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![brakmo](/assets/img/avatar_default.png)
Adds more stats to HBM, including average cwnd and rtt of all TCP flows, percents of packets that are ecn ce marked and distribution of return values. Signed-off-by: Lawrence Brakmo <brakmo@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
179 lines
5.5 KiB
C
179 lines
5.5 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/* Copyright (c) 2019 Facebook
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of version 2 of the GNU General Public
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* License as published by the Free Software Foundation.
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*
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* Sample Host Bandwidth Manager (HBM) BPF program.
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*
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* A cgroup skb BPF egress program to limit cgroup output bandwidth.
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* It uses a modified virtual token bucket queue to limit average
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* egress bandwidth. The implementation uses credits instead of tokens.
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* Negative credits imply that queueing would have happened (this is
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* a virtual queue, so no queueing is done by it. However, queueing may
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* occur at the actual qdisc (which is not used for rate limiting).
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*
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* This implementation uses 3 thresholds, one to start marking packets and
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* the other two to drop packets:
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* CREDIT
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* - <--------------------------|------------------------> +
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* | | | 0
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* | Large pkt |
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* | drop thresh |
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* Small pkt drop Mark threshold
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* thresh
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*
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* The effect of marking depends on the type of packet:
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* a) If the packet is ECN enabled and it is a TCP packet, then the packet
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* is ECN marked.
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* b) If the packet is a TCP packet, then we probabilistically call tcp_cwr
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* to reduce the congestion window. The current implementation uses a linear
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* distribution (0% probability at marking threshold, 100% probability
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* at drop threshold).
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* c) If the packet is not a TCP packet, then it is dropped.
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*
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* If the credit is below the drop threshold, the packet is dropped. If it
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* is a TCP packet, then it also calls tcp_cwr since packets dropped by
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* by a cgroup skb BPF program do not automatically trigger a call to
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* tcp_cwr in the current kernel code.
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*
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* This BPF program actually uses 2 drop thresholds, one threshold
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* for larger packets (>= 120 bytes) and another for smaller packets. This
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* protects smaller packets such as SYNs, ACKs, etc.
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*
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* The default bandwidth limit is set at 1Gbps but this can be changed by
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* a user program through a shared BPF map. In addition, by default this BPF
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* program does not limit connections using loopback. This behavior can be
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* overwritten by the user program. There is also an option to calculate
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* some statistics, such as percent of packets marked or dropped, which
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* the user program can access.
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*
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* A latter patch provides such a program (hbm.c)
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*/
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#include "hbm_kern.h"
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SEC("cgroup_skb/egress")
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int _hbm_out_cg(struct __sk_buff *skb)
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{
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struct hbm_pkt_info pkti;
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int len = skb->len;
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unsigned int queue_index = 0;
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unsigned long long curtime;
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int credit;
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signed long long delta = 0, new_credit;
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int max_credit = MAX_CREDIT;
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bool congestion_flag = false;
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bool drop_flag = false;
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bool cwr_flag = false;
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bool ecn_ce_flag = false;
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struct hbm_vqueue *qdp;
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struct hbm_queue_stats *qsp = NULL;
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int rv = ALLOW_PKT;
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qsp = bpf_map_lookup_elem(&queue_stats, &queue_index);
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if (qsp != NULL && !qsp->loopback && (skb->ifindex == 1))
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return ALLOW_PKT;
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hbm_get_pkt_info(skb, &pkti);
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// We may want to account for the length of headers in len
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// calculation, like ETH header + overhead, specially if it
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// is a gso packet. But I am not doing it right now.
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qdp = bpf_get_local_storage(&queue_state, 0);
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if (!qdp)
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return ALLOW_PKT;
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else if (qdp->lasttime == 0)
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hbm_init_vqueue(qdp, 1024);
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curtime = bpf_ktime_get_ns();
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// Begin critical section
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bpf_spin_lock(&qdp->lock);
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credit = qdp->credit;
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delta = curtime - qdp->lasttime;
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/* delta < 0 implies that another process with a curtime greater
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* than ours beat us to the critical section and already added
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* the new credit, so we should not add it ourselves
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*/
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if (delta > 0) {
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qdp->lasttime = curtime;
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new_credit = credit + CREDIT_PER_NS(delta, qdp->rate);
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if (new_credit > MAX_CREDIT)
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credit = MAX_CREDIT;
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else
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credit = new_credit;
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}
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credit -= len;
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qdp->credit = credit;
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bpf_spin_unlock(&qdp->lock);
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// End critical section
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// Check if we should update rate
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if (qsp != NULL && (qsp->rate * 128) != qdp->rate) {
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qdp->rate = qsp->rate * 128;
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bpf_printk("Updating rate: %d (1sec:%llu bits)\n",
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(int)qdp->rate,
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CREDIT_PER_NS(1000000000, qdp->rate) * 8);
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}
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// Set flags (drop, congestion, cwr)
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// Dropping => we are congested, so ignore congestion flag
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if (credit < -DROP_THRESH ||
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(len > LARGE_PKT_THRESH && credit < -LARGE_PKT_DROP_THRESH)) {
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// Very congested, set drop packet
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drop_flag = true;
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if (pkti.ecn)
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congestion_flag = true;
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else if (pkti.is_tcp)
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cwr_flag = true;
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} else if (credit < 0) {
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// Congested, set congestion flag
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if (pkti.ecn || pkti.is_tcp) {
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if (credit < -MARK_THRESH)
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congestion_flag = true;
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else
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congestion_flag = false;
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} else {
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congestion_flag = true;
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}
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}
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if (congestion_flag) {
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if (bpf_skb_ecn_set_ce(skb)) {
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ecn_ce_flag = true;
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} else {
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if (pkti.is_tcp) {
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unsigned int rand = bpf_get_prandom_u32();
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if (-credit >= MARK_THRESH +
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(rand % MARK_REGION_SIZE)) {
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// Do congestion control
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cwr_flag = true;
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}
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} else if (len > LARGE_PKT_THRESH) {
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// Problem if too many small packets?
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drop_flag = true;
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}
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}
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}
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if (qsp != NULL)
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if (qsp->no_cn)
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cwr_flag = false;
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hbm_update_stats(qsp, len, curtime, congestion_flag, drop_flag,
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cwr_flag, ecn_ce_flag, &pkti, credit);
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if (drop_flag) {
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__sync_add_and_fetch(&(qdp->credit), len);
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rv = DROP_PKT;
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}
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if (cwr_flag)
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rv |= 2;
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return rv;
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}
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char _license[] SEC("license") = "GPL";
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