Re: [PATCH v3 2/5] locking/qspinlock: Refactor the qspinlock slow path

[Peter Zijlstra]

On Mon, Jul 15, 2019 at 03:25:33PM -0400, Alex Kogan wrote:

> +/*
> + * set_locked_empty_mcs - Try to set the spinlock value to _Q_LOCKED_VAL,
> + * and by doing that unlock the MCS lock when its waiting queue is empty
> + * @lock: Pointer to queued spinlock structure
> + * @val: Current value of the lock
> + * @node: Pointer to the MCS node of the lock holder
> + *
> + * *,*,* -> 0,0,1
> + */
> +static __always_inline bool __set_locked_empty_mcs(struct qspinlock *lock,
> +						   u32 val,
> +						   struct mcs_spinlock *node)
> +{
> +	return atomic_try_cmpxchg_relaxed(&lock->val, &val, _Q_LOCKED_VAL);
> +}

That name is nonsense. It should be something like:

static __always_inline bool __try_clear_tail(...)


> +/*
> + * pass_mcs_lock - pass the MCS lock to the next waiter
> + * @node: Pointer to the MCS node of the lock holder
> + * @next: Pointer to the MCS node of the first waiter in the MCS queue
> + */
> +static __always_inline void __pass_mcs_lock(struct mcs_spinlock *node,
> +					    struct mcs_spinlock *next)
> +{
> +	arch_mcs_spin_unlock_contended(&next->locked, 1);
> +}

I'm not entirely happy with that name either; but it's not horrible like
the other one. Why not mcs_spin_unlock_contended() ?