[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 d7b688e..df88c54b 100644
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -103,13 +103,7 @@
/* 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 @@
"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,