Slotting is a crude approximation of the behaviors of shared media such
as cable, wifi, and LTE, which gather up a bunch of packets within a
varying delay window and deliver them, relative to that, nearly all at
once.
It works within the existing loss, duplication, jitter and delay
parameters of netem. Some amount of inherent latency must be specified,
regardless.
The new "slot" parameter specifies a minimum and maximum delay between
transmission attempts.
The "bytes" and "packets" parameters can be used to limit the amount of
information transferred per slot.
Examples of use:
tc qdisc add dev eth0 root netem delay 200us \
slot 800us 10ms bytes 64k packets 42
A more correct example, using stacked netem instances and a packet limit
to emulate a tail drop wifi queue with slots and variable packet
delivery, with a 200Mbit isochronous underlying rate, and 20ms path
delay:
tc qdisc add dev eth0 root handle 1: netem delay 20ms rate 200mbit \
limit 10000
tc qdisc add dev eth0 parent 1:1 handle 10:1 netem delay 200us \
slot 800us 10ms bytes 64k packets 42 limit 512
Signed-off-by: Yousuk Seung <ysseung@google.com>
Signed-off-by: Dave Taht <dave.taht@gmail.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David Ahern <dsahern@gmail.com>
As the kernel code says, limit is actually the amount of packets it can
hold queued at a time, as per:
static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
struct sk_buff **to_free)
{
...
if (unlikely(sch->q.qlen >= sch->limit))
return qdisc_drop_all(skb, sch, to_free);
So lets fix the description of the field in the man page.
Signed-off-by: Marcelo Ricardo Leitner <mleitner@redhat.com>
Signed-off-by: David Ahern <dsahern@gmail.com>
This patch updates the netem manpage to describe how to use
netem to mark packets with ecn instead of dropping them.
Signed-off-by: Vijay Subramanian <subramanian.vijay@gmail.com>
The syntax used in the example on reordering in the manpage is inconsistent with
the usage syntax. Moreover, the text does not describe the reordering process
in the kernel correctly. This patch fixes these two issues.
Signed-off-by: Vijay Subramanian <subramanian.vijay@gmail.com>
