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Date: Thu, 14 Aug 2014 12:27:47 +0400 From: Vasily Averin <vvs@...allels.com> To: netdev@...r.kernel.org, Jamal Hadi Salim <jhs@...atatu.com>, "David S. Miller" <davem@...emloft.net> CC: Eric Dumazet <eric.dumazet@...il.com>, Alexey Kuznetsov <kuznet@....inr.ac.ru> Subject: [PATCH net v2 1/2] 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 <vvs@...nvz.org> --- net/sched/sch_cbq.c | 37 +++++++++++++------------------------ 1 files changed, 13 insertions(+), 24 deletions(-) diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c index ead5264..550be95 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 (;;) { -- 1.7.1 -- 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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