[CCID3]: Inline for moving average

The moving average computation occurs so frequently in the CCID 3 code that
it merits an inline function  of its own. This is uses a suggestion by
Arnaldo as per http://www.mail-archive.com/dccp@vger.kernel.org/msg01662.html

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 14 insertions, 20 deletions

diff --git a/net/dccp/ccids/ccid3.c b/net/dccp/ccids/ccid3.c
index 94a322863844..42893b1dfa09 100644
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -192,7 +192,7 @@ static inline void ccid3_hc_tx_update_s(struct ccid3_hc_tx_sock *hctx, int len)
 {
         const u16 old_s = hctx->ccid3hctx_s;
 
-        hctx->ccid3hctx_s = old_s == 0 ? len : (9 * old_s + len) / 10;
+        hctx->ccid3hctx_s = tfrc_ewma(hctx->ccid3hctx_s, len, 9);
 
         if (hctx->ccid3hctx_s != old_s)
                 ccid3_update_send_interval(hctx);
@@ -449,25 +449,15 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
 
                 now = ktime_get_real();
                 /*
-                 * Calculate new round trip sample as per [RFC 3448, 4.3] by
-                 *      R_sample  =  (now - t_recvdata) - t_elapsed
+                 * Calculate new RTT sample and update moving average
                  */
                 r_sample = dccp_sample_rtt(sk, ktime_us_delta(now, packet->dccphtx_tstamp));
+                hctx->ccid3hctx_rtt = tfrc_ewma(hctx->ccid3hctx_rtt, r_sample, 9);
 
-                /*
-                 * Update RTT estimate by
-                 * If (No feedback recv)
-                 *    R = R_sample;
-                 * Else
-                 *    R = q * R + (1 - q) * R_sample;
-                 *
-                 * q is a constant, RFC 3448 recomments 0.9
-                 */
                 if (hctx->ccid3hctx_state == TFRC_SSTATE_NO_FBACK) {
                         /*
                          * Larger Initial Windows [RFC 4342, sec. 5]
                          */
-                        hctx->ccid3hctx_rtt  = r_sample;
                         hctx->ccid3hctx_x    = rfc3390_initial_rate(sk);
                         hctx->ccid3hctx_t_ld = now;
 
@@ -481,8 +471,6 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
 
                         ccid3_hc_tx_set_state(sk, TFRC_SSTATE_FBACK);
                 } else {
-                        hctx->ccid3hctx_rtt = (9 * hctx->ccid3hctx_rtt +
-                                                   r_sample) / 10;
 
                         /* Update sending rate (step 4 of [RFC 3448, 4.3]) */
                         if (hctx->ccid3hctx_p > 0)
@@ -700,11 +688,8 @@ static void ccid3_hc_rx_set_state(struct sock *sk,
 
 static inline void ccid3_hc_rx_update_s(struct ccid3_hc_rx_sock *hcrx, int len)
 {
-        if (unlikely(len == 0)) /* don't update on empty packets (e.g. ACKs) */
-                ccid3_pr_debug("Packet payload length is 0 - not updating\n");
-        else
-                hcrx->ccid3hcrx_s = hcrx->ccid3hcrx_s == 0 ? len :
-                                    (9 * hcrx->ccid3hcrx_s + len) / 10;
+        if (likely(len > 0))    /* don't update on empty packets (e.g. ACKs) */
+                hcrx->ccid3hcrx_s = tfrc_ewma(hcrx->ccid3hcrx_s, len, 9);
 }
 
 static void ccid3_hc_rx_send_feedback(struct sock *sk)
diff --git a/net/dccp/ccids/lib/tfrc.h b/net/dccp/ccids/lib/tfrc.h
index faf5f7e219e3..5a0ba86df183 100644
--- a/net/dccp/ccids/lib/tfrc.h
+++ b/net/dccp/ccids/lib/tfrc.h
@@ -37,6 +37,15 @@ static inline u32 scaled_div32(u64 a, u32 b)
         return result;
 }
 
+/**
+ * tfrc_ewma  -  Exponentially weighted moving average
+ * @weight: Weight to be used as damping factor, in units of 1/10
+ */
+static inline u32 tfrc_ewma(const u32 avg, const u32 newval, const u8 weight)
+{
+        return avg ? (weight * avg + (10 - weight) * newval) / 10 : newval;
+}
+
 extern u32 tfrc_calc_x(u16 s, u32 R, u32 p);
 extern u32 tfrc_calc_x_reverse_lookup(u32 fvalue);