1 files changed, 24 insertions, 59 deletions

diff --git a/net/dccp/ccids/lib/packet_history.c b/net/dccp/ccids/lib/packet_history.c
index e2e250aa5c89..5c4ded1cf422 100644
--- a/net/dccp/ccids/lib/packet_history.c
+++ b/net/dccp/ccids/lib/packet_history.c
@@ -428,31 +428,16 @@ int tfrc_rx_hist_init(struct tfrc_rx_hist *h, struct sock *sk)
 EXPORT_SYMBOL_GPL(tfrc_rx_hist_init);
 
 /**
- * tfrc_rx_hist_rtt_last_s - reference entry to compute RTT samples against
- */
-static inline struct tfrc_rx_hist_entry *
-                        tfrc_rx_hist_rtt_last_s(const struct tfrc_rx_hist *h)
-{
-        return h->ring[0];
-}
-
-/**
- * tfrc_rx_hist_rtt_prev_s: previously suitable (wrt rtt_last_s) RTT-sampling entry
- */
-static inline struct tfrc_rx_hist_entry *
-                        tfrc_rx_hist_rtt_prev_s(const struct tfrc_rx_hist *h)
-{
-        return h->ring[h->rtt_sample_prev];
-}
-
-/**
  * 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.
+ * Based on ideas presented in RFC 4342, 8.1. This function expects that no loss
+ * is pending and uses the following history entries (via rtt_sample_prev):
+ * - h->ring[0]  contains the most recent history entry prior to @skb;
+ * - h->ring[1]  is an unused `dummy' entry when the current difference is 0;
  */
 void tfrc_rx_hist_sample_rtt(struct tfrc_rx_hist *h, const struct sk_buff *skb)
 {
-        u32 sample = 0, delta_v;
+        struct tfrc_rx_hist_entry *last = h->ring[0];
+        u32 sample, delta_v;
 
         /*
          * When not to sample:
@@ -466,47 +451,27 @@ void tfrc_rx_hist_sample_rtt(struct tfrc_rx_hist *h, const struct sk_buff *skb)
             tfrc_rx_hist_loss_pending(h))
                 return;
 
-        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 dccp@vger.kernel.org"
-                                         " => 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;
-        }
+        h->rtt_sample_prev = 0;         /* reset previous candidate */
 
-        if (unlikely(sample > DCCP_SANE_RTT_MAX)) {
-                DCCP_WARN("RTT sample %u too large, using max\n", sample);
-                sample = DCCP_SANE_RTT_MAX;
+        delta_v = SUB16(dccp_hdr(skb)->dccph_ccval, last->tfrchrx_ccval);
+        if (delta_v == 0) {             /* less than RTT/4 difference */
+                h->rtt_sample_prev = 1;
+                return;
         }
+        sample = dccp_sane_rtt(ktime_to_us(net_timedelta(last->tfrchrx_tstamp)));
 
-        h->rtt_sample_prev = 0;        /* use current entry as next reference */
-keep_ref_for_next_time:
+        if (delta_v <= 4)               /* between RTT/4 and RTT */
+                sample *= 4 / delta_v;
+        else if (!(sample < h->rtt_estimate && sample > h->rtt_estimate/2))
+                /*
+                * Optimisation: CCVal difference is greater than 1 RTT, yet the
+                * sample is less than the local RTT estimate; which means that
+                * the RTT estimate is too high.
+                * To avoid noise, it is not done if the sample is below RTT/2.
+                */
+                return;
 
-        h->rtt_estimate = tfrc_ewma(h->rtt_estimate, sample, 9);
+        /* Use a lower weight than usual to increase responsiveness */
+        h->rtt_estimate = tfrc_ewma(h->rtt_estimate, sample, 5);
 }
 EXPORT_SYMBOL_GPL(tfrc_rx_hist_sample_rtt);