![Peter Zijlstra](/assets/img/avatar_default.png)
Effective revert commit:
87709e28dc
("fs/locks: Use percpu_down_read_preempt_disable()")
This is causing major pain for PREEMPT_RT.
Sebastian did a lot of lockperf runs on 2 and 4 node machines with all
preemption modes (PREEMPT=n should be an obvious NOP for this patch
and thus serves as a good control) and no results showed significance
over 2-sigma (the PREEMPT=n results were almost empty at 1-sigma).
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
135 lines
3.7 KiB
C
135 lines
3.7 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_PERCPU_RWSEM_H
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#define _LINUX_PERCPU_RWSEM_H
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#include <linux/atomic.h>
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#include <linux/rwsem.h>
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#include <linux/percpu.h>
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#include <linux/rcuwait.h>
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#include <linux/rcu_sync.h>
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#include <linux/lockdep.h>
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struct percpu_rw_semaphore {
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struct rcu_sync rss;
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unsigned int __percpu *read_count;
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struct rw_semaphore rw_sem; /* slowpath */
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struct rcuwait writer; /* blocked writer */
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int readers_block;
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};
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#define DEFINE_STATIC_PERCPU_RWSEM(name) \
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static DEFINE_PER_CPU(unsigned int, __percpu_rwsem_rc_##name); \
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static struct percpu_rw_semaphore name = { \
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.rss = __RCU_SYNC_INITIALIZER(name.rss, RCU_SCHED_SYNC), \
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.read_count = &__percpu_rwsem_rc_##name, \
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.rw_sem = __RWSEM_INITIALIZER(name.rw_sem), \
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.writer = __RCUWAIT_INITIALIZER(name.writer), \
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}
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extern int __percpu_down_read(struct percpu_rw_semaphore *, int);
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extern void __percpu_up_read(struct percpu_rw_semaphore *);
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static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
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{
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might_sleep();
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rwsem_acquire_read(&sem->rw_sem.dep_map, 0, 0, _RET_IP_);
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preempt_disable();
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/*
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* We are in an RCU-sched read-side critical section, so the writer
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* cannot both change sem->state from readers_fast and start checking
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* counters while we are here. So if we see !sem->state, we know that
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* the writer won't be checking until we're past the preempt_enable()
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* and that once the synchronize_rcu() is done, the writer will see
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* anything we did within this RCU-sched read-size critical section.
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*/
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__this_cpu_inc(*sem->read_count);
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if (unlikely(!rcu_sync_is_idle(&sem->rss)))
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__percpu_down_read(sem, false); /* Unconditional memory barrier */
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/*
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* The preempt_enable() prevents the compiler from
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* bleeding the critical section out.
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*/
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preempt_enable();
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}
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static inline int percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
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{
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int ret = 1;
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preempt_disable();
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/*
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* Same as in percpu_down_read().
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*/
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__this_cpu_inc(*sem->read_count);
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if (unlikely(!rcu_sync_is_idle(&sem->rss)))
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ret = __percpu_down_read(sem, true); /* Unconditional memory barrier */
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preempt_enable();
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/*
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* The barrier() from preempt_enable() prevents the compiler from
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* bleeding the critical section out.
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*/
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if (ret)
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rwsem_acquire_read(&sem->rw_sem.dep_map, 0, 1, _RET_IP_);
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return ret;
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}
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static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
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{
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preempt_disable();
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/*
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* Same as in percpu_down_read().
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*/
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if (likely(rcu_sync_is_idle(&sem->rss)))
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__this_cpu_dec(*sem->read_count);
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else
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__percpu_up_read(sem); /* Unconditional memory barrier */
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preempt_enable();
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rwsem_release(&sem->rw_sem.dep_map, 1, _RET_IP_);
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}
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extern void percpu_down_write(struct percpu_rw_semaphore *);
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extern void percpu_up_write(struct percpu_rw_semaphore *);
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extern int __percpu_init_rwsem(struct percpu_rw_semaphore *,
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const char *, struct lock_class_key *);
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extern void percpu_free_rwsem(struct percpu_rw_semaphore *);
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#define percpu_init_rwsem(sem) \
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({ \
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static struct lock_class_key rwsem_key; \
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__percpu_init_rwsem(sem, #sem, &rwsem_key); \
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})
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#define percpu_rwsem_is_held(sem) lockdep_is_held(&(sem)->rw_sem)
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#define percpu_rwsem_assert_held(sem) \
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lockdep_assert_held(&(sem)->rw_sem)
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static inline void percpu_rwsem_release(struct percpu_rw_semaphore *sem,
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bool read, unsigned long ip)
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{
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lock_release(&sem->rw_sem.dep_map, 1, ip);
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#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
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if (!read)
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sem->rw_sem.owner = RWSEM_OWNER_UNKNOWN;
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#endif
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}
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static inline void percpu_rwsem_acquire(struct percpu_rw_semaphore *sem,
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bool read, unsigned long ip)
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{
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lock_acquire(&sem->rw_sem.dep_map, 0, 1, read, 1, NULL, ip);
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#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
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if (!read)
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sem->rw_sem.owner = current;
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#endif
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}
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#endif
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