search for: _qspinlock_locked_slowpath

...nlock code that is used when PV spinlock is enabled. The right unlock code is if (static_key_false(&paravirt_spinlocks_enabled)) { /* * Need to atomically clear the lock byte to avoid racing with * queue head waiter trying to set _QSPINLOCK_LOCKED_SLOWPATH. */ if (likely(cmpxchg(&qlock->lock, _QSPINLOCK_LOCKED, 0) == _QSPINLOCK_LOCKED)) return; else queue_spin_unlock_slowpath(lock); } else {...

...nlock code that is used when PV spinlock is enabled. The right unlock code is if (static_key_false(&paravirt_spinlocks_enabled)) { /* * Need to atomically clear the lock byte to avoid racing with * queue head waiter trying to set _QSPINLOCK_LOCKED_SLOWPATH. */ if (likely(cmpxchg(&qlock->lock, _QSPINLOCK_LOCKED, 0) == _QSPINLOCK_LOCKED)) return; else queue_spin_unlock_slowpath(lock); } else {...

...spins 2*QSPIN_THRESHOLD times before halting itself. When it has spinned QSPIN_THRESHOLD times, the queue head will assume that the lock holder may be scheduled out and attempt to kick the lock holder CPU if it has the CPU number on hand. Before being halted, the queue head waiter will set a flag (_QSPINLOCK_LOCKED_SLOWPATH) in the lock byte to indicate that the unlock slowpath has to be invoked. In the unlock slowpath, the current lock holder will find the queue head by following the previous node pointer links stored in the queue node structure until it finds one that has the wait flag turned off. It then attempt t...

On 12/03/14 18:54, Waiman Long wrote: > This patch adds para-virtualization support to the queue spinlock in > the same way as was done in the PV ticket lock code. In essence, the > lock waiters will spin for a specified number of times (QSPIN_THRESHOLD > = 2^14) and then halted itself. The queue head waiter will spins > 2*QSPIN_THRESHOLD times before halting itself. When it has

On 12/03/14 18:54, Waiman Long wrote: > This patch adds para-virtualization support to the queue spinlock in > the same way as was done in the PV ticket lock code. In essence, the > lock waiters will spin for a specified number of times (QSPIN_THRESHOLD > = 2^14) and then halted itself. The queue head waiter will spins > 2*QSPIN_THRESHOLD times before halting itself. When it has

...ACCESS_ONCE(pv->cpustate) = PV_CPU_KICKED; __queue_kick_cpu(pv->mycpu, PV_KICK_QUEUE_HEAD); Waiter ------------------------------------------- // pv_head_spin_check ACCESS_ONCE(pv->cpustate) = PV_CPU_HALTED; lockval = cmpxchg(&qlock->lock, _QSPINLOCK_LOCKED, _QSPINLOCK_LOCKED_SLOWPATH); if (lockval == 0) { /* * Can exit now as the lock is free */ ACCESS_ONCE(pv->cpustate) = PV_CPU_ACTIVE; *count = 0; return; } __queue_hibernate(); Nothing protects from writing qlock->lock before pv->cpustate is read, leading to this: Lock holder Waiter -...

v5->v6: - Change the optimized 2-task contending code to make it fairer at the expense of a bit of performance. - Add a patch to support unfair queue spinlock for Xen. - Modify the PV qspinlock code to follow what was done in the PV ticketlock. - Add performance data for the unfair lock as well as the PV support code. v4->v5: - Move the optimized 2-task contending code to the

v5->v6: - Change the optimized 2-task contending code to make it fairer at the expense of a bit of performance. - Add a patch to support unfair queue spinlock for Xen. - Modify the PV qspinlock code to follow what was done in the PV ticketlock. - Add performance data for the unfair lock as well as the PV support code. v4->v5: - Move the optimized 2-task contending code to the