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@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
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 @@
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 @@
* 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 @@
idle -= L2T(&q->link, len);
idle += L2T(cl, len);
- cl->undertime = q->now + idle;
+ cl->undertime = now + idle;
} else {
/* Underlimit */
@@ -771,7 +776,8 @@
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 @@
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 (;;) {