// SPDX-License-Identifier: GPL-2.0-only
/* Highlights:
* 1. The major difference between this bpf program and tcp_cubic.c
* is that this bpf program relies on `cong_control` rather than
* `cong_avoid` in the struct tcp_congestion_ops.
* 2. Logic such as tcp_cwnd_reduction, tcp_cong_avoid, and
* tcp_update_pacing_rate is bypassed when `cong_control` is
* defined, so moving these logic to `cong_control`.
* 3. WARNING: This bpf program is NOT the same as tcp_cubic.c.
* The main purpose is to show use cases of the arguments in
* `cong_control`. For simplicity's sake, it reuses tcp cubic's
* kernel functions.
*/
#include "bpf_tracing_net.h"
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>
#define USEC_PER_SEC 1000000UL
#define TCP_PACING_SS_RATIO (200)
#define TCP_PACING_CA_RATIO (120)
#define TCP_REORDERING (12)
#define min(a, b) ((a) < (b) ? (a) : (b))
#define max(a, b) ((a) > (b) ? (a) : (b))
#define after(seq2, seq1) before(seq1, seq2)
extern void cubictcp_init(struct sock *sk) __ksym;
extern void cubictcp_cwnd_event(struct sock *sk, enum tcp_ca_event event) __ksym;
extern __u32 cubictcp_recalc_ssthresh(struct sock *sk) __ksym;
extern void cubictcp_state(struct sock *sk, __u8 new_state) __ksym;
extern __u32 tcp_reno_undo_cwnd(struct sock *sk) __ksym;
extern void cubictcp_acked(struct sock *sk, const struct ack_sample *sample) __ksym;
extern void cubictcp_cong_avoid(struct sock *sk, __u32 ack, __u32 acked) __ksym;
static bool before(__u32 seq1, __u32 seq2)
{
return (__s32)(seq1-seq2) < 0;
}
static __u64 div64_u64(__u64 dividend, __u64 divisor)
{
return dividend / divisor;
}
static void tcp_update_pacing_rate(struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
__u64 rate;
/* set sk_pacing_rate to 200 % of current rate (mss * cwnd / srtt) */
rate = (__u64)tp->mss_cache * ((USEC_PER_SEC / 100) << 3);
/* current rate is (cwnd * mss) / srtt
* In Slow Start [1], set sk_pacing_rate to 200 % the current rate.
* In Congestion Avoidance phase, set it to 120 % the current rate.
*
* [1] : Normal Slow Start condition is (tp->snd_cwnd < tp->snd_ssthresh)
* If snd_cwnd >= (tp->snd_ssthresh / 2), we are approaching
* end of slow start and should slow down.
*/
if (tp->snd_cwnd < tp->snd_ssthresh / 2)
rate *= TCP_PACING_SS_RATIO;
else
rate *= TCP_PACING_CA_RATIO;
rate *= max(tp->snd_cwnd, tp->packets_out);
if (tp->srtt_us)
rate = div64_u64(rate, (__u64)tp->srtt_us);
sk->sk_pacing_rate = min(rate, sk->sk_max_pacing_rate);
}
static void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked,
int newly_lost, int flag)
{
struct tcp_sock *tp = tcp_sk(sk);
int sndcnt = 0;
__u32 pkts_in_flight = tp->packets_out - (tp->sacked_out + tp->lost_out) + tp->retrans_out;
int delta = tp->snd_ssthresh - pkts_in_flight;
if (newly_acked_sacked <= 0 || !tp->prior_cwnd)
return;
__u32 prr_delivered = tp->prr_delivered + newly_acked_sacked;
if (delta < 0) {
__u64 dividend =
(__u64)tp->snd_ssthresh * prr_delivered + tp->prior_cwnd - 1;
sndcnt = (__u32)div64_u64(dividend, (__u64)tp->prior_cwnd) - tp->prr_out;
} else {
sndcnt = max(prr_delivered - tp->prr_out, newly_acked_sacked);
if (flag & FLAG_SND_UNA_ADVANCED && !newly_lost)
sndcnt++;
sndcnt = min(delta, sndcnt);
}
/* Force a fast retransmit upon entering fast recovery */
sndcnt = max(sndcnt, (tp->prr_out ? 0 : 1));
tp->snd_cwnd = pkts_in_flight + sndcnt;
}
/* Decide wheather to run the increase function of congestion control. */
static bool tcp_may_raise_cwnd(const struct sock *sk, const int flag)
{
if (tcp_sk(sk)->reordering > TCP_REORDERING)
return flag & FLAG_FORWARD_PROGRESS;
return flag & FLAG_DATA_ACKED;
}
SEC("struct_ops")
void BPF_PROG(bpf_cubic_init, struct sock *sk)
{
cubictcp_init(sk);
}
SEC("struct_ops")
void BPF_PROG(bpf_cubic_cwnd_event, struct sock *sk, enum tcp_ca_event event)
{
cubictcp_cwnd_event(sk, event);
}
SEC("struct_ops")
void BPF_PROG(bpf_cubic_cong_control, struct sock *sk, __u32 ack, int flag,
const struct rate_sample *rs)
{
struct tcp_sock *tp = tcp_sk(sk);
if (((1<<TCP_CA_CWR) | (1<<TCP_CA_Recovery)) &
(1 << inet_csk(sk)->icsk_ca_state)) {
/* Reduce cwnd if state mandates */
tcp_cwnd_reduction(sk, rs->acked_sacked, rs->losses, flag);
if (!before(tp->snd_una, tp->high_seq)) {
/* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
if (tp->snd_ssthresh < TCP_INFINITE_SSTHRESH &&
inet_csk(sk)->icsk_ca_state == TCP_CA_CWR) {
tp->snd_cwnd = tp->snd_ssthresh;
tp->snd_cwnd_stamp = tcp_jiffies32;
}
}
} else if (tcp_may_raise_cwnd(sk, flag)) {
/* Advance cwnd if state allows */
cubictcp_cong_avoid(sk, ack, rs->acked_sacked);
tp->snd_cwnd_stamp = tcp_jiffies32;
}
tcp_update_pacing_rate(sk);
}
SEC("struct_ops")
__u32 BPF_PROG(bpf_cubic_recalc_ssthresh, struct sock *sk)
{
return cubictcp_recalc_ssthresh(sk);
}
SEC("struct_ops")
void BPF_PROG(bpf_cubic_state, struct sock *sk, __u8 new_state)
{
cubictcp_state(sk, new_state);
}
SEC("struct_ops")
void BPF_PROG(bpf_cubic_acked, struct sock *sk, const struct ack_sample *sample)
{
cubictcp_acked(sk, sample);
}
SEC("struct_ops")
__u32 BPF_PROG(bpf_cubic_undo_cwnd, struct sock *sk)
{
return tcp_reno_undo_cwnd(sk);
}
SEC(".struct_ops")
struct tcp_congestion_ops cc_cubic = {
.init = (void *)bpf_cubic_init,
.ssthresh = (void *)bpf_cubic_recalc_ssthresh,
.cong_control = (void *)bpf_cubic_cong_control,
.set_state = (void *)bpf_cubic_state,
.undo_cwnd = (void *)bpf_cubic_undo_cwnd,
.cwnd_event = (void *)bpf_cubic_cwnd_event,
.pkts_acked = (void *)bpf_cubic_acked,
.name = "bpf_cc_cubic",
};
char _license[] SEC("license") = "GPL";
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