[CCID 3]: 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:
-----------
Upon sender initialisation, the values of t_ipi, t_nom = t_0, delta, as
well as the initial packet sending rate, are all constants [RFC 3448, 4.2].
Until feedback arrives, these values are not changed. Hence it is not necessary
to recalculate t_ipi, t_nom, delta until the first feedback has arrived, i.e.
as long as the state TFRC_SSTATE_NO_FBACK persists.
Justification:
--------------
ccid3_calc_new_t_ipi() is called only in two places:
* in ccid3_hc_tx_packet_recv(); here the state is never TFRC_SSTATE_NO_FBACK, due to
if (hctx->ccid3hctx_state == TFRC_SSTATE_NO_FBACK) {
ccid3_hc_tx_set_state(sk, TFRC_SSTATE_FBACK);
/* ... */
* in ccid3_hc_tx_packet_sent()
==> Only in the second case, the state might be TFRC_SSTATE_NO_FBACK and this only
during the initial phase of a connection.
Solution:
---------
This patch avoids such a recalculation by a simple change of control flow in
ccid3_hc_tx_packet_sent(). As a consequence, ccid3_calc_new_t_ipi() is never called in
the state TFRC_SSTATE_NO_FBACK, hence the test against this state can safely be removed.
In addition, a problematic comment in ccid3_calc_new_t_ipi() was removed:
* the first part of the comment (initial t_ipi = 1 second) is correct
* the second part of the comment is not correct wrt. [RFC 3448, 4.4]
Signed-off-by: Gerrit Renker <gerrit@xxxxxxxxxxxxxx>
---
net/dccp/ccids/ccid3.c | 2 ++
1 file changed, 2 insertions(+)
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -103,13 +103,7 @@ static void ccid3_hc_tx_set_state(struct
/* 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) */
@@ -394,6 +388,8 @@ static void ccid3_hc_tx_packet_sent(stru
"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,
-
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