mirror of
https://github.com/torvalds/linux.git
synced 2024-11-10 14:11:52 +00:00
aa65ff6b18
These have shown significantly improved performance and fairness when spinlock contention is moderate to high on very large systems. With this series including subsequent patches, on a 16 socket 1536 thread POWER9, a stress test such as same-file open/close from all CPUs gets big speedups, 11620op/s aggregate with simple spinlocks vs 384158op/s (33x faster), where the difference in throughput between the fastest and slowest thread goes from 7x to 1.4x. Thanks to the fast path being identical in terms of atomics and barriers (after a subsequent optimisation patch), single threaded performance is not changed (no measurable difference). On smaller systems, performance and fairness seems to be generally improved. Using dbench on tmpfs as a test (that starts to run into kernel spinlock contention), a 2-socket OpenPOWER POWER9 system was tested with bare metal and KVM guest configurations. Results can be found here: https://github.com/linuxppc/issues/issues/305#issuecomment-663487453 Observations are: - Queued spinlocks are equal when contention is insignificant, as expected and as measured with microbenchmarks. - When there is contention, on bare metal queued spinlocks have better throughput and max latency at all points. - When virtualised, queued spinlocks are slightly worse approaching peak throughput, but significantly better throughput and max latency at all points beyond peak, until queued spinlock maximum latency rises when clients are 2x vCPUs. The regressions haven't been analysed very well yet, there are a lot of things that can be tuned, particularly the paravirtualised locking, but the numbers already look like a good net win even on relatively small systems. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Waiman Long <longman@redhat.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20200724131423.1362108-4-npiggin@gmail.com
119 lines
3.2 KiB
C
119 lines
3.2 KiB
C
/* SPDX-License-Identifier: GPL-2.0-or-later */
|
|
/*
|
|
* Queued spinlock
|
|
*
|
|
* (C) Copyright 2013-2015 Hewlett-Packard Development Company, L.P.
|
|
* (C) Copyright 2015 Hewlett-Packard Enterprise Development LP
|
|
*
|
|
* Authors: Waiman Long <waiman.long@hpe.com>
|
|
*/
|
|
#ifndef __ASM_GENERIC_QSPINLOCK_H
|
|
#define __ASM_GENERIC_QSPINLOCK_H
|
|
|
|
#include <asm-generic/qspinlock_types.h>
|
|
|
|
#ifndef queued_spin_is_locked
|
|
/**
|
|
* queued_spin_is_locked - is the spinlock locked?
|
|
* @lock: Pointer to queued spinlock structure
|
|
* Return: 1 if it is locked, 0 otherwise
|
|
*/
|
|
static __always_inline int queued_spin_is_locked(struct qspinlock *lock)
|
|
{
|
|
/*
|
|
* Any !0 state indicates it is locked, even if _Q_LOCKED_VAL
|
|
* isn't immediately observable.
|
|
*/
|
|
return atomic_read(&lock->val);
|
|
}
|
|
#endif
|
|
|
|
/**
|
|
* queued_spin_value_unlocked - is the spinlock structure unlocked?
|
|
* @lock: queued spinlock structure
|
|
* Return: 1 if it is unlocked, 0 otherwise
|
|
*
|
|
* N.B. Whenever there are tasks waiting for the lock, it is considered
|
|
* locked wrt the lockref code to avoid lock stealing by the lockref
|
|
* code and change things underneath the lock. This also allows some
|
|
* optimizations to be applied without conflict with lockref.
|
|
*/
|
|
static __always_inline int queued_spin_value_unlocked(struct qspinlock lock)
|
|
{
|
|
return !atomic_read(&lock.val);
|
|
}
|
|
|
|
/**
|
|
* queued_spin_is_contended - check if the lock is contended
|
|
* @lock : Pointer to queued spinlock structure
|
|
* Return: 1 if lock contended, 0 otherwise
|
|
*/
|
|
static __always_inline int queued_spin_is_contended(struct qspinlock *lock)
|
|
{
|
|
return atomic_read(&lock->val) & ~_Q_LOCKED_MASK;
|
|
}
|
|
/**
|
|
* queued_spin_trylock - try to acquire the queued spinlock
|
|
* @lock : Pointer to queued spinlock structure
|
|
* Return: 1 if lock acquired, 0 if failed
|
|
*/
|
|
static __always_inline int queued_spin_trylock(struct qspinlock *lock)
|
|
{
|
|
u32 val = atomic_read(&lock->val);
|
|
|
|
if (unlikely(val))
|
|
return 0;
|
|
|
|
return likely(atomic_try_cmpxchg_acquire(&lock->val, &val, _Q_LOCKED_VAL));
|
|
}
|
|
|
|
extern void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
|
|
|
|
/**
|
|
* queued_spin_lock - acquire a queued spinlock
|
|
* @lock: Pointer to queued spinlock structure
|
|
*/
|
|
static __always_inline void queued_spin_lock(struct qspinlock *lock)
|
|
{
|
|
u32 val = 0;
|
|
|
|
if (likely(atomic_try_cmpxchg_acquire(&lock->val, &val, _Q_LOCKED_VAL)))
|
|
return;
|
|
|
|
queued_spin_lock_slowpath(lock, val);
|
|
}
|
|
|
|
#ifndef queued_spin_unlock
|
|
/**
|
|
* queued_spin_unlock - release a queued spinlock
|
|
* @lock : Pointer to queued spinlock structure
|
|
*/
|
|
static __always_inline void queued_spin_unlock(struct qspinlock *lock)
|
|
{
|
|
/*
|
|
* unlock() needs release semantics:
|
|
*/
|
|
smp_store_release(&lock->locked, 0);
|
|
}
|
|
#endif
|
|
|
|
#ifndef virt_spin_lock
|
|
static __always_inline bool virt_spin_lock(struct qspinlock *lock)
|
|
{
|
|
return false;
|
|
}
|
|
#endif
|
|
|
|
/*
|
|
* Remapping spinlock architecture specific functions to the corresponding
|
|
* queued spinlock functions.
|
|
*/
|
|
#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)
|
|
|
|
#endif /* __ASM_GENERIC_QSPINLOCK_H */
|