1// SPDX-License-Identifier: GPL-2.0-only
  2
  3/* Highlights:
  4 * 1. The major difference between this bpf program and tcp_cubic.c
  5 *    is that this bpf program relies on `cong_control` rather than
  6 *    `cong_avoid` in the struct tcp_congestion_ops.
  7 * 2. Logic such as tcp_cwnd_reduction, tcp_cong_avoid, and
  8 *    tcp_update_pacing_rate is bypassed when `cong_control` is
  9 *    defined, so moving these logic to `cong_control`.
 10 * 3. WARNING: This bpf program is NOT the same as tcp_cubic.c.
 11 *    The main purpose is to show use cases of the arguments in
 12 *    `cong_control`. For simplicity's sake, it reuses tcp cubic's
 13 *    kernel functions.
 14 */
 15
 16#include "bpf_tracing_net.h"
 17#include <bpf/bpf_helpers.h>
 18#include <bpf/bpf_tracing.h>
 19
 20#define USEC_PER_SEC 1000000UL
 21#define TCP_PACING_SS_RATIO (200)
 22#define TCP_PACING_CA_RATIO (120)
 23#define TCP_REORDERING (12)
 24
 25#define min(a, b) ((a) < (b) ? (a) : (b))
 26#define max(a, b) ((a) > (b) ? (a) : (b))
 27#define after(seq2, seq1) before(seq1, seq2)
 28
 29extern void cubictcp_init(struct sock *sk) __ksym;
 30extern void cubictcp_cwnd_event(struct sock *sk, enum tcp_ca_event event) __ksym;
 31extern __u32 cubictcp_recalc_ssthresh(struct sock *sk) __ksym;
 32extern void cubictcp_state(struct sock *sk, __u8 new_state) __ksym;
 33extern __u32 tcp_reno_undo_cwnd(struct sock *sk) __ksym;
 34extern void cubictcp_acked(struct sock *sk, const struct ack_sample *sample) __ksym;
 35extern void cubictcp_cong_avoid(struct sock *sk, __u32 ack, __u32 acked) __ksym;
 36
 37static bool before(__u32 seq1, __u32 seq2)
 38{
 39	return (__s32)(seq1-seq2) < 0;
 40}
 41
 42static __u64 div64_u64(__u64 dividend, __u64 divisor)
 43{
 44	return dividend / divisor;
 45}
 46
 47static void tcp_update_pacing_rate(struct sock *sk)
 48{
 49	const struct tcp_sock *tp = tcp_sk(sk);
 50	__u64 rate;
 51
 52	/* set sk_pacing_rate to 200 % of current rate (mss * cwnd / srtt) */
 53	rate = (__u64)tp->mss_cache * ((USEC_PER_SEC / 100) << 3);
 54
 55	/* current rate is (cwnd * mss) / srtt
 56	 * In Slow Start [1], set sk_pacing_rate to 200 % the current rate.
 57	 * In Congestion Avoidance phase, set it to 120 % the current rate.
 58	 *
 59	 * [1] : Normal Slow Start condition is (tp->snd_cwnd < tp->snd_ssthresh)
 60	 *	 If snd_cwnd >= (tp->snd_ssthresh / 2), we are approaching
 61	 *	 end of slow start and should slow down.
 62	 */
 63	if (tp->snd_cwnd < tp->snd_ssthresh / 2)
 64		rate *= TCP_PACING_SS_RATIO;
 65	else
 66		rate *= TCP_PACING_CA_RATIO;
 67
 68	rate *= max(tp->snd_cwnd, tp->packets_out);
 69
 70	if (tp->srtt_us)
 71		rate = div64_u64(rate, (__u64)tp->srtt_us);
 72
 73	sk->sk_pacing_rate = min(rate, sk->sk_max_pacing_rate);
 74}
 75
 76static void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked,
 77			       int newly_lost, int flag)
 78{
 79	struct tcp_sock *tp = tcp_sk(sk);
 80	int sndcnt = 0;
 81	__u32 pkts_in_flight = tp->packets_out - (tp->sacked_out + tp->lost_out) + tp->retrans_out;
 82	int delta = tp->snd_ssthresh - pkts_in_flight;
 83
 84	if (newly_acked_sacked <= 0 || !tp->prior_cwnd)
 85		return;
 86
 87	__u32 prr_delivered = tp->prr_delivered + newly_acked_sacked;
 88
 89	if (delta < 0) {
 90		__u64 dividend =
 91			(__u64)tp->snd_ssthresh * prr_delivered + tp->prior_cwnd - 1;
 92		sndcnt = (__u32)div64_u64(dividend, (__u64)tp->prior_cwnd) - tp->prr_out;
 93	} else {
 94		sndcnt = max(prr_delivered - tp->prr_out, newly_acked_sacked);
 95		if (flag & FLAG_SND_UNA_ADVANCED && !newly_lost)
 96			sndcnt++;
 97		sndcnt = min(delta, sndcnt);
 98	}
 99	/* Force a fast retransmit upon entering fast recovery */
100	sndcnt = max(sndcnt, (tp->prr_out ? 0 : 1));
101	tp->snd_cwnd = pkts_in_flight + sndcnt;
102}
103
104/* Decide wheather to run the increase function of congestion control. */
105static bool tcp_may_raise_cwnd(const struct sock *sk, const int flag)
106{
107	if (tcp_sk(sk)->reordering > TCP_REORDERING)
108		return flag & FLAG_FORWARD_PROGRESS;
109
110	return flag & FLAG_DATA_ACKED;
111}
112
113SEC("struct_ops")
114void BPF_PROG(bpf_cubic_init, struct sock *sk)
115{
116	cubictcp_init(sk);
117}
118
119SEC("struct_ops")
120void BPF_PROG(bpf_cubic_cwnd_event, struct sock *sk, enum tcp_ca_event event)
121{
122	cubictcp_cwnd_event(sk, event);
123}
124
125SEC("struct_ops")
126void BPF_PROG(bpf_cubic_cong_control, struct sock *sk, __u32 ack, int flag,
127	      const struct rate_sample *rs)
128{
129	struct tcp_sock *tp = tcp_sk(sk);
130
131	if (((1<<TCP_CA_CWR) | (1<<TCP_CA_Recovery)) &
132			(1 << inet_csk(sk)->icsk_ca_state)) {
133		/* Reduce cwnd if state mandates */
134		tcp_cwnd_reduction(sk, rs->acked_sacked, rs->losses, flag);
135
136		if (!before(tp->snd_una, tp->high_seq)) {
137			/* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
138			if (tp->snd_ssthresh < TCP_INFINITE_SSTHRESH &&
139					inet_csk(sk)->icsk_ca_state == TCP_CA_CWR) {
140				tp->snd_cwnd = tp->snd_ssthresh;
141				tp->snd_cwnd_stamp = tcp_jiffies32;
142			}
143		}
144	} else if (tcp_may_raise_cwnd(sk, flag)) {
145		/* Advance cwnd if state allows */
146		cubictcp_cong_avoid(sk, ack, rs->acked_sacked);
147		tp->snd_cwnd_stamp = tcp_jiffies32;
148	}
149
150	tcp_update_pacing_rate(sk);
151}
152
153SEC("struct_ops")
154__u32 BPF_PROG(bpf_cubic_recalc_ssthresh, struct sock *sk)
155{
156	return cubictcp_recalc_ssthresh(sk);
157}
158
159SEC("struct_ops")
160void BPF_PROG(bpf_cubic_state, struct sock *sk, __u8 new_state)
161{
162	cubictcp_state(sk, new_state);
163}
164
165SEC("struct_ops")
166void BPF_PROG(bpf_cubic_acked, struct sock *sk, const struct ack_sample *sample)
167{
168	cubictcp_acked(sk, sample);
169}
170
171SEC("struct_ops")
172__u32 BPF_PROG(bpf_cubic_undo_cwnd, struct sock *sk)
173{
174	return tcp_reno_undo_cwnd(sk);
175}
176
177SEC(".struct_ops")
178struct tcp_congestion_ops cc_cubic = {
179	.init		= (void *)bpf_cubic_init,
180	.ssthresh	= (void *)bpf_cubic_recalc_ssthresh,
181	.cong_control	= (void *)bpf_cubic_cong_control,
182	.set_state	= (void *)bpf_cubic_state,
183	.undo_cwnd	= (void *)bpf_cubic_undo_cwnd,
184	.cwnd_event	= (void *)bpf_cubic_cwnd_event,
185	.pkts_acked     = (void *)bpf_cubic_acked,
186	.name		= "bpf_cc_cubic",
187};
188
189char _license[] SEC("license") = "GPL";