[PATCH v7 2/5] locking/qspinlock: Refactor the qspinlock slow path

Alex Kogan
2019-11-25T21:16:30Z

Move some of the code manipulating the spin lock into separate functions.
This would allow easier integration of alternative ways to manipulate
that lock.

Signed-off-by: Alex Kogan <alex.kogan@oracle.com>
Reviewed-by: Steve Sistare <steven.sistare@oracle.com>
---
kernel/locking/qspinlock.c | 38 ++++++++++++++++++++++++++++++++++++--
1 file changed, 36 insertions(+), 2 deletions(-)

diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index 804c0fbd6328..c06d1e8075d9 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -288,6 +288,34 @@ static __always_inline u32 __pv_wait_head_or_lock(struct qspinlock *lock,
#define queued_spin_lock_slowpath native_queued_spin_lock_slowpath
#endif

+/*
+ * __try_clear_tail - try to clear tail by setting the lock value to
+ * _Q_LOCKED_VAL.
+ * @lock: Pointer to the queued spinlock structure
+ * @val: Current value of the lock
+ * @node: Pointer to the MCS node of the lock holder
+ */
+static __always_inline bool __try_clear_tail(struct qspinlock *lock,
+ u32 val,
+ struct mcs_spinlock *node)
+{
+ return atomic_try_cmpxchg_relaxed(&lock->val, &val, _Q_LOCKED_VAL);
+}
+
+/*
+ * __mcs_pass_lock - pass the MCS lock to the next waiter
+ * @node: Pointer to the MCS node of the lock holder
+ * @next: Pointer to the MCS node of the first waiter in the MCS queue
+ */
+static __always_inline void __mcs_pass_lock(struct mcs_spinlock *node,
+ struct mcs_spinlock *next)
+{
+ arch_mcs_pass_lock(&next->locked, 1);
+}
+
+#define try_clear_tail __try_clear_tail
+#define mcs_pass_lock __mcs_pass_lock
+
#endif /* _GEN_PV_LOCK_SLOWPATH */

/**
@@ -532,7 +560,7 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
* PENDING will make the uncontended transition fail.
*/
if ((val & _Q_TAIL_MASK) == tail) {
- if (atomic_try_cmpxchg_relaxed(&lock->val, &val, _Q_LOCKED_VAL))
+ if (try_clear_tail(lock, val, node))
goto release; /* No contention */
}

@@ -549,7 +577,7 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
if (!next)
next = smp_cond_load_relaxed(&node->next, (VAL));

- arch_mcs_pass_lock(&next->locked, 1);
+ mcs_pass_lock(node, next);
pv_kick_node(lock, next);

release:
@@ -574,6 +602,12 @@ EXPORT_SYMBOL(queued_spin_lock_slowpath);
#undef pv_kick_node
#undef pv_wait_head_or_lock

+#undef try_clear_tail
+#define try_clear_tail __try_clear_tail
+
+#undef mcs_pass_lock
+#define mcs_pass_lock __mcs_pass_lock
+
#undef queued_spin_lock_slowpath
#define queued_spin_lock_slowpath __pv_queued_spin_lock_slowpath

--
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