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56af5e749f
Currently, when doing rate limiting using the tc-police(8) action, the
easiest way is to simply drop the packets which exceed or conform the
configured bandwidth limit. Add a new option to tc-skbmod(8), so that
users may use the ECN [1] extension to explicitly inform the receiver
about the congestion instead of dropping packets "on the floor".
The 2 least significant bits of the Traffic Class field in IPv4 and IPv6
headers are used to represent different ECN states [2]:
0b00: "Non ECN-Capable Transport", Non-ECT
0b10: "ECN Capable Transport", ECT(0)
0b01: "ECN Capable Transport", ECT(1)
0b11: "Congestion Encountered", CE
As an example:
$ tc filter add dev eth0 parent 1: protocol ip prio 10 \
matchall action skbmod ecn
Doing the above marks all ECT(0) and ECT(1) packets as CE. It does NOT
affect Non-ECT or non-IP packets. In the tc-police scenario mentioned
above, users may pipe a tc-police action and a tc-skbmod "ecn" action
together to achieve ECN-based rate limiting.
For TCP connections, upon receiving a CE packet, the receiver will respond
with an ECE packet, asking the sender to reduce their congestion window.
However ECN also works with other L4 protocols e.g. DCCP and SCTP [2], and
our implementation does not touch or care about L4 headers.
The updated tc-skbmod SYNOPSIS looks like the following:
tc ... action skbmod { set SETTABLE | swap SWAPPABLE | ecn } ...
Only one of "set", "swap" or "ecn" shall be used in a single tc-skbmod
command. Trying to use more than one of them at a time is considered
undefined behavior; pipe multiple tc-skbmod commands together instead.
"set" and "swap" only affect Ethernet packets, while "ecn" only affects
IPv{4,6} packets.
It is also worth mentioning that, in theory, the same effect could be
achieved by piping a "police" action and a "bpf" action using the
bpf_skb_ecn_set_ce() helper, but this requires eBPF programming from the
user, thus impractical.
Depends on patch "net/sched: act_skbmod: Skip non-Ethernet packets".
[1] https://datatracker.ietf.org/doc/html/rfc3168
[2] https://en.wikipedia.org/wiki/Explicit_Congestion_Notification
Reviewed-by: Cong Wang <cong.wang@bytedance.com>
Signed-off-by: Peilin Ye <peilin.ye@bytedance.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
39 lines
841 B
C
39 lines
841 B
C
/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
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/*
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* Copyright (c) 2016, Jamal Hadi Salim
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*/
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#ifndef __LINUX_TC_SKBMOD_H
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#define __LINUX_TC_SKBMOD_H
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#include <linux/pkt_cls.h>
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#define SKBMOD_F_DMAC 0x1
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#define SKBMOD_F_SMAC 0x2
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#define SKBMOD_F_ETYPE 0x4
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#define SKBMOD_F_SWAPMAC 0x8
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#define SKBMOD_F_ECN 0x10
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struct tc_skbmod {
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tc_gen;
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__u64 flags;
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};
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enum {
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TCA_SKBMOD_UNSPEC,
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TCA_SKBMOD_TM,
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TCA_SKBMOD_PARMS,
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TCA_SKBMOD_DMAC,
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TCA_SKBMOD_SMAC,
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TCA_SKBMOD_ETYPE,
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TCA_SKBMOD_PAD,
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__TCA_SKBMOD_MAX
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};
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#define TCA_SKBMOD_MAX (__TCA_SKBMOD_MAX - 1)
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#endif
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