Re: [PATCH 1/2] block/mq-deadline: serialize request dispatching

[Bart Van Assche <bvanassche@acm.org>]

On 1/18/24 10:45, Jens Axboe wrote:
> Do you read the replies to the emails, from the other thread?

Yes.
  > And secondly, this avoids a RMW if it's already set.
 From the spinlock implementation (something I looked up before I wrote
my previous reply):

static __always_inline int queued_spin_trylock(struct qspinlock *lock)
{
	int val = atomic_read(&lock->val);

	if (unlikely(val))
		return 0;

	return likely(atomic_try_cmpxchg_acquire(&lock->val, &val,
                                                  _Q_LOCKED_VAL));
}

I think this implementation does not perform a RMW if the spinlock is
already locked.

Thanks,

Bart.