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cbq: incorrectly low bandwidth setting blocks limited traffic 

Mainstream commit f0f6ee1f70 ("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: f0f6ee1f70 ("cbq: incorrect processing of high limits")

Signed-off-by: Vasily Averin <vvs@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Vasily Averin 2014-08-14 12:27:47 +04:00 committed by David S. Miller
parent ac32c7f705
commit 73d0f37ac4
1 changed files with 12 additions and 23 deletions
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33
net/sched/sch_cbq.c
View File

@ -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 (;;) {