[474] in linux-net channel archive
Re: [Project] Managing Available Bandwidth
daemon@ATHENA.MIT.EDU (Matthias Urlichs)
Tue Jun 13 14:32:42 1995
To: submit-linux-dev-net@ratatosk.yggdrasil.com
From: urlichs@smurf.noris.de (Matthias Urlichs)
Date: 13 Jun 1995 18:29:01 +0200
Some comments:
(a) Busy waiting is extremely antisocial. Don't even think about doing it
that way.
(b) Don't drop packets received from the bandwidth-reduced line; delay
(and possibly drop) outgoing stuff only. Throttling the data rate on
the other end is the job of the other side.
(c) Look at drivers/net/eql.c in the 1.3.0 kernel. It may provide a
starting point.
(d) Looking at the aforementioned file myself..: PLEASE, everybody, check
whether you get NULL from kmalloc!
The basic processing should probably look somewhat like this:
- Assume two variables: bw_lim is the number of bytes to send, bw_now says
how many bytes you did send. Both are per 10th of a second or so.
- Every 10/th second do this:
if(bw_now > bw_lim)
bw_now -= bw_lim;
else
bw_now = 0;
while(bw_now < bw_lim) {
dequeue_packet();
if(packet == NULL) break;
bw_now += packet_length();
send_it();
}
- If you get a packet:
if(packet_in_queue()) {
if(queue_full()) {
send_ICMP_sourcequench(); /* at most once per second or so */
drop_packet();
else
enqueue_packet();
} else if(bw_now >= bw_lim) {
enqueue_packet();
} else {
bw_now += packet_length();
send_packet();
}
Quite simple really. The problem is how to figure out which bw_now / bw_lim
variables to use. Ideally, you'd have a priority scheme (Telnet first, then
WWW; FTP and Netnews may soak up the remaining bandwidth), associate one
or possibly many IP filter records with each priority, and share bw_now
among them (Telnet and WWW together may not soak up more than XXX kB/sec).
Next problem: Fairness. If you're not careful, a strict priority scheme
will cause your low-priority sessions to starve themselves to death -- the
policies built into TCP might do that even if the bandwidth distribution
mechanism tries to distribute the bandwidth.
--
Four things belong to a judge: to hear courteously, to answer wisely,
to consider soberly, and to decide impartially.
-- Socrates
--
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