-
-/* Detect low utilization in congestion avoidance */
-static inline void bictcp_low_utilization(struct sock *sk, int flag)
-{
- const struct tcp_sock *tp = tcp_sk(sk);
- struct bictcp *ca = inet_csk_ca(sk);
- u32 dist, delay;
-
- /* No time stamp */
- if (!(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) ||
- /* Discard delay samples right after fast recovery */
- tcp_time_stamp < ca->epoch_start + HZ ||
- /* this delay samples may not be accurate */
- flag == 0) {
- ca->last_delay = 0;
- goto notlow;
- }
-
- delay = ca->last_delay<<3; /* use the same scale as tp->srtt*/
- ca->last_delay = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
- if (delay == 0) /* no previous delay sample */
- goto notlow;
-
- /* first time call or link delay decreases */
- if (ca->delay_min == 0 || ca->delay_min > delay) {
- ca->delay_min = ca->delay_max = delay;
- goto notlow;
- }
-
- if (ca->delay_max < delay)
- ca->delay_max = delay;
-
- /* utilization is low, if avg delay < dist*threshold
- for checking_period time */
- dist = ca->delay_max - ca->delay_min;
- if (dist <= ca->delay_min>>6 ||
- tp->srtt - ca->delay_min >= (dist*low_utilization_threshold)>>10)
- goto notlow;
-
- if (ca->low_utilization_start == 0) {
- ca->low_utilization = 0;
- ca->low_utilization_start = tcp_time_stamp;
- } else if ((s32)(tcp_time_stamp - ca->low_utilization_start)
- > low_utilization_period*HZ) {
- ca->low_utilization = 1;
- }
-
- return;
-
- notlow:
- ca->low_utilization = 0;
- ca->low_utilization_start = 0;
-
-}
-