Use the spin_begin/spin_cpu_relax/spin_end APIs in qspinlock, which helps
to prevent threads issuing a lot of expensive priority nops which may not
have much effect due to immediately executing low then medium priority.
Signed-off-by: Nicholas Piggin <npig...@gmail.com>
---
arch/powerpc/lib/qspinlock.c | 39 ++++++++++++++++++++++++++++++++----
1 file changed, 35 insertions(+), 4 deletions(-)
diff --git a/arch/powerpc/lib/qspinlock.c b/arch/powerpc/lib/qspinlock.c
index 1cb47a6478a0..70f924296b36 100644
--- a/arch/powerpc/lib/qspinlock.c
+++ b/arch/powerpc/lib/qspinlock.c
@@ -184,6 +184,7 @@ static struct qnode *get_tail_qnode(struct qspinlock *lock,
u32 val)
BUG();
}
+/* Called inside spin_begin() */
static __always_inline void __yield_to_locked_owner(struct qspinlock *lock,
u32 val, bool paravirt, bool mustq)
{
int owner;
@@ -203,6 +204,8 @@ static __always_inline void __yield_to_locked_owner(struct
qspinlock *lock, u32
if ((yield_count & 1) == 0)
goto relax; /* owner vcpu is running */
+ spin_end();
+
/*
* Read the lock word after sampling the yield count. On the other side
* there may a wmb because the yield count update is done by the
@@ -218,18 +221,22 @@ static __always_inline void
__yield_to_locked_owner(struct qspinlock *lock, u32
yield_to_preempted(owner, yield_count);
if (mustq)
set_mustq(lock);
+ spin_begin();
/* Don't relax if we yielded. Maybe we should? */
return;
}
+ spin_begin();
relax:
- cpu_relax();
+ spin_cpu_relax();
}
+/* Called inside spin_begin() */
static __always_inline void yield_to_locked_owner(struct qspinlock *lock, u32
val, bool paravirt)
{
__yield_to_locked_owner(lock, val, paravirt, false);
}
+/* Called inside spin_begin() */
static __always_inline void yield_head_to_locked_owner(struct qspinlock *lock,
u32 val, bool paravirt)
{
bool mustq = false;
@@ -267,6 +274,7 @@ static __always_inline void propagate_yield_cpu(struct
qnode *node, u32 val, int
}
}
+/* Called inside spin_begin() */
static __always_inline void yield_to_prev(struct qspinlock *lock, struct qnode
*node, u32 val, bool paravirt)
{
int prev_cpu = decode_tail_cpu(val);
@@ -291,14 +299,18 @@ static __always_inline void yield_to_prev(struct
qspinlock *lock, struct qnode *
if ((yield_count & 1) == 0)
goto yield_prev; /* owner vcpu is running */
+ spin_end();
+
smp_rmb();
if (yield_cpu == node->yield_cpu) {
if (node->next && node->next->yield_cpu != yield_cpu)
node->next->yield_cpu = yield_cpu;
yield_to_preempted(yield_cpu, yield_count);
+ spin_begin();
return;
}
+ spin_begin();
yield_prev:
if (!pv_yield_prev)
@@ -308,15 +320,19 @@ static __always_inline void yield_to_prev(struct
qspinlock *lock, struct qnode *
if ((yield_count & 1) == 0)
goto relax; /* owner vcpu is running */
+ spin_end();
+
smp_rmb(); /* See __yield_to_locked_owner comment */
if (!node->locked) {
yield_to_preempted(prev_cpu, yield_count);
+ spin_begin();
return;
}
+ spin_begin();
relax:
- cpu_relax();
+ spin_cpu_relax();
}
@@ -328,6 +344,8 @@ static __always_inline bool try_to_steal_lock(struct
qspinlock *lock, bool parav
return false;
/* Attempt to steal the lock */
+ spin_begin();
+
do {
u32 val = READ_ONCE(lock->val);
@@ -335,8 +353,10 @@ static __always_inline bool try_to_steal_lock(struct
qspinlock *lock, bool parav
break;
if (unlikely(!(val & _Q_LOCKED_VAL))) {
+ spin_end();
if (__queued_spin_trylock_steal(lock))
return true;
+ spin_begin();
} else {
yield_to_locked_owner(lock, val, paravirt);
}
@@ -344,6 +364,8 @@ static __always_inline bool try_to_steal_lock(struct
qspinlock *lock, bool parav
iters++;
} while (iters < get_steal_spins(paravirt));
+ spin_end();
+
return false;
}
@@ -395,8 +417,10 @@ static __always_inline void
queued_spin_lock_mcs_queue(struct qspinlock *lock, b
WRITE_ONCE(prev->next, node);
/* Wait for mcs node lock to be released */
+ spin_begin();
while (!node->locked)
yield_to_prev(lock, node, old, paravirt);
+ spin_end();
/* Clear out stale propagated yield_cpu */
if (paravirt && pv_yield_propagate_owner && node->yield_cpu !=
-1)
@@ -407,6 +431,7 @@ static __always_inline void
queued_spin_lock_mcs_queue(struct qspinlock *lock, b
again:
/* We're at the head of the waitqueue, wait for the lock. */
+ spin_begin();
for (;;) {
val = READ_ONCE(lock->val);
if (!(val & _Q_LOCKED_VAL))
@@ -424,6 +449,7 @@ static __always_inline void
queued_spin_lock_mcs_queue(struct qspinlock *lock, b
val |= _Q_MUST_Q_VAL;
}
}
+ spin_end();
/* If we're the last queued, must clean up the tail. */
old = trylock_clean_tail(lock, tail);
@@ -436,8 +462,13 @@ static __always_inline void
queued_spin_lock_mcs_queue(struct qspinlock *lock, b
goto release; /* We were the tail, no next. */
/* There is a next, must wait for node->next != NULL (MCS protocol) */
- while (!(next = READ_ONCE(node->next)))
- cpu_relax();
+ next = READ_ONCE(node->next);
+ if (!next) {
+ spin_begin();
+ while (!(next = READ_ONCE(node->next)))
+ cpu_relax();
+ spin_end();
+ }
/*
* Unlock the next mcs waiter node. Release barrier is not required
--
2.37.2
