From: Eric Dumazet <eduma...@google.com>
Under presence of TSO/GSO/GRO packets, codel at low rates can be quite
useless. In following example, not a single packet was ever dropped,
while average delay in codel queue is ~100 ms !
qdisc codel 0: parent 1:12 limit 16000p target 5.0ms interval 100.0ms
Sent 134376498 bytes 88797 pkt (dropped 0, overlimits 0 requeues 0)
backlog 13626b 3p requeues 0
count 0 lastcount 0 ldelay 96.9ms drop_next 0us
maxpacket 9084 ecn_mark 0 drop_overlimit 0
This comes from a confusion of what should be the minimal backlog. It is
pretty clear it is not 64KB or whatever max GSO packet ever reached the
qdisc.
codel intent was to use MTU of the device.
After the fix, we finally drop some packets, and rtt/cwnd of my single
TCP flow are meeting our expectations.
qdisc codel 0: parent 1:12 limit 16000p target 5.0ms interval 100.0ms
Sent 102798497 bytes 67912 pkt (dropped 1365, overlimits 0 requeues 0)
backlog 6056b 3p requeues 0
count 1 lastcount 1 ldelay 36.3ms drop_next 0us
maxpacket 10598 ecn_mark 0 drop_overlimit 0
Signed-off-by: Eric Dumazet <eduma...@google.com>
Cc: Kathleen Nichols <nich...@pollere.com>
Cc: Dave Taht <dave.t...@gmail.com>
Cc: Van Jacobson <v...@google.com>
---
include/net/codel.h | 10 +++++++---
net/sched/sch_codel.c | 2 +-
net/sched/sch_fq_codel.c | 2 +-
3 files changed, 9 insertions(+), 5 deletions(-)
diff --git a/include/net/codel.h b/include/net/codel.h
index
aeee28081245c9215f10badd611f58ba0124fcd0..1e18005f7f65f061f6084ea1823a8d37368a57e4
100644
--- a/include/net/codel.h
+++ b/include/net/codel.h
@@ -120,11 +120,13 @@ static inline u32 codel_time_to_us(codel_time_t val)
* struct codel_params - contains codel parameters
* @target: target queue size (in time units)
* @interval: width of moving time window
+ * @mtu: device mtu, or minimal queue backlog in bytes.
* @ecn: is Explicit Congestion Notification enabled
*/
struct codel_params {
codel_time_t target;
codel_time_t interval;
+ u32 mtu;
bool ecn;
};
@@ -166,10 +168,12 @@ struct codel_stats {
u32 ecn_mark;
};
-static void codel_params_init(struct codel_params *params)
+static void codel_params_init(struct codel_params *params,
+ const struct Qdisc *sch)
{
params->interval = MS2TIME(100);
params->target = MS2TIME(5);
+ params->mtu = psched_mtu(qdisc_dev(sch));
params->ecn = false;
}
@@ -180,7 +184,7 @@ static void codel_vars_init(struct codel_vars *vars)
static void codel_stats_init(struct codel_stats *stats)
{
- stats->maxpacket = 256;
+ stats->maxpacket = 0;
}
/*
@@ -234,7 +238,7 @@ static bool codel_should_drop(const struct sk_buff *skb,
stats->maxpacket = qdisc_pkt_len(skb);
if (codel_time_before(vars->ldelay, params->target) ||
- sch->qstats.backlog <= stats->maxpacket) {
+ sch->qstats.backlog <= params->mtu) {
/* went below - stay below for at least interval */
vars->first_above_time = 0;
return false;
diff --git a/net/sched/sch_codel.c b/net/sched/sch_codel.c
index
de28f8e968e8176ac7630a1e6fcccb45ad295f5d..7a0bdb16ac92fd0a20f565295392bed8674c8d90
100644
--- a/net/sched/sch_codel.c
+++ b/net/sched/sch_codel.c
@@ -164,7 +164,7 @@ static int codel_init(struct Qdisc *sch, struct nlattr *opt)
sch->limit = DEFAULT_CODEL_LIMIT;
- codel_params_init(&q->params);
+ codel_params_init(&q->params, sch);
codel_vars_init(&q->vars);
codel_stats_init(&q->stats);
diff --git a/net/sched/sch_fq_codel.c b/net/sched/sch_fq_codel.c
index
1e52decb7b59cf0b4173d0f17efdab8fefee5f26..c244c45b78d7feca32fda3b925f7605aebf0a5b6
100644
--- a/net/sched/sch_fq_codel.c
+++ b/net/sched/sch_fq_codel.c
@@ -391,7 +391,7 @@ static int fq_codel_init(struct Qdisc *sch, struct nlattr
*opt)
q->perturbation = prandom_u32();
INIT_LIST_HEAD(&q->new_flows);
INIT_LIST_HEAD(&q->old_flows);
- codel_params_init(&q->cparams);
+ codel_params_init(&q->cparams, sch);
codel_stats_init(&q->cstats);
q->cparams.ecn = true;
--
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