1 files changed, 30 insertions, 0 deletions

diff --git a/net/dccp/ccids/lib/packet_history.c b/net/dccp/ccids/lib/packet_history.c
index 5c4ded1cf42..547ad098ea6 100644
--- a/net/dccp/ccids/lib/packet_history.c
+++ b/net/dccp/ccids/lib/packet_history.c
@@ -385,6 +385,36 @@ int tfrc_rx_handle_loss(struct tfrc_rx_hist *h,
 }
 EXPORT_SYMBOL_GPL(tfrc_rx_handle_loss);
 
+/* Compute the sending rate X_recv measured between feedback intervals */
+u32 tfrc_rx_hist_x_recv(struct tfrc_rx_hist *h, const u32 last_x_recv)
+{
+        u64 bytes = h->bytes_recvd, last_rtt = h->rtt_estimate;
+        s64 delta = ktime_to_us(net_timedelta(h->bytes_start));
+
+        WARN_ON(delta <= 0);
+        /*
+         * Ensure that the sampling interval for X_recv is at least one RTT,
+         * by extending the sampling interval backwards in time, over the last
+         * R_(m-1) seconds, as per rfc3448bis-06, 6.2.
+         * To reduce noise (e.g. when the RTT changes often), this is only
+         * done when delta is smaller than RTT/2.
+         */
+        if (last_x_recv > 0 && delta < last_rtt/2) {
+                tfrc_pr_debug("delta < RTT ==> %ld us < %u us\n",
+                              (long)delta, (unsigned)last_rtt);
+
+                delta = (bytes ? delta : 0) + last_rtt;
+                bytes += div_u64((u64)last_x_recv * last_rtt, USEC_PER_SEC);
+        }
+
+        if (unlikely(bytes == 0)) {
+                DCCP_WARN("X_recv == 0, using old value of %u\n", last_x_recv);
+                return last_x_recv;
+        }
+        return scaled_div32(bytes, delta);
+}
+EXPORT_SYMBOL_GPL(tfrc_rx_hist_x_recv);
+
 void tfrc_rx_hist_purge(struct tfrc_rx_hist *h)
 {
         int i;