PROFILE_BLOCK;
- cpu_relax();
+ while ( likely(_raw_spin_is_locked(&lock->raw)) )
+ cpu_relax();
}
LOCK_PROFILE_GOT;
preempt_disable();
- arch_lock_acquire_barrier();
}
void _spin_lock_irq(spinlock_t *lock)
{
+ LOCK_PROFILE_VAR;
+
ASSERT(local_irq_is_enabled());
local_irq_disable();
- _spin_lock(lock);
+ check_lock(&lock->debug);
+ while ( unlikely(!_raw_spin_trylock(&lock->raw)) )
+ {
+ LOCK_PROFILE_BLOCK;
+ local_irq_enable();
+ while ( likely(_raw_spin_is_locked(&lock->raw)) )
+ cpu_relax();
+ local_irq_disable();
+ }
+ LOCK_PROFILE_GOT;
+ preempt_disable();
}
unsigned long _spin_lock_irqsave(spinlock_t *lock)
{
unsigned long flags;
+ LOCK_PROFILE_VAR;
local_irq_save(flags);
- _spin_lock(lock);
+ check_lock(&lock->debug);
+ while ( unlikely(!_raw_spin_trylock(&lock->raw)) )
+ {
+ LOCK_PROFILE_BLOCK;
+ local_irq_restore(flags);
+ while ( likely(_raw_spin_is_locked(&lock->raw)) )
+ cpu_relax();
+ local_irq_disable();
+ }
+ LOCK_PROFILE_GOT;
+ preempt_disable();
return flags;
}
void _spin_unlock(spinlock_t *lock)
{
- arch_lock_release_barrier();
preempt_enable();
LOCK_PROFILE_REL;
- add_sized(&lock->tickets.head, 1);
+ _raw_spin_unlock(&lock->raw);
}
void _spin_unlock_irq(spinlock_t *lock)
{
- _spin_unlock(lock);
+ preempt_enable();
+ LOCK_PROFILE_REL;
+ _raw_spin_unlock(&lock->raw);
local_irq_enable();
}
void _spin_unlock_irqrestore(spinlock_t *lock, unsigned long flags)
{
- _spin_unlock(lock);
+ preempt_enable();
+ LOCK_PROFILE_REL;
+ _raw_spin_unlock(&lock->raw);
local_irq_restore(flags);
}
int _spin_is_locked(spinlock_t *lock)
{
check_lock(&lock->debug);
- return lock->tickets.head != lock->tickets.tail;
+ return _raw_spin_is_locked(&lock->raw);
}
int _spin_trylock(spinlock_t *lock)
{
- spinlock_tickets_t old, new;
-
check_lock(&lock->debug);
- old = observe_lock(&lock->tickets);
- if ( old.head != old.tail )
- return 0;
- new = old;
- new.tail++;
- if ( cmpxchg(&lock->tickets.head_tail,
- old.head_tail, new.head_tail) != old.head_tail )
+ if ( !_raw_spin_trylock(&lock->raw) )
return 0;
#ifdef LOCK_PROFILE
if (lock->profile)
lock->profile->time_locked = NOW();
#endif
preempt_disable();
- /*
- * cmpxchg() is a full barrier so no need for an
- * arch_lock_acquire_barrier().
- */
return 1;
}
void _spin_barrier(spinlock_t *lock)
{
- spinlock_tickets_t sample;
#ifdef LOCK_PROFILE
s_time_t block = NOW();
-#endif
+ u64 loop = 0;
check_barrier(&lock->debug);
- smp_mb();
- sample = observe_lock(&lock->tickets);
- if ( sample.head != sample.tail )
+ do { smp_mb(); loop++;} while ( _raw_spin_is_locked(&lock->raw) );
+ if ((loop > 1) && lock->profile)
{
- while ( observe_head(&lock->tickets) == sample.head )
- cpu_relax();
-#ifdef LOCK_PROFILE
- if ( lock->profile )
- {
- lock->profile->time_block += NOW() - block;
- lock->profile->block_cnt++;
- }
-#endif
+ lock->profile->time_block += NOW() - block;
+ lock->profile->block_cnt++;
}
+#else
+ check_barrier(&lock->debug);
+ do { smp_mb(); } while ( _raw_spin_is_locked(&lock->raw) );
+#endif
smp_mb();
}
int _spin_trylock_recursive(spinlock_t *lock)
{
- unsigned int cpu = smp_processor_id();
+ int cpu = smp_processor_id();
/* Don't allow overflow of recurse_cpu field. */
BUILD_BUG_ON(NR_CPUS > 0xfffu);
@@ -265,17 +256,8 @@ int _spin_trylock_recursive(spinlock_t *lock)
void _spin_lock_recursive(spinlock_t *lock)
{
- unsigned int cpu = smp_processor_id();
-
- if ( likely(lock->recurse_cpu != cpu) )
- {
- _spin_lock(lock);
- lock->recurse_cpu = cpu;
- }
-
- /* We support only fairly shallow recursion, else the counter overflows. */
- ASSERT(lock->recurse_cnt < 0xfu);
- lock->recurse_cnt++;
+ while ( !spin_trylock_recursive(lock) )
+ cpu_relax();
}
void _spin_unlock_recursive(spinlock_t *lock)
diff --git a/xen/include/asm-arm/system.h b/xen/include/asm-arm/system.h
index f0e222f..2eb96e8 100644
--- a/xen/include/asm-arm/system.h
+++ b/xen/include/asm-arm/system.h
@@ -53,9 +53,6 @@
#define arch_fetch_and_add(x, v) __sync_fetch_and_add(x, v)
-#define arch_lock_acquire_barrier() smp_mb()
-#define arch_lock_release_barrier() smp_mb()
-
extern struct vcpu *__context_switch(struct vcpu *prev, struct vcpu *next);
#endif
diff --git a/xen/include/asm-x86/system.h b/xen/include/asm-x86/system.h
index 25a6a2a..9fb70f5 100644
--- a/xen/include/asm-x86/system.h
+++ b/xen/include/asm-x86/system.h
@@ -185,17 +185,6 @@ static always_inline unsigned long __xadd(
#define set_mb(var, value) do { xchg(&var, value); } while (0)
#define set_wmb(var, value) do { var = value; wmb(); } while (0)
-/*
- * On x86 the only reordering is of reads with older writes. In the
- * lock case, the read in observe_head() can only be reordered with
- * writes that precede it, and moving a write _into_ a locked section
- * is OK. In the release case, the write in add_sized() can only be
- * reordered with reads that follow it, and hoisting a read _into_ a
- * locked region is OK.
- */
-#define arch_lock_acquire_barrier() barrier()
-#define arch_lock_release_barrier() barrier()
-
#define local_irq_disable() asm volatile ( "cli" : : : "memory" )
#define local_irq_enable() asm volatile ( "sti" : : : "memory" )
diff --git a/xen/include/xen/spinlock.h b/xen/include/xen/spinlock.h
index bafbc74..eda9b2e 100644
--- a/xen/include/xen/spinlock.h
+++ b/xen/include/xen/spinlock.h
@@ -80,7 +80,8 @@ struct lock_profile_qhead {
static struct lock_profile *__lock_profile_##name \
__used_section(".lockprofile.data") = \
&__lock_profile_data_##name
-#define _SPIN_LOCK_UNLOCKED(x) { { 0 }, 0xfffu, 0, _LOCK_DEBUG, x }
+#define _SPIN_LOCK_UNLOCKED(x) { _RAW_SPIN_LOCK_UNLOCKED, 0xfffu, 0, \
+ _LOCK_DEBUG, x }
#define SPIN_LOCK_UNLOCKED _SPIN_LOCK_UNLOCKED(NULL)
#define DEFINE_SPINLOCK(l) \
spinlock_t l = _SPIN_LOCK_UNLOCKED(NULL); \
@@ -116,7 +117,8 @@ extern void spinlock_profile_reset(unsigned char key);
struct lock_profile_qhead { };
-#define SPIN_LOCK_UNLOCKED { { 0 }, 0xfffu, 0, _LOCK_DEBUG }
+#define SPIN_LOCK_UNLOCKED \
+ { _RAW_SPIN_LOCK_UNLOCKED, 0xfffu, 0, _LOCK_DEBUG }
#define DEFINE_SPINLOCK(l) spinlock_t l = SPIN_LOCK_UNLOCKED
#define spin_lock_init_prof(s, l) spin_lock_init(&((s)->l))
@@ -125,16 +127,8 @@ struct lock_profile_qhead { };
#endif
-typedef union {
- u32 head_tail;
- struct {
- u16 head;
- u16 tail;
- };
-} spinlock_tickets_t;
-
typedef struct spinlock {
- spinlock_tickets_t tickets;
+ raw_spinlock_t raw;
u16 recurse_cpu:12;
u16 recurse_cnt:4;
struct lock_debug debug;
--
generated by git-patchbot for /home/xen/git/xen.git#master
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