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[DCCP] ccid3: Shift window counter computation

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This puts the window counter computation [RFC 4342, 8.1] into a separate
 function which is called whenever a new packet is ready for immediate
 transmission in ccid3_hc_tx_send_packet.

Justification:

 The window counter update was previously computed after the packet was sent. This has
 two drawbacks, both fixed by this patch:
   1) re-compute another timestamp almost directly after the packet was sent (expensive),
   2) the CCVal for the window counter is needed at the instant the packet is sent.

Further details:

 The initialisation of the window counter is left in the state NO_SENT, as before.
 The algorithm will do nothing if either RTT is initialised to 0 (which is ok) or if
 the RTT value remains below 4 microseconds (which is almost pathological).

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
This commit is contained in:
Gerrit Renker 2006-12-10 00:07:37 -02:00 committed by David S. Miller
parent de553c189e
commit 9f8681db96
1 changed files with 29 additions and 20 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

49
net/dccp/ccids/ccid3.c
View file

@ -161,6 +161,33 @@ static inline void ccid3_hc_tx_update_s(struct ccid3_hc_tx_sock *hctx, int len)
*/
}
/*
* Update Window Counter using the algorithm from [RFC 4342, 8.1].
* The algorithm is not applicable if RTT < 4 microseconds.
*/
static inline void ccid3_hc_tx_update_win_count(struct ccid3_hc_tx_sock *hctx,
struct timeval *now)
{
suseconds_t delta;
u32 quarter_rtts;
if (unlikely(hctx->ccid3hctx_rtt < 4)) /* avoid divide-by-zero */
return;
delta = timeval_delta(now, &hctx->ccid3hctx_t_last_win_count);
DCCP_BUG_ON(delta < 0);
quarter_rtts = (u32)delta / (hctx->ccid3hctx_rtt / 4);
if (quarter_rtts > 0) {
hctx->ccid3hctx_t_last_win_count = *now;
hctx->ccid3hctx_last_win_count += min_t(u32, quarter_rtts, 5);
hctx->ccid3hctx_last_win_count &= 0xF; /* mod 16 */
ccid3_pr_debug("now at %#X\n", hctx->ccid3hctx_last_win_count);
}
}
static void ccid3_hc_tx_no_feedback_timer(unsigned long data)
{
struct sock *sk = (struct sock *)data;
@ -333,6 +360,8 @@ static int ccid3_hc_tx_send_packet(struct sock *sk, struct sk_buff *skb)
*/
if (delay - (suseconds_t)hctx->ccid3hctx_delta >= 0)
return delay / 1000L;
ccid3_hc_tx_update_win_count(hctx, &now);
break;
case TFRC_SSTATE_TERM:
DCCP_BUG("Illegal %s state TERM, sk=%p", dccp_role(sk), sk);
@ -353,7 +382,6 @@ static void ccid3_hc_tx_packet_sent(struct sock *sk, int more, unsigned int len)
const struct dccp_sock *dp = dccp_sk(sk);
struct ccid3_hc_tx_sock *hctx = ccid3_hc_tx_sk(sk);
struct timeval now;
suseconds_t quarter_rtt;
struct dccp_tx_hist_entry *packet;
BUG_ON(hctx == NULL);
@ -373,25 +401,6 @@ static void ccid3_hc_tx_packet_sent(struct sock *sk, int more, unsigned int len)
}
packet->dccphtx_tstamp = now;
packet->dccphtx_seqno = dp->dccps_gss;
/*
* Check if win_count have changed
* Algorithm in "8.1. Window Counter Value" in RFC 4342.
*/
quarter_rtt = timeval_delta(&now, &hctx->ccid3hctx_t_last_win_count);
if (likely(hctx->ccid3hctx_rtt > 8))
quarter_rtt /= hctx->ccid3hctx_rtt / 4;
if (quarter_rtt > 0) {
hctx->ccid3hctx_t_last_win_count = now;
hctx->ccid3hctx_last_win_count = (hctx->ccid3hctx_last_win_count +
min_t(unsigned long, quarter_rtt, 5)) % 16;
ccid3_pr_debug("%s, sk=%p, window changed from "
"%u to %u!\n",
dccp_role(sk), sk,
packet->dccphtx_ccval,
hctx->ccid3hctx_last_win_count);
}
hctx->ccid3hctx_idle = 0;
packet->dccphtx_rtt = hctx->ccid3hctx_rtt;
packet->dccphtx_sent = 1;