/** * tfrc_rx_hist_sample_rtt - Sample RTT from timestamp / CCVal * Based on ideas presented in RFC 4342, 8.1. Returns 0 if it was not able * to compute a sample with given data - calling function should check this. */ u32 tfrc_rx_hist_sample_rtt(struct tfrc_rx_hist *h, const struct sk_buff *skb) { u32 sample = 0, delta_v = SUB16(dccp_hdr(skb)->dccph_ccval, tfrc_rx_hist_rtt_last_s(h)->tfrchrx_ccval); if (delta_v < 1 || delta_v > 4) { /* unsuitable CCVal delta */ if (h->rtt_sample_prev == 2) { /* previous candidate stored */ sample = SUB16(tfrc_rx_hist_rtt_prev_s(h)->tfrchrx_ccval, tfrc_rx_hist_rtt_last_s(h)->tfrchrx_ccval); if (sample) sample = 4 / sample * ktime_us_delta(tfrc_rx_hist_rtt_prev_s(h)->tfrchrx_tstamp, tfrc_rx_hist_rtt_last_s(h)->tfrchrx_tstamp); else /* * FIXME: This condition is in principle not * possible but occurs when CCID is used for * two-way data traffic. I have tried to trace * it, but the cause does not seem to be here. */ DCCP_BUG("please report to [email protected]" " => prev = %u, last = %u", tfrc_rx_hist_rtt_prev_s(h)->tfrchrx_ccval, tfrc_rx_hist_rtt_last_s(h)->tfrchrx_ccval); } else if (delta_v < 1) { h->rtt_sample_prev = 1; goto keep_ref_for_next_time; } } else if (delta_v == 4) /* optimal match */ sample = ktime_to_us(net_timedelta(tfrc_rx_hist_rtt_last_s(h)->tfrchrx_tstamp)); else { /* suboptimal match */ h->rtt_sample_prev = 2; goto keep_ref_for_next_time; } if (unlikely(sample > DCCP_SANE_RTT_MAX)) { DCCP_WARN("RTT sample %u too large, using max\n", sample); sample = DCCP_SANE_RTT_MAX; } h->rtt_sample_prev = 0; /* use current entry as next reference */ keep_ref_for_next_time: return sample; }
u32 tfrc_rx_hist_sample_rtt(struct tfrc_rx_hist *h, const struct sk_buff *skb) { u32 sample = 0, delta_v = SUB16(dccp_hdr(skb)->dccph_ccval, tfrc_rx_hist_rtt_last_s(h)->tfrchrx_ccval); if (delta_v < 1 || delta_v > 4) { /* */ if (h->rtt_sample_prev == 2) { /* */ sample = SUB16(tfrc_rx_hist_rtt_prev_s(h)->tfrchrx_ccval, tfrc_rx_hist_rtt_last_s(h)->tfrchrx_ccval); if (sample) sample = 4 / sample * ktime_us_delta(tfrc_rx_hist_rtt_prev_s(h)->tfrchrx_tstamp, tfrc_rx_hist_rtt_last_s(h)->tfrchrx_tstamp); else /* */ DCCP_BUG("please report to [email protected]" " => prev = %u, last = %u", tfrc_rx_hist_rtt_prev_s(h)->tfrchrx_ccval, tfrc_rx_hist_rtt_last_s(h)->tfrchrx_ccval); } else if (delta_v < 1) { h->rtt_sample_prev = 1; goto keep_ref_for_next_time; } } else if (delta_v == 4) /* */ sample = ktime_to_us(net_timedelta(tfrc_rx_hist_rtt_last_s(h)->tfrchrx_tstamp)); else { /* */ h->rtt_sample_prev = 2; goto keep_ref_for_next_time; } if (unlikely(sample > DCCP_SANE_RTT_MAX)) { DCCP_WARN("RTT sample %u too large, using max\n", sample); sample = DCCP_SANE_RTT_MAX; } h->rtt_sample_prev = 0; /* */ keep_ref_for_next_time: return sample; }