Possible eHEA performance issue

    if (unlikely(atomic_read(&pr->swqe_avail) <= 1)) {
	    spin_lock_irqsave(&pr->netif_queue, flags);
	    if (unlikely(atomic_read(&pr->swqe_avail) <= 1)) {
		    pr->p_stats.queue_stopped++;
		    netif_stop_queue(dev);
		    pr->queue_stopped = 1;
	    }
	    spin_unlock_irqrestore(&pr->netif_queue, flags);
    }

Since the conditions are the same, isn't it likely that the second 'if' is going to be taken. Hence, shouldn't the second 'unlikely' hint be removed or even changed to likely?

Either way, some documentation here as to why it's done this way would be useful. I assume the atomic_read is cheap compared to the spin_unlock_irqsave, so we quickly check swqe_avail before we check it again properly with the lock on so we can change some stuff.

Mikey

Hi Mike,

good point the second if could be a likely(). The impact isn't that big because the if statement is true in the unlikely() case that the send queue is full - which doesn't happen often. Anyway we will modify this in one of the next driver versions. Thanks for the hint!

Thomas