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Date: Sat, 28 Nov 2009 01:04:01 +0100 From: Jarek Poplawski <jarkao2@...il.com> To: xiaosuo@...il.com Cc: Jamal Hadi Salim <hadi@...erus.ca>, "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org Subject: Re: [PATCH] sch_htb: ix the deficit overflows Changli Gao wrote, On 11/27/2009 09:14 AM: > fix the deficit overflows. > > HTB uses WDRR(Weighted Deficit Round Robin) algorithm to schedule the spare > bandwidth, but it doesn't check if the deficit is big enough for the skb when > dequeuing skb from a class. In some case(the quantum is smaller than the > packet size), the deficit will be decreased, even when it is smaller than > ZERO. At last, the deficit will overflows, and become MAX_INT. This case of the quantum smaller than the packet size should be treated as a broken config, so I don't think it's worth to do such a deep change with additional delays and cpu cycles for all to fix it. A warning or lower limit should be enough (if necessary at all). Jarek P. > > Signed-off-by: Changli Gao <xiaosuo@...il.com> > ---- > sch_htb.c | 25 ++++++++++++++++++++----- > 1 file changed, 20 insertions(+), 5 deletions(-) > diff --git a/net/sched/sch_htb.c b/net/sched/sch_htb.c > index 2e38d1a..293983e 100644 > --- a/net/sched/sch_htb.c > +++ b/net/sched/sch_htb.c > @@ -783,6 +783,7 @@ static struct sk_buff *htb_dequeue_tree(struct htb_sched *q, int prio, > { > struct sk_buff *skb = NULL; > struct htb_class *cl, *start; > + unsigned int len; > /* look initial class up in the row */ > start = cl = htb_lookup_leaf(q->row[level] + prio, prio, > q->ptr[level] + prio, > @@ -815,9 +816,23 @@ next: > goto next; > } > > - skb = cl->un.leaf.q->dequeue(cl->un.leaf.q); > - if (likely(skb != NULL)) > - break; > + skb = cl->un.leaf.q->ops->peek(cl->un.leaf.q); > + if (likely(skb != NULL)) { > + len = qdisc_pkt_len(skb); > + if (len <= cl->un.leaf.deficit[level]) { > + skb = qdisc_dequeue_peeked(cl->un.leaf.q); > + break; > + } > + skb = NULL; > + cl->un.leaf.deficit[level] += cl->quantum; > + htb_next_rb_node((level ? cl->parent->un.inner.ptr : > + q->ptr[0]) + prio); > + cl = htb_lookup_leaf(q->row[level] + prio, prio, > + q->ptr[level] + prio, > + q->last_ptr_id[level] + prio); > + start = cl; > + goto next; > + } > > qdisc_warn_nonwc("htb", cl->un.leaf.q); > htb_next_rb_node((level ? cl->parent->un.inner.ptr : q-> > @@ -829,8 +844,8 @@ next: > } while (cl != start); > > if (likely(skb != NULL)) { > - cl->un.leaf.deficit[level] -= qdisc_pkt_len(skb); > - if (cl->un.leaf.deficit[level] < 0) { > + cl->un.leaf.deficit[level] -= len; > + if (cl->un.leaf.deficit[level] <= 0) { > cl->un.leaf.deficit[level] += cl->quantum; > htb_next_rb_node((level ? cl->parent->un.inner.ptr : q-> > ptr[0]) + prio); > > -- -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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