From 73d0f37ac4ee5b60e6b9c1b3ccb8766bade9d9c5 Mon Sep 17 00:00:00 2001 From: Vasily Averin Date: Thu, 14 Aug 2014 12:27:47 +0400 Subject: [PATCH] cbq: incorrectly low bandwidth setting blocks limited traffic Mainstream commit f0f6ee1f70c4 ("cbq: incorrect processing of high limits") have side effect: if cbq bandwidth setting is less than real interface throughput non-limited traffic can delay limited traffic for a very long time. This happen because of q->now changes incorrectly in cbq_dequeue(): in described scenario L2T is much greater than real time delay, and q->now gets an extra boost for each transmitted packet. Accumulated boost prevents update q->now, and blocked class can wait very long time until (q->now >= cl->undertime) will be true again. To fix the problem the patch updates q->now on each cbq_update() call. L2T-related pre-modification q->now was moved to cbq_update(). My testing confirmed that it fixes the problem and did not discover any side-effects Fixes: f0f6ee1f70c4 ("cbq: incorrect processing of high limits") Signed-off-by: Vasily Averin Signed-off-by: David S. Miller --- net/sched/sch_cbq.c | 35 ++++++++++++----------------------- 1 file changed, 12 insertions(+), 23 deletions(-) diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c index ead526467cca..550be9504fff 100644 --- a/net/sched/sch_cbq.c +++ b/net/sched/sch_cbq.c @@ -700,8 +700,13 @@ cbq_update(struct cbq_sched_data *q) struct cbq_class *this = q->tx_class; struct cbq_class *cl = this; int len = q->tx_len; + psched_time_t now; q->tx_class = NULL; + /* Time integrator. We calculate EOS time + * by adding expected packet transmission time. + */ + now = q->now + L2T(&q->link, len); for ( ; cl; cl = cl->share) { long avgidle = cl->avgidle; @@ -717,7 +722,7 @@ cbq_update(struct cbq_sched_data *q) * idle = (now - last) - last_pktlen/rate */ - idle = q->now - cl->last; + idle = now - cl->last; if ((unsigned long)idle > 128*1024*1024) { avgidle = cl->maxidle; } else { @@ -761,7 +766,7 @@ cbq_update(struct cbq_sched_data *q) idle -= L2T(&q->link, len); idle += L2T(cl, len); - cl->undertime = q->now + idle; + cl->undertime = now + idle; } else { /* Underlimit */ @@ -771,7 +776,8 @@ cbq_update(struct cbq_sched_data *q) else cl->avgidle = avgidle; } - cl->last = q->now; + if ((s64)(now - cl->last) > 0) + cl->last = now; } cbq_update_toplevel(q, this, q->tx_borrowed); @@ -943,30 +949,13 @@ cbq_dequeue(struct Qdisc *sch) struct sk_buff *skb; struct cbq_sched_data *q = qdisc_priv(sch); psched_time_t now; - psched_tdiff_t incr; now = psched_get_time(); - incr = now - q->now_rt; - if (q->tx_class) { - psched_tdiff_t incr2; - /* Time integrator. We calculate EOS time - * by adding expected packet transmission time. - * If real time is greater, we warp artificial clock, - * so that: - * - * cbq_time = max(real_time, work); - */ - incr2 = L2T(&q->link, q->tx_len); - q->now += incr2; + if (q->tx_class) cbq_update(q); - if ((incr -= incr2) < 0) - incr = 0; - q->now += incr; - } else { - if (now > q->now) - q->now = now; - } + + q->now = now; q->now_rt = now; for (;;) {