3 files changed, 19 insertions, 21 deletions

diff --git a/include/net/tcp.h b/include/net/tcp.h
index df6a2eb20193..a64022199b62 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -779,6 +779,21 @@ static inline __u32 tcp_current_ssthresh(const struct sock *sk)
 /* Use define here intentionally to get WARN_ON location shown at the caller */
 #define tcp_verify_left_out(tp) WARN_ON(tcp_left_out(tp) > tp->packets_out)
 
+/*
+ * Convert RFC 3390 larger initial window into an equivalent number of packets.
+ *
+ * John Heffner states:
+ *
+ *      The RFC specifies a window of no more than 4380 bytes
+ *      unless 2*MSS > 4380.  Reading the pseudocode in the RFC
+ *      is a bit misleading because they use a clamp at 4380 bytes
+ *      rather than a multiplier in the relevant range.
+ */
+static inline u32 rfc3390_bytes_to_packets(const u32 smss)
+{
+        return smss <= 1095 ? 4 : (smss > 1460 ? 2 : 3);
+}
+
 extern void tcp_enter_cwr(struct sock *sk, const int set_ssthresh);
 extern __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst);
 
diff --git a/net/dccp/ccids/ccid2.c b/net/dccp/ccids/ccid2.c
index 8c95813bcc67..b9c942a09c98 100644
--- a/net/dccp/ccids/ccid2.c
+++ b/net/dccp/ccids/ccid2.c
@@ -641,12 +641,8 @@ static int ccid2_hc_tx_init(struct ccid *ccid, struct sock *sk)
         /* RFC 4341, 5: initialise ssthresh to arbitrarily high (max) value */
         hc->tx_ssthresh = ~0U;
 
-        /*
-         * RFC 4341, 5: "The cwnd parameter is initialized to at most four
-         * packets for new connections, following the rules from [RFC3390]".
-         * We need to convert the bytes of RFC3390 into the packets of RFC 4341.
-         */
-        hc->tx_cwnd = clamp(4380U / dp->dccps_mss_cache, 2U, 4U);
+        /* Use larger initial windows (RFC 4341, section 5). */
+        hc->tx_cwnd = rfc3390_bytes_to_packets(dp->dccps_mss_cache);
 
         /* Make sure that Ack Ratio is enabled and within bounds. */
         max_ratio = DIV_ROUND_UP(hc->tx_cwnd, 2);
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index e663b78a2ef6..1bc87a05c734 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -805,25 +805,12 @@ void tcp_update_metrics(struct sock *sk)
         }
 }
 
-/* Numbers are taken from RFC3390.
- *
- * John Heffner states:
- *
- *      The RFC specifies a window of no more than 4380 bytes
- *      unless 2*MSS > 4380.  Reading the pseudocode in the RFC
- *      is a bit misleading because they use a clamp at 4380 bytes
- *      rather than use a multiplier in the relevant range.
- */
 __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst)
 {
         __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
 
-        if (!cwnd) {
-                if (tp->mss_cache > 1460)
-                        cwnd = 2;
-                else
-                        cwnd = (tp->mss_cache > 1095) ? 3 : 4;
-        }
+        if (!cwnd)
+                cwnd = rfc3390_bytes_to_packets(tp->mss_cache);
         return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
 }