luck/tmp_suning_uos_patched
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codel: fix maxpacket/mtu confusion

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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 <edumazet@google.com>
Cc: Kathleen Nichols <nichols@pollere.com>
Cc: Dave Taht <dave.taht@gmail.com>
Cc: Van Jacobson <vanj@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2015-04-30 09:40:40 -07:00 committed by David S. Miller
parent 6c3c1eb3c3
commit a5d2809040
3 changed files with 9 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
include/net/codel.h
View File

@ -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;

2
net/sched/sch_codel.c
View File

@ -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);

2
net/sched/sch_fq_codel.c
View File

@ -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;