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powerpc/qspinlock: don't propagate the not-sleepy state

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To simplify things, don't propagate the not-sleepy condition back down
the queue. Instead, have the waiters clear their own node->sleepy when
finding the lock owner is not preempted.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Tested-by: Shrikanth Hegde <sshegde@linux.vnet.ibm.com>
Reviewed-by: "Nysal Jan K.A" <nysal@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20231016124305.139923-5-npiggin@gmail.com
This commit is contained in:
Nicholas Piggin 2023-10-16 22:43:03 +10:00 committed by Michael Ellerman
parent fd8fae50c9
commit fcf77d4427
1 changed files with 8 additions and 18 deletions
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26
arch/powerpc/lib/qspinlock.c
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@ -350,7 +350,7 @@ static __always_inline bool yield_head_to_locked_owner(struct qspinlock *lock, u
return __yield_to_locked_owner(lock, val, paravirt, mustq);
}
static __always_inline void propagate_sleepy(struct qnode *node, u32 val, bool *set_sleepy, bool paravirt)
static __always_inline void propagate_sleepy(struct qnode *node, u32 val, bool paravirt)
{
struct qnode *next;
int owner;
@ -359,18 +359,17 @@ static __always_inline void propagate_sleepy(struct qnode *node, u32 val, bool *
return;
if (!pv_yield_propagate_owner)
return;
if (*set_sleepy)
return;
next = READ_ONCE(node->next);
if (!next)
return;
if (next->sleepy)
return;
owner = get_owner_cpu(val);
if (vcpu_is_preempted(owner)) {
if (vcpu_is_preempted(owner))
next->sleepy = 1;
*set_sleepy = true;
}
}
/* Called inside spin_begin() */
@ -385,12 +384,7 @@ static __always_inline bool yield_to_prev(struct qspinlock *lock, struct qnode *
if (!pv_yield_propagate_owner)
goto yield_prev;
if (!READ_ONCE(node->sleepy)) {
/* Propagate back sleepy==false */
if (node->next && node->next->sleepy)
node->next->sleepy = 0;
goto yield_prev;
} else {
if (node->sleepy) {
u32 val = READ_ONCE(lock->val);
if (val & _Q_LOCKED_VAL) {
@ -410,6 +404,7 @@ static __always_inline bool yield_to_prev(struct qspinlock *lock, struct qnode *
if (preempted)
return preempted;
}
node->sleepy = false;
}
yield_prev:
@ -533,7 +528,6 @@ static __always_inline void queued_spin_lock_mcs_queue(struct qspinlock *lock, b
bool sleepy = false;
bool mustq = false;
int idx;
bool set_sleepy = false;
int iters = 0;
BUILD_BUG_ON(CONFIG_NR_CPUS >= (1U << _Q_TAIL_CPU_BITS));
@ -591,10 +585,6 @@ static __always_inline void queued_spin_lock_mcs_queue(struct qspinlock *lock, b
spec_barrier();
spin_end();
/* Clear out stale propagated sleepy */
if (paravirt && pv_yield_propagate_owner && node->sleepy)
node->sleepy = 0;
smp_rmb(); /* acquire barrier for the mcs lock */
/*
@ -636,7 +626,7 @@ again:
}
}
propagate_sleepy(node, val, &set_sleepy, paravirt);
propagate_sleepy(node, val, paravirt);
preempted = yield_head_to_locked_owner(lock, val, paravirt);
if (!maybe_stealers)
continue;