Re: [RFC PATCH v2 08/10] net: sched: pfifo_fast use alf_queue

Jesper Dangaard Brouer
2016-07-15T10:09:41Z

On Thu, 14 Jul 2016 17:09:43 -0700
John Fastabend <john.fastabend@gmail.com> wrote:

> >> static int pfifo_fast_enqueue(struct sk_buff *skb, struct Qdisc *qdisc,
> >> struct sk_buff **to_free)
> >> {
> >> - if (skb_queue_len(&qdisc->q) < qdisc_dev(qdisc)->tx_queue_len) {
> >> - int band = prio2band[skb->priority & TC_PRIO_MAX];
> >> - struct pfifo_fast_priv *priv = qdisc_priv(qdisc);
> >> - struct sk_buff_head *list = band2list(priv, band);
> >> -
> >> - priv->bitmap |= (1 << band);
> >> - qdisc->q.qlen++;
> >> - return __qdisc_enqueue_tail(skb, qdisc, list);
> >> - }
> >> + int band = prio2band[skb->priority & TC_PRIO_MAX];
> >> + struct pfifo_fast_priv *priv = qdisc_priv(qdisc);
> >> + struct skb_array *q = band2list(priv, band);
> >> + int err;
> >>
> >> - return qdisc_drop(skb, qdisc, to_free);
> >> + err = skb_array_produce_bh(q, skb);
> >
> > Do you need the _bh variant here? (Doesn't the qdisc run with BH disabled?)
> >
> >
>
> Yep its inside rcu_read_lock_bh().

The call rcu_read_lock_bh() already disabled BH (local_bh_disable()).
Thus, you can use the normal variants of skb_array_produce(), it is
(approx 20 cycles) faster than the _bh variant...

--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
Author of http://www.iptv-analyzer.org
LinkedIn: http://www.linkedin.com/in/brouer