[DCCP] ccid3: Simplify control flow in the calculation of t_ipi

This patch performs a simplifying (performance) optimisation:

 In each call of the inline function ccid3_calc_new_t_ipi(), the state is
 tested against TFRC_SSTATE_NO_FBACK. This is expensive when the function
 is called very often. A simpler solution, implemented by this patch, is
 to adapt the control flow.

Background:

diff --git a/net/dccp/ccids/ccid3.c b/net/dccp/ccids/ccid3.c
index d7b688e9f983c997486d19268261348ec5adfa2a..df88c54b2ec5d0bd81274abc6b8c3f7f3522292f 100644 (file)
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -103,13 +103,7 @@ static void ccid3_hc_tx_set_state(struct sock *sk,
 /* Calculate new t_ipi (inter packet interval) by t_ipi = s / X_inst */
 static inline void ccid3_calc_new_t_ipi(struct ccid3_hc_tx_sock *hctx)
 {
-       /*
-        * If no feedback spec says t_ipi is 1 second (set elsewhere and then
-        * doubles after every no feedback timer (separate function)
-        */
-       if (hctx->ccid3hctx_state != TFRC_SSTATE_NO_FBACK)
-               hctx->ccid3hctx_t_ipi = usecs_div(hctx->ccid3hctx_s,
-                                                 hctx->ccid3hctx_x);
+       hctx->ccid3hctx_t_ipi = usecs_div(hctx->ccid3hctx_s, hctx->ccid3hctx_x);
 }
 
 /* Calculate new delta by delta = min(t_ipi / 2, t_gran / 2) */
@@ -395,6 +389,8 @@ static void ccid3_hc_tx_packet_sent(struct sock *sk, int more, int len)
                                  "as a data packet",  dccp_role(sk));
                return;
        case TFRC_SSTATE_NO_FBACK:
+               /* t_nom, t_ipi, delta do not change until feedback arrives */
+               return;
        case TFRC_SSTATE_FBACK:
                if (len > 0) {
                        timeval_sub_usecs(&hctx->ccid3hctx_t_nom,