From a5d28090405038ca1f40c13f38d6d4285456efee Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Thu, 30 Apr 2015 09:40:40 -0700 Subject: [PATCH] codel: fix maxpacket/mtu confusion 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 Cc: Kathleen Nichols Cc: Dave Taht Cc: Van Jacobson Signed-off-by: David S. Miller --- 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 aeee28081245..1e18005f7f65 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 de28f8e968e8..7a0bdb16ac92 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 1e52decb7b59..c244c45b78d7 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; -- 2.20.1