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netem: add cell concept to simulate special MAC behavior

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This extension can be used to simulate special link layer
characteristics. Simulate because packet data is not modified, only the
calculation base is changed to delay a packet based on the original
packet size and artificial cell information.

packet_overhead can be used to simulate a link layer header compression
scheme (e.g. set packet_overhead to -20) or with a positive
packet_overhead value an additional MAC header can be simulated. It is
also possible to "replace" the 14 byte Ethernet header with something
else.

cell_size and cell_overhead can be used to simulate link layer schemes,
based on cells, like some TDMA schemes. Another application area are MAC
schemes using a link layer fragmentation with a (small) header each.
Cell size is the maximum amount of data bytes within one cell. Cell
overhead is an additional variable to change the per-cell-overhead
(e.g.  5 byte header per fragment).

Example (5 kbit/s, 20 byte per packet overhead, cell-size 100 byte, per
cell overhead 5 byte):

  tc qdisc add dev eth0 root netem rate 5kbit 20 100 5

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
Signed-off-by: Florian Westphal <fw@strlen.de>
Acked-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Hagen Paul Pfeifer 2011-12-12 14:30:00 +00:00 committed by David S. Miller
parent c7c6575f25
commit 90b41a1cd4
2 changed files with 32 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
include/linux/pkt_sched.h
View File

@ -502,6 +502,9 @@ struct tc_netem_corrupt {
struct tc_netem_rate {
__u32 rate; /* byte/s */
__s32 packet_overhead;
__u32 cell_size;
__s32 cell_overhead;
};
enum {

33
net/sched/sch_netem.c
View File

@ -22,6 +22,7 @@
#include <linux/skbuff.h>
#include <linux/vmalloc.h>
#include <linux/rtnetlink.h>
#include <linux/reciprocal_div.h>
#include <net/netlink.h>
#include <net/pkt_sched.h>
@ -80,6 +81,10 @@ struct netem_sched_data {
u32 reorder;
u32 corrupt;
u32 rate;
s32 packet_overhead;
u32 cell_size;
u32 cell_size_reciprocal;
s32 cell_overhead;
struct crndstate {
u32 last;
@ -299,11 +304,23 @@ static psched_tdiff_t tabledist(psched_tdiff_t mu, psched_tdiff_t sigma,
return x / NETEM_DIST_SCALE + (sigma / NETEM_DIST_SCALE) * t + mu;
}
static psched_time_t packet_len_2_sched_time(unsigned int len, u32 rate)
static psched_time_t packet_len_2_sched_time(unsigned int len, struct netem_sched_data *q)
{
u64 ticks = (u64)len * NSEC_PER_SEC;
u64 ticks;
do_div(ticks, rate);
len += q->packet_overhead;
if (q->cell_size) {
u32 cells = reciprocal_divide(len, q->cell_size_reciprocal);
if (len > cells * q->cell_size) /* extra cell needed for remainder */
cells++;
len = cells * (q->cell_size + q->cell_overhead);
}
ticks = (u64)len * NSEC_PER_SEC;
do_div(ticks, q->rate);
return PSCHED_NS2TICKS(ticks);
}
@ -384,7 +401,7 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch)
if (q->rate) {
struct sk_buff_head *list = &q->qdisc->q;
delay += packet_len_2_sched_time(skb->len, q->rate);
delay += packet_len_2_sched_time(skb->len, q);
if (!skb_queue_empty(list)) {
/*
@ -568,6 +585,11 @@ static void get_rate(struct Qdisc *sch, const struct nlattr *attr)
const struct tc_netem_rate *r = nla_data(attr);
q->rate = r->rate;
q->packet_overhead = r->packet_overhead;
q->cell_size = r->cell_size;
if (q->cell_size)
q->cell_size_reciprocal = reciprocal_value(q->cell_size);
q->cell_overhead = r->cell_overhead;
}
static int get_loss_clg(struct Qdisc *sch, const struct nlattr *attr)
@ -909,6 +931,9 @@ static int netem_dump(struct Qdisc *sch, struct sk_buff *skb)
NLA_PUT(skb, TCA_NETEM_CORRUPT, sizeof(corrupt), &corrupt);
rate.rate = q->rate;
rate.packet_overhead = q->packet_overhead;
rate.cell_size = q->cell_size;
rate.cell_overhead = q->cell_overhead;
NLA_PUT(skb, TCA_NETEM_RATE, sizeof(rate), &rate);
if (dump_loss_model(q, skb) != 0)