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SubjectRe: [PATCH] pkt_sched: QFQ Plus: fair-queueing service at DRR cost
Il 20/11/2012 19:54, David Miller ha scritto:
> From: Paolo Valente <paolo.valente@unimore.it>
> Date: Tue, 20 Nov 2012 18:45:13 +0100
>
>> - struct sk_buff *skb;
>> + struct sk_buff *skb = NULL;
>
> This is not really an improvement,
Sorry for trying this silly short cut
now the compiler can think
> that NULL is passed eventually into qdisc_bstats_update().
>
> Please make the logic easier for the compiler to digest.
>
> For example, restructure the top-level logic into something like:
>
> skb = NULL;
> if (!list_empty(&in_serv_agg->active))
> skb = qfq_peek_skb(in_serv_agg, &cl, &len);
> else
> len = 0; /* no more active classes in the in-service agg */
>
> if (len == 0 || in_serv_agg->budget < len) {
> ...
> /*
> * If we get here, there are other aggregates queued:
> * choose the new aggregate to serve.
> */
> in_serv_agg = q->in_serv_agg = qfq_choose_next_agg(q);
> skb = qfq_peek_skb(in_serv_agg, &cl, &len);
> }
> if (!skb)
> return NULL;
>
> That way it is clearer, to both humans and the compiler, what is
> going on here.
>
Got it. Actually, if the first qfq_peek_skb returns NULL, then the
example version that you are proposing apparently may behave in a
different way than the original one: in your proposal the scheduler
tries to switch to a new aggregate and may return a non-NULL value,
whereas the original version would immediately return NULL. I guess that
this slightly different behavior is fine as well, and I am preparing a
new patch that integrates these changes.
> Thanks.
>


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| Paolo Valente | |
| Algogroup | |
| Dip. Ing. Informazione | tel: +39 059 2056318 |
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| 41125 Modena - Italy | |
| home: http://algo.ing.unimo.it/people/paolo/ |
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