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Commit 73d0f37a authored by Vasily Averin's avatar Vasily Averin Committed by David S. Miller
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cbq: incorrectly low bandwidth setting blocks limited traffic 



Mainstream commit f0f6ee1f ("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: f0f6ee1f ("cbq: incorrect processing of high limits")

Signed-off-by: default avatarVasily Averin <vvs@openvz.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent ac32c7f7

net/sched/sch_cbq.c

+13 −24
Original line number Diff line number Diff line
@@ -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_rt = now;



	for (;;) {