tools/testing/selftests/bpf/progs/bpf_dctcp.c

Source file repositories/reference/linux-study-clean/tools/testing/selftests/bpf/progs/bpf_dctcp.c

File Facts

System
Linux kernel
Corpus path
tools/testing/selftests/bpf/progs/bpf_dctcp.c
Extension
.c
Size
6739 bytes
Lines
259
Domain
Support Tooling And Documentation
Bucket
tools
Inferred role
Support Tooling And Documentation: implementation source
Status
source implementation candidate

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

Dependency Surface

Detected Declarations

Annotated Snippet

struct bpf_dctcp {
	__u32 old_delivered;
	__u32 old_delivered_ce;
	__u32 prior_rcv_nxt;
	__u32 dctcp_alpha;
	__u32 next_seq;
	__u32 ce_state;
	__u32 loss_cwnd;
};

static unsigned int dctcp_shift_g = 4; /* g = 1/2^4 */
static unsigned int dctcp_alpha_on_init = DCTCP_MAX_ALPHA;

static void dctcp_reset(const struct tcp_sock *tp, struct bpf_dctcp *ca)
{
	ca->next_seq = tp->snd_nxt;

	ca->old_delivered = tp->delivered;
	ca->old_delivered_ce = tp->delivered_ce;
}

SEC("struct_ops")
void BPF_PROG(bpf_dctcp_init, struct sock *sk)
{
	const struct tcp_sock *tp = tcp_sk(sk);
	struct bpf_dctcp *ca = inet_csk_ca(sk);
	int *stg;

	if (!(tp->ecn_flags & TCP_ECN_OK) && fallback_cc[0]) {
		/* Switch to fallback */
		if (bpf_setsockopt(sk, SOL_TCP, TCP_CONGESTION,
				   (void *)fallback_cc, sizeof(fallback_cc)) == -EBUSY)
			ebusy_cnt++;

		/* Switch back to myself and the recurred bpf_dctcp_init()
		 * will get -EBUSY for all bpf_setsockopt(TCP_CONGESTION),
		 * except the last "cdg" one.
		 */
		if (bpf_setsockopt(sk, SOL_TCP, TCP_CONGESTION,
				   (void *)bpf_dctcp, sizeof(bpf_dctcp)) == -EBUSY)
			ebusy_cnt++;

		/* Switch back to fallback */
		if (bpf_setsockopt(sk, SOL_TCP, TCP_CONGESTION,
				   (void *)fallback_cc, sizeof(fallback_cc)) == -EBUSY)
			ebusy_cnt++;

		/* Expecting -ENOTSUPP for tcp_cdg_res */
		tcp_cdg_res = bpf_setsockopt(sk, SOL_TCP, TCP_CONGESTION,
					     (void *)tcp_cdg, sizeof(tcp_cdg));
		bpf_getsockopt(sk, SOL_TCP, TCP_CONGESTION,
			       (void *)cc_res, sizeof(cc_res));
		return;
	}

	ca->prior_rcv_nxt = tp->rcv_nxt;
	ca->dctcp_alpha = min(dctcp_alpha_on_init, DCTCP_MAX_ALPHA);
	ca->loss_cwnd = 0;
	ca->ce_state = 0;

	stg = bpf_sk_storage_get(&sk_stg_map, (void *)tp, NULL, 0);
	if (stg) {
		stg_result = *stg;
		bpf_sk_storage_delete(&sk_stg_map, (void *)tp);
	}
	dctcp_reset(tp, ca);
}

SEC("struct_ops")
__u32 BPF_PROG(bpf_dctcp_ssthresh, struct sock *sk)
{
	struct bpf_dctcp *ca = inet_csk_ca(sk);
	struct tcp_sock *tp = tcp_sk(sk);

	ca->loss_cwnd = tp->snd_cwnd;
	return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->dctcp_alpha) >> 11U), 2U);
}

SEC("struct_ops")
void BPF_PROG(bpf_dctcp_update_alpha, struct sock *sk, __u32 flags)
{
	const struct tcp_sock *tp = tcp_sk(sk);
	struct bpf_dctcp *ca = inet_csk_ca(sk);

	/* Expired RTT */
	if (!before(tp->snd_una, ca->next_seq)) {
		__u32 delivered_ce = tp->delivered_ce - ca->old_delivered_ce;
		__u32 alpha = ca->dctcp_alpha;

		/* alpha = (1 - g) * alpha + g * F */

Annotation

Implementation Notes