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Diffstat (limited to 'arch/powerpc/include/asm/qspinlock.h')
-rw-r--r--arch/powerpc/include/asm/qspinlock.h192
1 files changed, 141 insertions, 51 deletions
diff --git a/arch/powerpc/include/asm/qspinlock.h b/arch/powerpc/include/asm/qspinlock.h
index b676c4fb90fd..28a53fb69b38 100644
--- a/arch/powerpc/include/asm/qspinlock.h
+++ b/arch/powerpc/include/asm/qspinlock.h
@@ -2,83 +2,173 @@
#ifndef _ASM_POWERPC_QSPINLOCK_H
#define _ASM_POWERPC_QSPINLOCK_H
-#include <asm-generic/qspinlock_types.h>
+#include <linux/compiler.h>
+#include <asm/qspinlock_types.h>
#include <asm/paravirt.h>
-#define _Q_PENDING_LOOPS (1 << 9) /* not tuned */
+#ifdef CONFIG_PPC64
+/*
+ * Use the EH=1 hint for accesses that result in the lock being acquired.
+ * The hardware is supposed to optimise this pattern by holding the lock
+ * cacheline longer, and releasing when a store to the same memory (the
+ * unlock) is performed.
+ */
+#define _Q_SPIN_EH_HINT 1
+#else
+#define _Q_SPIN_EH_HINT 0
+#endif
-#ifdef CONFIG_PARAVIRT_SPINLOCKS
-extern void native_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
-extern void __pv_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
-extern void __pv_queued_spin_unlock(struct qspinlock *lock);
+/*
+ * The trylock itself may steal. This makes trylocks slightly stronger, and
+ * makes locks slightly more efficient when stealing.
+ *
+ * This is compile-time, so if true then there may always be stealers, so the
+ * nosteal paths become unused.
+ */
+#define _Q_SPIN_TRY_LOCK_STEAL 1
-static __always_inline void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
-{
- if (!is_shared_processor())
- native_queued_spin_lock_slowpath(lock, val);
- else
- __pv_queued_spin_lock_slowpath(lock, val);
-}
+/*
+ * Put a speculation barrier after testing the lock/node and finding it
+ * busy. Try to prevent pointless speculation in slow paths.
+ *
+ * Slows down the lockstorm microbenchmark with no stealing, where locking
+ * is purely FIFO through the queue. May have more benefit in real workload
+ * where speculating into the wrong place could have a greater cost.
+ */
+#define _Q_SPIN_SPEC_BARRIER 0
-#define queued_spin_unlock queued_spin_unlock
-static inline void queued_spin_unlock(struct qspinlock *lock)
-{
- if (!is_shared_processor())
- smp_store_release(&lock->locked, 0);
- else
- __pv_queued_spin_unlock(lock);
-}
+#ifdef CONFIG_PPC64
+/*
+ * Execute a miso instruction after passing the MCS lock ownership to the
+ * queue head. Miso is intended to make stores visible to other CPUs sooner.
+ *
+ * This seems to make the lockstorm microbenchmark nospin test go slightly
+ * faster on POWER10, but disable for now.
+ */
+#define _Q_SPIN_MISO 0
+#else
+#define _Q_SPIN_MISO 0
+#endif
+#ifdef CONFIG_PPC64
+/*
+ * This executes miso after an unlock of the lock word, having ownership
+ * pass to the next CPU sooner. This will slow the uncontended path to some
+ * degree. Not evidence it helps yet.
+ */
+#define _Q_SPIN_MISO_UNLOCK 0
#else
-extern void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
+#define _Q_SPIN_MISO_UNLOCK 0
#endif
-static __always_inline void queued_spin_lock(struct qspinlock *lock)
+/*
+ * Seems to slow down lockstorm microbenchmark, suspect queue node just
+ * has to become shared again right afterwards when its waiter spins on
+ * the lock field.
+ */
+#define _Q_SPIN_PREFETCH_NEXT 0
+
+static __always_inline int queued_spin_is_locked(struct qspinlock *lock)
{
- u32 val = 0;
+ return READ_ONCE(lock->val);
+}
- if (likely(arch_atomic_try_cmpxchg_lock(&lock->val, &val, _Q_LOCKED_VAL)))
- return;
+static __always_inline int queued_spin_value_unlocked(struct qspinlock lock)
+{
+ return !lock.val;
+}
- queued_spin_lock_slowpath(lock, val);
+static __always_inline int queued_spin_is_contended(struct qspinlock *lock)
+{
+ return !!(READ_ONCE(lock->val) & _Q_TAIL_CPU_MASK);
}
-#define queued_spin_lock queued_spin_lock
-#ifdef CONFIG_PARAVIRT_SPINLOCKS
-#define SPIN_THRESHOLD (1<<15) /* not tuned */
+static __always_inline u32 queued_spin_encode_locked_val(void)
+{
+ /* XXX: make this use lock value in paca like simple spinlocks? */
+ return _Q_LOCKED_VAL | (smp_processor_id() << _Q_OWNER_CPU_OFFSET);
+}
-static __always_inline void pv_wait(u8 *ptr, u8 val)
+static __always_inline int __queued_spin_trylock_nosteal(struct qspinlock *lock)
{
- if (*ptr != val)
- return;
- yield_to_any();
- /*
- * We could pass in a CPU here if waiting in the queue and yield to
- * the previous CPU in the queue.
- */
+ u32 new = queued_spin_encode_locked_val();
+ u32 prev;
+
+ /* Trylock succeeds only when unlocked and no queued nodes */
+ asm volatile(
+"1: lwarx %0,0,%1,%3 # __queued_spin_trylock_nosteal \n"
+" cmpwi 0,%0,0 \n"
+" bne- 2f \n"
+" stwcx. %2,0,%1 \n"
+" bne- 1b \n"
+"\t" PPC_ACQUIRE_BARRIER " \n"
+"2: \n"
+ : "=&r" (prev)
+ : "r" (&lock->val), "r" (new),
+ "i" (_Q_SPIN_EH_HINT)
+ : "cr0", "memory");
+
+ return likely(prev == 0);
}
-static __always_inline void pv_kick(int cpu)
+static __always_inline int __queued_spin_trylock_steal(struct qspinlock *lock)
{
- prod_cpu(cpu);
+ u32 new = queued_spin_encode_locked_val();
+ u32 prev, tmp;
+
+ /* Trylock may get ahead of queued nodes if it finds unlocked */
+ asm volatile(
+"1: lwarx %0,0,%2,%5 # __queued_spin_trylock_steal \n"
+" andc. %1,%0,%4 \n"
+" bne- 2f \n"
+" and %1,%0,%4 \n"
+" or %1,%1,%3 \n"
+" stwcx. %1,0,%2 \n"
+" bne- 1b \n"
+"\t" PPC_ACQUIRE_BARRIER " \n"
+"2: \n"
+ : "=&r" (prev), "=&r" (tmp)
+ : "r" (&lock->val), "r" (new), "r" (_Q_TAIL_CPU_MASK),
+ "i" (_Q_SPIN_EH_HINT)
+ : "cr0", "memory");
+
+ return likely(!(prev & ~_Q_TAIL_CPU_MASK));
}
-extern void __pv_init_lock_hash(void);
+static __always_inline int queued_spin_trylock(struct qspinlock *lock)
+{
+ if (!_Q_SPIN_TRY_LOCK_STEAL)
+ return __queued_spin_trylock_nosteal(lock);
+ else
+ return __queued_spin_trylock_steal(lock);
+}
-static inline void pv_spinlocks_init(void)
+void queued_spin_lock_slowpath(struct qspinlock *lock);
+
+static __always_inline void queued_spin_lock(struct qspinlock *lock)
{
- __pv_init_lock_hash();
+ if (!queued_spin_trylock(lock))
+ queued_spin_lock_slowpath(lock);
}
-#endif
+static inline void queued_spin_unlock(struct qspinlock *lock)
+{
+ smp_store_release(&lock->locked, 0);
+ if (_Q_SPIN_MISO_UNLOCK)
+ asm volatile("miso" ::: "memory");
+}
-/*
- * Queued spinlocks rely heavily on smp_cond_load_relaxed() to busy-wait,
- * which was found to have performance problems if implemented with
- * the preferred spin_begin()/spin_end() SMT priority pattern. Use the
- * generic version instead.
- */
+#define arch_spin_is_locked(l) queued_spin_is_locked(l)
+#define arch_spin_is_contended(l) queued_spin_is_contended(l)
+#define arch_spin_value_unlocked(l) queued_spin_value_unlocked(l)
+#define arch_spin_lock(l) queued_spin_lock(l)
+#define arch_spin_trylock(l) queued_spin_trylock(l)
+#define arch_spin_unlock(l) queued_spin_unlock(l)
-#include <asm-generic/qspinlock.h>
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+void pv_spinlocks_init(void);
+#else
+static inline void pv_spinlocks_init(void) { }
+#endif
#endif /* _ASM_POWERPC_QSPINLOCK_H */