bpf: tcp: Add bpf_cubic example (6de4a9c4) · Commits · 戴 / test

tools/testing/selftests/bpf/bpf_tcp_helpers.h

+16 −0

Original line number	Diff line number	Diff line
		@@ -6,13 +6,28 @@
		#include <linux/types.h>
		#include <bpf/bpf_helpers.h>
		#include <bpf/bpf_core_read.h>
		#include "bpf_trace_helpers.h"

		#define BPF_STRUCT_OPS(name, args...) \
		SEC("struct_ops/"#name) \
		BPF_PROG(name, args)

		#define tcp_jiffies32 ((__u32)bpf_jiffies64())

		struct sock_common {
		unsigned char skc_state;
		} __attribute__((preserve_access_index));

		enum sk_pacing {
		SK_PACING_NONE = 0,
		SK_PACING_NEEDED = 1,
		SK_PACING_FQ = 2,
		};

		struct sock {
		struct sock_common __sk_common;
		unsigned long sk_pacing_rate;
		__u32 sk_pacing_status; /* see enum sk_pacing */
		} __attribute__((preserve_access_index));

		struct inet_sock {
		@@ -54,6 +69,7 @@ struct tcp_sock {
		__u32 max_packets_out;
		__u32 lsndtime;
		__u32 prior_cwnd;
		__u64 tcp_mstamp; /* most recent packet received/sent */
		} __attribute__((preserve_access_index));

		static __always_inline struct inet_connection_sock inet_csk(const struct sock sk)

tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c

+25 −0

Original line number	Diff line number	Diff line
		@@ -4,6 +4,7 @@
		#include <linux/err.h>
		#include <test_progs.h>
		#include "bpf_dctcp.skel.h"
		#include "bpf_cubic.skel.h"

		#define min(a, b) ((a) < (b) ? (a) : (b))

		@@ -158,6 +159,28 @@ done:
		close(fd);
		}

		static void test_cubic(void)
		{
		struct bpf_cubic *cubic_skel;
		struct bpf_link *link;

		cubic_skel = bpf_cubic__open_and_load();
		if (CHECK(!cubic_skel, "bpf_cubic__open_and_load", "failed\n"))
		return;

		link = bpf_map__attach_struct_ops(cubic_skel->maps.cubic);
		if (CHECK(IS_ERR(link), "bpf_map__attach_struct_ops", "err:%ld\n",
		PTR_ERR(link))) {
		bpf_cubic__destroy(cubic_skel);
		return;
		}

		do_test("bpf_cubic");

		bpf_link__destroy(link);
		bpf_cubic__destroy(cubic_skel);
		}

		static void test_dctcp(void)
		{
		struct bpf_dctcp *dctcp_skel;
		@@ -184,4 +207,6 @@ void test_bpf_tcp_ca(void)
		{
		if (test__start_subtest("dctcp"))
		test_dctcp();
		if (test__start_subtest("cubic"))
		test_cubic();
		}

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

0 → 100644

+544 −0

Original line number	Diff line number	Diff line
		// SPDX-License-Identifier: GPL-2.0-only

		/* WARNING: This implemenation is not necessarily the same
		* as the tcp_cubic.c. The purpose is mainly for testing
		* the kernel BPF logic.
		*
		* Highlights:
		* 1. CONFIG_HZ .kconfig map is used.
		* 2. In bictcp_update(), calculation is changed to use usec
		* resolution (i.e. USEC_PER_JIFFY) instead of using jiffies.
		* Thus, usecs_to_jiffies() is not used in the bpf_cubic.c.
		* 3. In bitctcp_update() [under tcp_friendliness], the original
		* "while (ca->ack_cnt > delta)" loop is changed to the equivalent
		* "ca->ack_cnt / delta" operation.
		*/

		#include <linux/bpf.h>
		#include "bpf_tcp_helpers.h"

		char _license[] SEC("license") = "GPL";

		#define clamp(val, lo, hi) min((typeof(val))max(val, lo), hi)

		#define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation
		* max_cwnd = snd_cwnd * beta
		*/
		#define BICTCP_HZ 10 /* BIC HZ 2^10 = 1024 */

		/* Two methods of hybrid slow start */
		#define HYSTART_ACK_TRAIN 0x1
		#define HYSTART_DELAY 0x2

		/* Number of delay samples for detecting the increase of delay */
		#define HYSTART_MIN_SAMPLES 8
		#define HYSTART_DELAY_MIN (4000U) /* 4ms */
		#define HYSTART_DELAY_MAX (16000U) /* 16 ms */
		#define HYSTART_DELAY_THRESH(x) clamp(x, HYSTART_DELAY_MIN, HYSTART_DELAY_MAX)

		static int fast_convergence = 1;
		static const int beta = 717; /* = 717/1024 (BICTCP_BETA_SCALE) */
		static int initial_ssthresh;
		static const int bic_scale = 41;
		static int tcp_friendliness = 1;

		static int hystart = 1;
		static int hystart_detect = HYSTART_ACK_TRAIN \| HYSTART_DELAY;
		static int hystart_low_window = 16;
		static int hystart_ack_delta_us = 2000;

		static const __u32 cube_rtt_scale = (bic_scale * 10); /* 1024c/rtt /
		static const __u32 beta_scale = 8*(BICTCP_BETA_SCALE+beta) / 3
		/ (BICTCP_BETA_SCALE - beta);
		/* calculate the "K" for (wmax-cwnd) = c/rtt * K^3
		* so K = cubic_root( (wmax-cwnd)*rtt/c )
		* the unit of K is bictcp_HZ=2^10, not HZ
		*
		* c = bic_scale >> 10
		* rtt = 100ms
		*
		* the following code has been designed and tested for
		* cwnd < 1 million packets
		* RTT < 100 seconds
		* HZ < 1,000,00 (corresponding to 10 nano-second)
		*/

		/* 1/c * 2^2bictcp_HZ srtt, 2^40 */
		static const __u64 cube_factor = (__u64)(1ull << (10+3*BICTCP_HZ))
		/ (bic_scale * 10);

		/* BIC TCP Parameters */
		struct bictcp {
		__u32 cnt; /* increase cwnd by 1 after ACKs */
		__u32 last_max_cwnd; /* last maximum snd_cwnd */
		__u32 last_cwnd; /* the last snd_cwnd */
		__u32 last_time; /* time when updated last_cwnd */
		__u32 bic_origin_point;/* origin point of bic function */
		__u32 bic_K; /* time to origin point
		from the beginning of the current epoch */
		__u32 delay_min; /* min delay (usec) */
		__u32 epoch_start; /* beginning of an epoch */
		__u32 ack_cnt; /* number of acks */
		__u32 tcp_cwnd; /* estimated tcp cwnd */
		__u16 unused;
		__u8 sample_cnt; /* number of samples to decide curr_rtt */
		__u8 found; /* the exit point is found? */
		__u32 round_start; /* beginning of each round */
		__u32 end_seq; /* end_seq of the round */
		__u32 last_ack; /* last time when the ACK spacing is close */
		__u32 curr_rtt; /* the minimum rtt of current round */
		};

		static inline void bictcp_reset(struct bictcp *ca)
		{
		ca->cnt = 0;
		ca->last_max_cwnd = 0;
		ca->last_cwnd = 0;
		ca->last_time = 0;
		ca->bic_origin_point = 0;
		ca->bic_K = 0;
		ca->delay_min = 0;
		ca->epoch_start = 0;
		ca->ack_cnt = 0;
		ca->tcp_cwnd = 0;
		ca->found = 0;
		}

		extern unsigned long CONFIG_HZ __kconfig;
		#define HZ CONFIG_HZ
		#define USEC_PER_MSEC 1000UL
		#define USEC_PER_SEC 1000000UL
		#define USEC_PER_JIFFY (USEC_PER_SEC / HZ)

		static __always_inline __u64 div64_u64(__u64 dividend, __u64 divisor)
		{
		return dividend / divisor;
		}

		#define div64_ul div64_u64

		#define BITS_PER_U64 (sizeof(__u64) * 8)
		static __always_inline int fls64(__u64 x)
		{
		int num = BITS_PER_U64 - 1;

		if (x == 0)
		return 0;

		if (!(x & (~0ull << (BITS_PER_U64-32)))) {
		num -= 32;
		x <<= 32;
		}
		if (!(x & (~0ull << (BITS_PER_U64-16)))) {
		num -= 16;
		x <<= 16;
		}
		if (!(x & (~0ull << (BITS_PER_U64-8)))) {
		num -= 8;
		x <<= 8;
		}
		if (!(x & (~0ull << (BITS_PER_U64-4)))) {
		num -= 4;
		x <<= 4;
		}
		if (!(x & (~0ull << (BITS_PER_U64-2)))) {
		num -= 2;
		x <<= 2;
		}
		if (!(x & (~0ull << (BITS_PER_U64-1))))
		num -= 1;

		return num + 1;
		}

		static __always_inline __u32 bictcp_clock_us(const struct sock *sk)
		{
		return tcp_sk(sk)->tcp_mstamp;
		}

		static __always_inline void bictcp_hystart_reset(struct sock *sk)
		{
		struct tcp_sock *tp = tcp_sk(sk);
		struct bictcp *ca = inet_csk_ca(sk);

		ca->round_start = ca->last_ack = bictcp_clock_us(sk);
		ca->end_seq = tp->snd_nxt;
		ca->curr_rtt = ~0U;
		ca->sample_cnt = 0;
		}

		/* "struct_ops/" prefix is not a requirement
		* It will be recognized as BPF_PROG_TYPE_STRUCT_OPS
		* as long as it is used in one of the func ptr
		* under SEC(".struct_ops").
		*/
		SEC("struct_ops/bictcp_init")
		void BPF_PROG(bictcp_init, struct sock *sk)
		{
		struct bictcp *ca = inet_csk_ca(sk);

		bictcp_reset(ca);

		if (hystart)
		bictcp_hystart_reset(sk);

		if (!hystart && initial_ssthresh)
		tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
		}

		/* No prefix in SEC will also work.
		* The remaining tcp-cubic functions have an easier way.
		*/
		SEC("no-sec-prefix-bictcp_cwnd_event")
		void BPF_PROG(bictcp_cwnd_event, struct sock *sk, enum tcp_ca_event event)
		{
		if (event == CA_EVENT_TX_START) {
		struct bictcp *ca = inet_csk_ca(sk);
		__u32 now = tcp_jiffies32;
		__s32 delta;

		delta = now - tcp_sk(sk)->lsndtime;

		/* We were application limited (idle) for a while.
		* Shift epoch_start to keep cwnd growth to cubic curve.
		*/
		if (ca->epoch_start && delta > 0) {
		ca->epoch_start += delta;
		if (after(ca->epoch_start, now))
		ca->epoch_start = now;
		}
		return;
		}
		}

		/*
		* cbrt(x) MSB values for x MSB values in [0..63].
		* Precomputed then refined by hand - Willy Tarreau
		*
		* For x in [0..63],
		* v = cbrt(x << 18) - 1
		* cbrt(x) = (v[x] + 10) >> 6
		*/
		static const __u8 v[] = {
		/* 0x00 */ 0, 54, 54, 54, 118, 118, 118, 118,
		/* 0x08 */ 123, 129, 134, 138, 143, 147, 151, 156,
		/* 0x10 */ 157, 161, 164, 168, 170, 173, 176, 179,
		/* 0x18 */ 181, 185, 187, 190, 192, 194, 197, 199,
		/* 0x20 */ 200, 202, 204, 206, 209, 211, 213, 215,
		/* 0x28 */ 217, 219, 221, 222, 224, 225, 227, 229,
		/* 0x30 */ 231, 232, 234, 236, 237, 239, 240, 242,
		/* 0x38 */ 244, 245, 246, 248, 250, 251, 252, 254,
		};

		/* calculate the cubic root of x using a table lookup followed by one
		* Newton-Raphson iteration.
		* Avg err ~= 0.195%
		*/
		static __always_inline __u32 cubic_root(__u64 a)
		{
		__u32 x, b, shift;

		if (a < 64) {
		/* a in [0..63] */
		return ((__u32)v[(__u32)a] + 35) >> 6;
		}

		b = fls64(a);
		b = ((b * 84) >> 8) - 1;
		shift = (a >> (b * 3));

		/* it is needed for verifier's bound check on v */
		if (shift >= 64)
		return 0;

		x = ((__u32)(((__u32)v[shift] + 10) << b)) >> 6;

		/*
		* Newton-Raphson iteration
		* 2
		* x = ( 2 * x + a / x ) / 3
		* k+1 k k
		*/
		x = (2 * x + (__u32)div64_u64(a, (__u64)x * (__u64)(x - 1)));
		x = ((x * 341) >> 10);
		return x;
		}

		/*
		* Compute congestion window to use.
		*/
		static __always_inline void bictcp_update(struct bictcp *ca, __u32 cwnd,
		__u32 acked)
		{
		__u32 delta, bic_target, max_cnt;
		__u64 offs, t;

		ca->ack_cnt += acked; /* count the number of ACKed packets */

		if (ca->last_cwnd == cwnd &&
		(__s32)(tcp_jiffies32 - ca->last_time) <= HZ / 32)
		return;

		/* The CUBIC function can update ca->cnt at most once per jiffy.
		* On all cwnd reduction events, ca->epoch_start is set to 0,
		* which will force a recalculation of ca->cnt.
		*/
		if (ca->epoch_start && tcp_jiffies32 == ca->last_time)
		goto tcp_friendliness;

		ca->last_cwnd = cwnd;
		ca->last_time = tcp_jiffies32;

		if (ca->epoch_start == 0) {
		ca->epoch_start = tcp_jiffies32; /* record beginning */
		ca->ack_cnt = acked; /* start counting */
		ca->tcp_cwnd = cwnd; /* syn with cubic */

		if (ca->last_max_cwnd <= cwnd) {
		ca->bic_K = 0;
		ca->bic_origin_point = cwnd;
		} else {
		/* Compute new K based on
		* (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ)
		*/
		ca->bic_K = cubic_root(cube_factor
		* (ca->last_max_cwnd - cwnd));
		ca->bic_origin_point = ca->last_max_cwnd;
		}
		}

		/* cubic function - calc*/
		/* calculate c * time^3 / rtt,
		* while considering overflow in calculation of time^3
		* (so time^3 is done by using 64 bit)
		* and without the support of division of 64bit numbers
		* (so all divisions are done by using 32 bit)
		* also NOTE the unit of those veriables
		* time = (t - K) / 2^bictcp_HZ
		* c = bic_scale >> 10
		* rtt = (srtt >> 3) / HZ
		* !!! The following code does not have overflow problems,
		* if the cwnd < 1 million packets !!!
		*/

		t = (__s32)(tcp_jiffies32 - ca->epoch_start) * USEC_PER_JIFFY;
		t += ca->delay_min;
		/* change the unit from usec to bictcp_HZ */
		t <<= BICTCP_HZ;
		t /= USEC_PER_SEC;

		if (t < ca->bic_K) /* t - K */
		offs = ca->bic_K - t;
		else
		offs = t - ca->bic_K;

		/* c/rtt * (t-K)^3 */
		delta = (cube_rtt_scale * offs * offs * offs) >> (10+3*BICTCP_HZ);
		if (t < ca->bic_K) /* below origin*/
		bic_target = ca->bic_origin_point - delta;
		else /* above origin*/
		bic_target = ca->bic_origin_point + delta;

		/* cubic function - calc bictcp_cnt*/
		if (bic_target > cwnd) {
		ca->cnt = cwnd / (bic_target - cwnd);
		} else {
		ca->cnt = 100 * cwnd; /* very small increment*/
		}

		/*
		* The initial growth of cubic function may be too conservative
		* when the available bandwidth is still unknown.
		*/
		if (ca->last_max_cwnd == 0 && ca->cnt > 20)
		ca->cnt = 20; /* increase cwnd 5% per RTT */

		tcp_friendliness:
		/* TCP Friendly */
		if (tcp_friendliness) {
		__u32 scale = beta_scale;
		__u32 n;

		/* update tcp cwnd */
		delta = (cwnd * scale) >> 3;
		if (ca->ack_cnt > delta && delta) {
		n = ca->ack_cnt / delta;
		ca->ack_cnt -= n * delta;
		ca->tcp_cwnd += n;
		}

		if (ca->tcp_cwnd > cwnd) { /* if bic is slower than tcp */
		delta = ca->tcp_cwnd - cwnd;
		max_cnt = cwnd / delta;
		if (ca->cnt > max_cnt)
		ca->cnt = max_cnt;
		}
		}

		/* The maximum rate of cwnd increase CUBIC allows is 1 packet per
		* 2 packets ACKed, meaning cwnd grows at 1.5x per RTT.
		*/
		ca->cnt = max(ca->cnt, 2U);
		}

		/* Or simply use the BPF_STRUCT_OPS to avoid the SEC boiler plate. */
		void BPF_STRUCT_OPS(bictcp_cong_avoid, struct sock *sk, __u32 ack, __u32 acked)
		{
		struct tcp_sock *tp = tcp_sk(sk);
		struct bictcp *ca = inet_csk_ca(sk);

		if (!tcp_is_cwnd_limited(sk))
		return;

		if (tcp_in_slow_start(tp)) {
		if (hystart && after(ack, ca->end_seq))
		bictcp_hystart_reset(sk);
		acked = tcp_slow_start(tp, acked);
		if (!acked)
		return;
		}
		bictcp_update(ca, tp->snd_cwnd, acked);
		tcp_cong_avoid_ai(tp, ca->cnt, acked);
		}

		__u32 BPF_STRUCT_OPS(bictcp_recalc_ssthresh, struct sock *sk)
		{
		const struct tcp_sock *tp = tcp_sk(sk);
		struct bictcp *ca = inet_csk_ca(sk);

		ca->epoch_start = 0; /* end of epoch */

		/* Wmax and fast convergence */
		if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
		ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
		/ (2 * BICTCP_BETA_SCALE);
		else
		ca->last_max_cwnd = tp->snd_cwnd;

		return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
		}

		void BPF_STRUCT_OPS(bictcp_state, struct sock *sk, __u8 new_state)
		{
		if (new_state == TCP_CA_Loss) {
		bictcp_reset(inet_csk_ca(sk));
		bictcp_hystart_reset(sk);
		}
		}

		#define GSO_MAX_SIZE 65536

		/* Account for TSO/GRO delays.
		* Otherwise short RTT flows could get too small ssthresh, since during
		* slow start we begin with small TSO packets and ca->delay_min would
		* not account for long aggregation delay when TSO packets get bigger.
		* Ideally even with a very small RTT we would like to have at least one
		* TSO packet being sent and received by GRO, and another one in qdisc layer.
		* We apply another 100% factor because @rate is doubled at this point.
		* We cap the cushion to 1ms.
		*/
		static __always_inline __u32 hystart_ack_delay(struct sock *sk)
		{
		unsigned long rate;

		rate = sk->sk_pacing_rate;
		if (!rate)
		return 0;
		return min((__u64)USEC_PER_MSEC,
		div64_ul((__u64)GSO_MAX_SIZE * 4 * USEC_PER_SEC, rate));
		}

		static __always_inline void hystart_update(struct sock *sk, __u32 delay)
		{
		struct tcp_sock *tp = tcp_sk(sk);
		struct bictcp *ca = inet_csk_ca(sk);
		__u32 threshold;

		if (hystart_detect & HYSTART_ACK_TRAIN) {
		__u32 now = bictcp_clock_us(sk);

		/* first detection parameter - ack-train detection */
		if ((__s32)(now - ca->last_ack) <= hystart_ack_delta_us) {
		ca->last_ack = now;

		threshold = ca->delay_min + hystart_ack_delay(sk);

		/* Hystart ack train triggers if we get ack past
		* ca->delay_min/2.
		* Pacing might have delayed packets up to RTT/2
		* during slow start.
		*/
		if (sk->sk_pacing_status == SK_PACING_NONE)
		threshold >>= 1;

		if ((__s32)(now - ca->round_start) > threshold) {
		ca->found = 1;
		tp->snd_ssthresh = tp->snd_cwnd;
		}
		}
		}

		if (hystart_detect & HYSTART_DELAY) {
		/* obtain the minimum delay of more than sampling packets */
		if (ca->sample_cnt < HYSTART_MIN_SAMPLES) {
		if (ca->curr_rtt > delay)
		ca->curr_rtt = delay;

		ca->sample_cnt++;
		} else {
		if (ca->curr_rtt > ca->delay_min +
		HYSTART_DELAY_THRESH(ca->delay_min >> 3)) {
		ca->found = 1;
		tp->snd_ssthresh = tp->snd_cwnd;
		}
		}
		}
		}

		void BPF_STRUCT_OPS(bictcp_acked, struct sock *sk,
		const struct ack_sample *sample)
		{
		const struct tcp_sock *tp = tcp_sk(sk);
		struct bictcp *ca = inet_csk_ca(sk);
		__u32 delay;

		/* Some calls are for duplicates without timetamps */
		if (sample->rtt_us < 0)
		return;

		/* Discard delay samples right after fast recovery */
		if (ca->epoch_start && (__s32)(tcp_jiffies32 - ca->epoch_start) < HZ)
		return;

		delay = sample->rtt_us;
		if (delay == 0)
		delay = 1;

		/* first time call or link delay decreases */
		if (ca->delay_min == 0 \|\| ca->delay_min > delay)
		ca->delay_min = delay;

		/* hystart triggers when cwnd is larger than some threshold */
		if (!ca->found && tcp_in_slow_start(tp) && hystart &&
		tp->snd_cwnd >= hystart_low_window)
		hystart_update(sk, delay);
		}

		__u32 BPF_STRUCT_OPS(tcp_reno_undo_cwnd, struct sock *sk)
		{
		const struct tcp_sock *tp = tcp_sk(sk);

		return max(tp->snd_cwnd, tp->prior_cwnd);
		}

		SEC(".struct_ops")
		struct tcp_congestion_ops cubic = {
		.init = (void *)bictcp_init,
		.ssthresh = (void *)bictcp_recalc_ssthresh,
		.cong_avoid = (void *)bictcp_cong_avoid,
		.set_state = (void *)bictcp_state,
		.undo_cwnd = (void *)tcp_reno_undo_cwnd,
		.cwnd_event = (void *)bictcp_cwnd_event,
		.pkts_acked = (void *)bictcp_acked,
		.name = "bpf_cubic",
		};

Admin message