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QUIC: added rtt estimation.

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According to the quic-recovery 29, Section 5: Estimating the Round-Trip Time.

Currently, integer arithmetics is used, which loses sub-millisecond accuracy.
This commit is contained in:
Vladimir Homutov 2020-07-16 15:44:06 +03:00
parent 2346ee29e1
commit 32fd0a7b44
2 changed files with 96 additions and 9 deletions
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102
src/event/ngx_event_quic.c
View File

@ -99,6 +99,11 @@ struct ngx_quic_connection_s {
ngx_queue_t free_frames;
ngx_msec_t last_cc;
ngx_msec_t latest_rtt;
ngx_msec_t avg_rtt;
ngx_msec_t min_rtt;
ngx_msec_t rttvar;
#if (NGX_DEBUG)
ngx_uint_t nframes;
#endif
@ -189,7 +194,10 @@ static ngx_int_t ngx_quic_send_new_token(ngx_connection_t *c);
static ngx_int_t ngx_quic_handle_ack_frame(ngx_connection_t *c,
ngx_quic_header_t *pkt, ngx_quic_ack_frame_t *f);
static ngx_int_t ngx_quic_handle_ack_frame_range(ngx_connection_t *c,
ngx_quic_send_ctx_t *ctx, uint64_t min, uint64_t max);
ngx_quic_send_ctx_t *ctx, uint64_t min, uint64_t max,
ngx_msec_t *send_time);
static void ngx_quic_rtt_sample(ngx_connection_t *c, ngx_quic_ack_frame_t *ack,
enum ssl_encryption_level_t level, ngx_msec_t send_time);
static void ngx_quic_handle_stream_ack(ngx_connection_t *c,
ngx_quic_frame_t *f);
@ -665,6 +673,14 @@ ngx_quic_new_connection(ngx_connection_t *c, ngx_ssl_t *ssl, ngx_quic_tp_t *tp,
ngx_queue_init(&qc->free_frames);
qc->avg_rtt = NGX_QUIC_INITIAL_RTT;
qc->rttvar = NGX_QUIC_INITIAL_RTT / 2;
qc->min_rtt = NGX_TIMER_INFINITE;
/*
* qc->latest_rtt = 0
*/
qc->retransmit.log = c->log;
qc->retransmit.data = c;
qc->retransmit.handler = ngx_quic_retransmit_handler;
@ -2210,6 +2226,7 @@ ngx_quic_handle_ack_frame(ngx_connection_t *c, ngx_quic_header_t *pkt,
ssize_t n;
u_char *pos, *end;
uint64_t gap, range;
ngx_msec_t send_time;
ngx_uint_t i, min, max;
ngx_quic_send_ctx_t *ctx;
@ -2234,7 +2251,9 @@ ngx_quic_handle_ack_frame(ngx_connection_t *c, ngx_quic_header_t *pkt,
min = ack->largest - ack->first_range;
max = ack->largest;
if (ngx_quic_handle_ack_frame_range(c, ctx, min, max) != NGX_OK) {
if (ngx_quic_handle_ack_frame_range(c, ctx, min, max, &send_time)
!= NGX_OK)
{
return NGX_ERROR;
}
@ -2243,6 +2262,18 @@ ngx_quic_handle_ack_frame(ngx_connection_t *c, ngx_quic_header_t *pkt,
ctx->largest_ack = max;
ngx_log_debug1(NGX_LOG_DEBUG_EVENT, c->log, 0,
"quic updated largest received ack: %ui", max);
/*
* An endpoint generates an RTT sample on receiving an
* ACK frame that meets the following two conditions:
*
* - the largest acknowledged packet number is newly acknowledged
* - at least one of the newly acknowledged packets was ack-eliciting.
*/
if (send_time != NGX_TIMER_INFINITE) {
ngx_quic_rtt_sample(c, ack, pkt->level, send_time);
}
}
pos = ack->ranges_start;
@ -2274,7 +2305,9 @@ ngx_quic_handle_ack_frame(ngx_connection_t *c, ngx_quic_header_t *pkt,
min = max - range + 1;
if (ngx_quic_handle_ack_frame_range(c, ctx, min, max) != NGX_OK) {
if (ngx_quic_handle_ack_frame_range(c, ctx, min, max, &send_time)
!= NGX_OK)
{
return NGX_ERROR;
}
}
@ -2285,8 +2318,9 @@ ngx_quic_handle_ack_frame(ngx_connection_t *c, ngx_quic_header_t *pkt,
static ngx_int_t
ngx_quic_handle_ack_frame_range(ngx_connection_t *c, ngx_quic_send_ctx_t *ctx,
uint64_t min, uint64_t max)
uint64_t min, uint64_t max, ngx_msec_t *send_time)
{
uint64_t found_num;
ngx_uint_t found;
ngx_queue_t *q;
ngx_quic_frame_t *f;
@ -2294,26 +2328,30 @@ ngx_quic_handle_ack_frame_range(ngx_connection_t *c, ngx_quic_send_ctx_t *ctx,
qc = c->quic;
*send_time = NGX_TIMER_INFINITE;
found = 0;
found_num = 0;
q = ngx_queue_head(&ctx->sent);
q = ngx_queue_last(&ctx->sent);
while (q != ngx_queue_sentinel(&ctx->sent)) {
f = ngx_queue_data(q, ngx_quic_frame_t, queue);
q = ngx_queue_prev(q);
if (f->pnum >= min && f->pnum <= max) {
ngx_quic_congestion_ack(c, f);
ngx_quic_handle_stream_ack(c, f);
q = ngx_queue_next(q);
if (f->pnum > found_num || !found) {
*send_time = f->last;
found_num = f->pnum;
}
ngx_queue_remove(&f->queue);
ngx_quic_free_frame(c, f);
found = 1;
} else {
q = ngx_queue_next(q);
}
}
@ -2342,6 +2380,52 @@ ngx_quic_handle_ack_frame_range(ngx_connection_t *c, ngx_quic_send_ctx_t *ctx,
}
static void
ngx_quic_rtt_sample(ngx_connection_t *c, ngx_quic_ack_frame_t *ack,
enum ssl_encryption_level_t level, ngx_msec_t send_time)
{
ngx_msec_t latest_rtt, ack_delay, adjusted_rtt, rttvar_sample;
ngx_quic_connection_t *qc;
qc = c->quic;
latest_rtt = ngx_current_msec - send_time;
qc->latest_rtt = latest_rtt;
if (qc->min_rtt == NGX_TIMER_INFINITE) {
qc->min_rtt = latest_rtt;
qc->avg_rtt = latest_rtt;
qc->rttvar = latest_rtt / 2;
} else {
qc->min_rtt = ngx_min(qc->min_rtt, latest_rtt);
if (level == ssl_encryption_application) {
ack_delay = ack->delay * (1 << qc->ctp.ack_delay_exponent) / 1000;
ack_delay = ngx_min(ack_delay, qc->ctp.max_ack_delay);
} else {
ack_delay = 0;
}
adjusted_rtt = latest_rtt;
if (qc->min_rtt + ack_delay < latest_rtt) {
adjusted_rtt -= ack_delay;
}
qc->avg_rtt = 0.875 * qc->avg_rtt + 0.125 * adjusted_rtt;
rttvar_sample = ngx_abs((ngx_msec_int_t) (qc->avg_rtt - adjusted_rtt));
qc->rttvar = 0.75 * qc->rttvar + 0.25 * rttvar_sample;
}
ngx_log_debug4(NGX_LOG_DEBUG_EVENT, c->log, 0,
"quic rtt sample: latest %M, min %M, avg %M, var %M",
latest_rtt, qc->min_rtt, qc->avg_rtt, qc->rttvar);
}
static void
ngx_quic_handle_stream_ack(ngx_connection_t *c, ngx_quic_frame_t *f)
{

3
src/event/ngx_event_quic.h
View File

@ -41,6 +41,9 @@
#define NGX_QUIC_MAX_TOKEN_SIZE 32
/* sizeof(struct in6_addr) + sizeof(ngx_msec_t) up to AES-256 block size */
/* quic-recovery, section 6.2.2, kInitialRtt */
#define NGX_QUIC_INITIAL_RTT 333 /* ms */
#define NGX_QUIC_HARDCODED_PTO 1000 /* 1s, TODO: collect */
#define NGX_QUIC_CC_MIN_INTERVAL 1000 /* 1s */