Subject: Re: [PATCH v2] net_sched: sch_sfq: fix allot handling

From: Patrick McHardy <[email-masked]>
Date: Wed, 15 Dec 2010 18:03:48 +0100

On 15.12.2010 17:55, Eric Dumazet wrote:
> Le mercredi 15 décembre 2010 à 17:43 +0100, Patrick McHardy a écrit :
> 
>> Now we could remove the allot increase in sfq_dequeue for
>> the case that the flow becomes inactive. It is incorrect
>> anyways.
> 
> Hmm, we increase the allot for the next slot, not for the slot now
> empty.
> 
> 
>         /* Is the slot empty? */
>         if (q->qs[a].qlen == 0) {
>                 q->ht[q->hash[a]] = SFQ_DEPTH;
>                 a = q->next[a]; // a = next slot index
>                 if (a == old_a) {
>                         q->tail = SFQ_DEPTH;
>                         return skb;
>                 }
>                 q->next[q->tail] = a;
>                 q->allot[a] += q->quantum;
> // HERE, q->allot[a] is for next slot, we give it its quantum for being
> activated

Right, that's odd. It shouldn't be necessary anymore though since
now we initialize allot in sfq_enqueue() for all new flows and
increase allotment for all active flows once per round in sfq_dequeue().
The above code causes a second increase for the flow following a flow
which went inactive.

> 
>         } else if ((q->allot[a] -= qdisc_pkt_len(skb)) <= 0) {
> 
> Maybe we should rename (a / old_a) by (a / next_a) to avoid confusion :)

That might have made things more clearer :)

> I was thinking in allowing more packets per SFQ (but keep the 126 active
> flows limit), what do you think ?

I keep forgetting why this limit exists, let me try to figure
it out once more :)