[ofa-general] Re: [PATCH 3/9 Rev3] [sched] Modify qdisc_run to support batching

Evgeniy Polyakov
2007-08-08T12:14:02Z

On Wed, Aug 08, 2007 at 03:01:45PM +0530, Krishna Kumar (krkumar2@in.ibm.com) wrote:
> +static inline int get_skb(struct net_device *dev, struct Qdisc *q,
> + struct sk_buff_head *blist, struct sk_buff **skbp)
> +{
> + if (likely(!blist || (!skb_queue_len(blist) && qdisc_qlen(q) <= 1))) {
> + return likely((*skbp = dev_dequeue_skb(dev, q)) != NULL);
> + } else {
> + int max = dev->tx_queue_len - skb_queue_len(blist);
> + struct sk_buff *skb;
> +
> + while (max > 0 && (skb = dev_dequeue_skb(dev, q)) != NULL)
> + max -= dev_add_skb_to_blist(skb, dev);
> +
> + *skbp = NULL;
> + return 1; /* we have atleast one skb in blist */
> + }
> +}

Same here - is it possible to get a list in one go instead of pulling
one-by-one, since it forces quite a few additional unneded lock
get/releases. What about dev_dequeue_number_skb(dev, q, num), which will
grab the lock and move a list of skbs from one queue to provided head.

> @@ -158,7 +198,10 @@ static inline int qdisc_restart(struct n
> /* And release queue */
> spin_unlock(&dev->queue_lock);
>
> - ret = dev_hard_start_xmit(skb, dev);
> + if (likely(skb))
> + ret = dev_hard_start_xmit(skb, dev);
> + else
> + ret = dev->hard_start_xmit_batch(dev);

Perfectionism says that having array of two functions and calling one of
them via array_func_pointer[!!skb] will be much faster. Just a though.
It is actually much faster than if/else on x86 at least.

--
Evgeniy Polyakov