lsquic_rtt.c revision a74702c6
1a74702c6SGeorge Wang/* Copyright (c) 2017 - 2022 LiteSpeed Technologies Inc. See LICENSE. */ 250aadb33SDmitri Tikhonov/* 350aadb33SDmitri Tikhonov * lsquic_rtt.c -- RTT calculation 450aadb33SDmitri Tikhonov */ 550aadb33SDmitri Tikhonov 650aadb33SDmitri Tikhonov#include <stdlib.h> 750aadb33SDmitri Tikhonov#include <string.h> 8461e84d8SAmol Deshpande#ifndef WIN32 950aadb33SDmitri Tikhonov#include <sys/time.h> 10461e84d8SAmol Deshpande#endif 1150aadb33SDmitri Tikhonov 1250aadb33SDmitri Tikhonov#include "lsquic_int_types.h" 1350aadb33SDmitri Tikhonov#include "lsquic_rtt.h" 1450aadb33SDmitri Tikhonov 1550aadb33SDmitri Tikhonov/* See RFC 2988 */ 1650aadb33SDmitri Tikhonov 1750aadb33SDmitri Tikhonov#define ALPHA_SHIFT 3 /* Alpha is 1/8 */ 1850aadb33SDmitri Tikhonov#define BETA_SHIFT 2 /* Beta is 1/4 */ 1950aadb33SDmitri Tikhonov 2050aadb33SDmitri Tikhonov 2150aadb33SDmitri Tikhonovvoid 2250aadb33SDmitri Tikhonovlsquic_rtt_stats_update (struct lsquic_rtt_stats *stats, 2350aadb33SDmitri Tikhonov lsquic_time_t send_delta, lsquic_time_t lack_delta) 2450aadb33SDmitri Tikhonov{ 2550aadb33SDmitri Tikhonov if (send_delta > lack_delta) 2650aadb33SDmitri Tikhonov send_delta -= lack_delta; 2750aadb33SDmitri Tikhonov if (stats->srtt) { 2850aadb33SDmitri Tikhonov stats->rttvar -= stats->rttvar >> BETA_SHIFT; 2950aadb33SDmitri Tikhonov // FIXED: subtracting unsigned (the (int) cast gets repromoted to uint64_t 3050aadb33SDmitri Tikhonov // made abs() irrelevant and allowed overflow. instead cast the difference 3150aadb33SDmitri Tikhonov // to a signed int64 and use labs() to get abs val. 3250aadb33SDmitri Tikhonov stats->rttvar += (llabs((int64_t) (send_delta - stats->srtt))) 3350aadb33SDmitri Tikhonov >> BETA_SHIFT; 3450aadb33SDmitri Tikhonov stats->srtt -= stats->srtt >> ALPHA_SHIFT; 3550aadb33SDmitri Tikhonov stats->srtt += send_delta >> ALPHA_SHIFT; 365392f7a3SLiteSpeed Tech if (send_delta < stats->min_rtt) 375392f7a3SLiteSpeed Tech stats->min_rtt = send_delta; 3850aadb33SDmitri Tikhonov } else { 3950aadb33SDmitri Tikhonov /* First measurement */ 4050aadb33SDmitri Tikhonov stats->srtt = send_delta; 4150aadb33SDmitri Tikhonov stats->rttvar = send_delta >> 1; 425392f7a3SLiteSpeed Tech stats->min_rtt = send_delta; 4350aadb33SDmitri Tikhonov } 4450aadb33SDmitri Tikhonov} 45