[PATCH v5 1/7] locking/qspinlock: Add ARCH_USE_QUEUED_SPINLOCKS_XCHG32
From: guoren@kernel.org
Date: 2021-03-28 06:32:27
Also in:
linux-arch, linux-riscv, lkml, sparclinux
Subsystem:
locking primitives, the rest · Maintainers:
Peter Zijlstra, Ingo Molnar, Will Deacon, Boqun Feng, Linus Torvalds
From: Guo Ren <redacted> Some architectures don't have sub-word swap atomic instruction, they only have the full word's one. The sub-word swap only improve the performance when: NR_CPUS < 16K * 0- 7: locked byte * 8: pending * 9-15: not used * 16-17: tail index * 18-31: tail cpu (+1) The 9-15 bits are wasted to use xchg16 in xchg_tail. Please let architecture select xchg16/xchg32 to implement xchg_tail. Signed-off-by: Guo Ren <redacted> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Will Deacon <will@kernel.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Waiman Long <longman@redhat.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Anup Patel <anup@brainfault.org> --- kernel/Kconfig.locks | 3 +++ kernel/locking/qspinlock.c | 46 +++++++++++++++++++++----------------- 2 files changed, 28 insertions(+), 21 deletions(-)
diff --git a/kernel/Kconfig.locks b/kernel/Kconfig.locks
index 3de8fd11873b..d02f1261f73f 100644
--- a/kernel/Kconfig.locks
+++ b/kernel/Kconfig.locks@@ -239,6 +239,9 @@ config LOCK_SPIN_ON_OWNER config ARCH_USE_QUEUED_SPINLOCKS bool +config ARCH_USE_QUEUED_SPINLOCKS_XCHG32 + bool + config QUEUED_SPINLOCKS def_bool y if ARCH_USE_QUEUED_SPINLOCKS depends on SMP
diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index cbff6ba53d56..4bfaa969bd15 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c@@ -163,26 +163,6 @@ static __always_inline void clear_pending_set_locked(struct qspinlock *lock) WRITE_ONCE(lock->locked_pending, _Q_LOCKED_VAL); } -/* - * xchg_tail - Put in the new queue tail code word & retrieve previous one - * @lock : Pointer to queued spinlock structure - * @tail : The new queue tail code word - * Return: The previous queue tail code word - * - * xchg(lock, tail), which heads an address dependency - * - * p,*,* -> n,*,* ; prev = xchg(lock, node) - */ -static __always_inline u32 xchg_tail(struct qspinlock *lock, u32 tail) -{ - /* - * We can use relaxed semantics since the caller ensures that the - * MCS node is properly initialized before updating the tail. - */ - return (u32)xchg_relaxed(&lock->tail, - tail >> _Q_TAIL_OFFSET) << _Q_TAIL_OFFSET; -} - #else /* _Q_PENDING_BITS == 8 */ /**
@@ -206,6 +186,30 @@ static __always_inline void clear_pending_set_locked(struct qspinlock *lock) { atomic_add(-_Q_PENDING_VAL + _Q_LOCKED_VAL, &lock->val); } +#endif /* _Q_PENDING_BITS == 8 */ + +#if _Q_PENDING_BITS == 8 && !defined(CONFIG_ARCH_USE_QUEUED_SPINLOCKS_XCHG32) +/* + * xchg_tail - Put in the new queue tail code word & retrieve previous one + * @lock : Pointer to queued spinlock structure + * @tail : The new queue tail code word + * Return: The previous queue tail code word + * + * xchg(lock, tail), which heads an address dependency + * + * p,*,* -> n,*,* ; prev = xchg(lock, node) + */ +static __always_inline u32 xchg_tail(struct qspinlock *lock, u32 tail) +{ + /* + * We can use relaxed semantics since the caller ensures that the + * MCS node is properly initialized before updating the tail. + */ + return (u32)xchg_relaxed(&lock->tail, + tail >> _Q_TAIL_OFFSET) << _Q_TAIL_OFFSET; +} + +#else /** * xchg_tail - Put in the new queue tail code word & retrieve previous one
@@ -236,7 +240,7 @@ static __always_inline u32 xchg_tail(struct qspinlock *lock, u32 tail) } return old; } -#endif /* _Q_PENDING_BITS == 8 */ +#endif /** * queued_fetch_set_pending_acquire - fetch the whole lock value and set pending
--
2.17.1