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litespeed-quic/src/liblsquic/lsquic_cubic.c

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/* Copyright (c) 2017 - 2022 LiteSpeed Technologies Inc. See LICENSE. */
/*
* lsquic_cubic.c -- LSQUIC CUBIC implementation.
*/
#include <inttypes.h>
#include <math.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include <sys/queue.h>
#ifdef WIN32
#include <vc_compat.h>
#endif
#include "lsquic_int_types.h"
#include "lsquic_types.h"
#include "lsquic_hash.h"
#include "lsquic_util.h"
#include "lsquic_cong_ctl.h"
#include "lsquic_sfcw.h"
#include "lsquic_conn_flow.h"
#include "lsquic_varint.h"
#include "lsquic_hq.h"
#include "lsquic_stream.h"
#include "lsquic_rtt.h"
#include "lsquic_conn_public.h"
#include "lsquic_packet_common.h"
#include "lsquic_packet_out.h"
#include "lsquic_cubic.h"
#define LSQUIC_LOGGER_MODULE LSQLM_CUBIC
#define LSQUIC_LOG_CONN_ID lsquic_conn_log_cid(cubic->cu_conn)
#include "lsquic_logger.h"
#define FAST_CONVERGENCE 1
#define BETA 205 /* 205/1024 */
#define C 410 /* 410/1024 */
#define TWO_MINUS_BETA_OVER_TWO 922 /* 922/1024 */
#define ONE_MINUS_BETA 819 /* 819/1024 */
#define ONE_OVER_C 2560 /* 2560/1024 */
static void
cubic_reset (struct lsquic_cubic *cubic)
{
memset(cubic, 0, offsetof(struct lsquic_cubic, cu_conn));
cubic->cu_cwnd = 32 * TCP_MSS;
cubic->cu_last_max_cwnd = 32 * TCP_MSS;
cubic->cu_tcp_cwnd = 32 * TCP_MSS;
}
static void
cubic_update (struct lsquic_cubic *cubic, lsquic_time_t now, unsigned n_bytes)
{
double delta_t, t;
lsquic_time_t target;
if (0 == cubic->cu_epoch_start)
{
cubic->cu_epoch_start = now;
if (cubic->cu_cwnd < cubic->cu_last_max_cwnd)
{
cubic->cu_K = cbrt(cubic->cu_last_max_cwnd / TCP_MSS / 2);
cubic->cu_origin_point = cubic->cu_last_max_cwnd;
}
else
{
cubic->cu_K = 0;
cubic->cu_origin_point = cubic->cu_cwnd;
}
LSQ_DEBUG("cwnd: %lu; last_max_cwnd: %lu; K: %lf; origin_point: %lu",
cubic->cu_cwnd, cubic->cu_last_max_cwnd, cubic->cu_K, cubic->cu_origin_point);
}
delta_t = (double) (now + cubic->cu_min_delay - cubic->cu_epoch_start) / 1000000;
if (delta_t < cubic->cu_K)
{
t = cubic->cu_K - delta_t;
target = cubic->cu_origin_point - t * t * t * 0.4 * TCP_MSS;
LSQ_DEBUG("delta_t: %lf; t: %lf; target 1: %"PRIu64, delta_t, t, target);
}
else
{
t = delta_t - cubic->cu_K;
target = cubic->cu_origin_point + t * t * t * 0.4 * TCP_MSS;
LSQ_DEBUG("target 2: %"PRIu64, target);
}
if (cubic->cu_flags & CU_TCP_FRIENDLY)
{
cubic->cu_tcp_cwnd += n_bytes * TCP_MSS * ONE_MINUS_BETA / 1024
/ cubic->cu_tcp_cwnd;
LSQ_DEBUG("delta_t: %lf; last_max: %lu; cu_tcp_cwnd: %lu; target: "
"%"PRIu64"; over: %d; left: %d", delta_t, cubic->cu_last_max_cwnd,
cubic->cu_tcp_cwnd, target, cubic->cu_tcp_cwnd > target,
delta_t < cubic->cu_K);
if (cubic->cu_tcp_cwnd > target)
target = cubic->cu_tcp_cwnd;
}
if (target == 0)
target = TCP_MSS;
cubic->cu_cwnd = target;
}
void
lsquic_cubic_set_flags (struct lsquic_cubic *cubic, enum cubic_flags flags)
{
LSQ_DEBUG("%s(cubic, 0x%X)", __func__, flags);
cubic->cu_flags = flags;
}
static void
lsquic_cubic_init (void *cong_ctl, const struct lsquic_conn_public *conn_pub,
enum quic_ft_bit UNUSED_retx_frames)
{
struct lsquic_cubic *const cubic = cong_ctl;
cubic_reset(cubic);
cubic->cu_ssthresh = 10000 * TCP_MSS; /* Emulate "unbounded" slow start */
cubic->cu_conn = conn_pub->lconn;
cubic->cu_rtt_stats = &conn_pub->rtt_stats;
cubic->cu_flags = DEFAULT_CUBIC_FLAGS;
#ifndef NDEBUG
const char *s;
s = getenv("LSQUIC_CUBIC_SAMPLING_RATE");
if (s)
cubic->cu_sampling_rate = atoi(s);
else
#endif
cubic->cu_sampling_rate = 100000;
LSQ_DEBUG("%s(cubic, $conn)", __func__);
LSQ_INFO("initialized");
}
static void
lsquic_cubic_reinit (void *cong_ctl)
{
struct lsquic_cubic *const cubic = cong_ctl;
cubic_reset(cubic);
cubic->cu_ssthresh = 10000 * TCP_MSS; /* Emulate "unbounded" slow start */
LSQ_DEBUG("re-initialized");
}
#define LOG_CWND(c) do { \
if (LSQ_LOG_ENABLED(LSQ_LOG_INFO)) { \
lsquic_time_t now = lsquic_time_now(); \
now -= now % (c)->cu_sampling_rate; \
if (now > (c)->cu_last_logged) { \
LSQ_INFO("CWND: %lu", (c)->cu_cwnd); \
(c)->cu_last_logged = now; \
} \
} \
} while (0)
static void
lsquic_cubic_was_quiet (void *cong_ctl, lsquic_time_t now, uint64_t in_flight)
{
struct lsquic_cubic *const cubic = cong_ctl;
LSQ_DEBUG("%s(cubic, %"PRIu64")", __func__, now);
cubic->cu_epoch_start = 0;
}
static void
lsquic_cubic_ack (void *cong_ctl, struct lsquic_packet_out *packet_out,
unsigned n_bytes, lsquic_time_t now_time, int app_limited)
{
struct lsquic_cubic *const cubic = cong_ctl;
lsquic_time_t rtt;
rtt = now_time - packet_out->po_sent;
LSQ_DEBUG("%s(cubic, %"PRIu64", %"PRIu64", %d, %u)", __func__, now_time, rtt,
app_limited, n_bytes);
if (0 == cubic->cu_min_delay || rtt < cubic->cu_min_delay)
{
cubic->cu_min_delay = rtt;
LSQ_INFO("min_delay: %"PRIu64, rtt);
}
if (cubic->cu_cwnd <= cubic->cu_ssthresh)
{
cubic->cu_cwnd += TCP_MSS;
LSQ_DEBUG("ACK: slow threshold, cwnd: %lu", cubic->cu_cwnd);
}
else if (!app_limited)
{
cubic_update(cubic, now_time, n_bytes);
LSQ_DEBUG("ACK: cwnd: %lu", cubic->cu_cwnd);
}
LOG_CWND(cubic);
}
static void
lsquic_cubic_loss (void *cong_ctl)
{
struct lsquic_cubic *const cubic = cong_ctl;
LSQ_DEBUG("%s(cubic)", __func__);
cubic->cu_epoch_start = 0;
if (FAST_CONVERGENCE && cubic->cu_cwnd < cubic->cu_last_max_cwnd)
cubic->cu_last_max_cwnd = cubic->cu_cwnd * TWO_MINUS_BETA_OVER_TWO / 1024;
else
cubic->cu_last_max_cwnd = cubic->cu_cwnd;
cubic->cu_cwnd = cubic->cu_cwnd * ONE_MINUS_BETA / 1024;
cubic->cu_tcp_cwnd = cubic->cu_cwnd;
cubic->cu_ssthresh = cubic->cu_cwnd;
LSQ_INFO("loss detected, last_max_cwnd: %lu, cwnd: %lu",
cubic->cu_last_max_cwnd, cubic->cu_cwnd);
LOG_CWND(cubic);
}
static void
lsquic_cubic_timeout (void *cong_ctl)
{
struct lsquic_cubic *const cubic = cong_ctl;
unsigned long cwnd;
cwnd = cubic->cu_cwnd;
LSQ_DEBUG("%s(cubic)", __func__);
cubic_reset(cubic);
cubic->cu_ssthresh = cwnd / 2;
cubic->cu_tcp_cwnd = 2 * TCP_MSS;
cubic->cu_cwnd = 2 * TCP_MSS;
LSQ_INFO("timeout, cwnd: %lu", cubic->cu_cwnd);
LOG_CWND(cubic);
}
static void
lsquic_cubic_cleanup (void *cong_ctl)
{
}
static uint64_t
lsquic_cubic_get_cwnd (void *cong_ctl)
{
struct lsquic_cubic *const cubic = cong_ctl;
return cubic->cu_cwnd;
}
static int
in_slow_start (void *cong_ctl)
{
struct lsquic_cubic *const cubic = cong_ctl;
return cubic->cu_cwnd < cubic->cu_ssthresh;
}
static uint64_t
lsquic_cubic_pacing_rate (void *cong_ctl, int in_recovery)
{
struct lsquic_cubic *const cubic = cong_ctl;
uint64_t bandwidth, pacing_rate;
lsquic_time_t srtt;
srtt = lsquic_rtt_stats_get_srtt(cubic->cu_rtt_stats);
if (srtt == 0)
srtt = 50000;
bandwidth = cubic->cu_cwnd * 1000000 / srtt;
if (in_slow_start(cubic))
pacing_rate = bandwidth * 2;
else if (in_recovery)
pacing_rate = bandwidth;
else
pacing_rate = bandwidth + bandwidth / 4;
return pacing_rate;
}
const struct cong_ctl_if lsquic_cong_cubic_if =
{
.cci_ack = lsquic_cubic_ack,
.cci_cleanup = lsquic_cubic_cleanup,
.cci_get_cwnd = lsquic_cubic_get_cwnd,
.cci_init = lsquic_cubic_init,
.cci_pacing_rate = lsquic_cubic_pacing_rate,
.cci_loss = lsquic_cubic_loss,
.cci_reinit = lsquic_cubic_reinit,
.cci_timeout = lsquic_cubic_timeout,
.cci_was_quiet = lsquic_cubic_was_quiet,
};
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