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

John Fastabend
2016-07-15T17:30:09Z

On 16-07-15 03:09 AM, Jesper Dangaard Brouer wrote:
> 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...
>

hah I was agreeing with you as in yep no need for the _bh variant :)
I must have been low on coffee or something when I wrote that response
because when I read it now it sounds like I really think the _bh is
needed.

At any rate _bh removed thanks!