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[CCID2]: Disable broken Ack Ratio adaptation algorithm

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This comments out a problematic section comprising a half-finished algorithm:

 - The variable `ccid2hctx_ackloss' is never initialised to a value different from 0 and
   hence in fact is a read-only constant.
 - The `arsent' variable counts packets other than Acks (it is incremented for every packet),
   and there is no test for Ack Loss.
 - The concept of counting Acks as such leads to a complex calculation, and the calculation
   at the moment is inconsistent with this concept.
   The problem is that the number of Acks - rather than the number of windows - is counted,
   which leads to a complex (cubic/quadratic) expression - this is not even implemented.

In its current state, the commented-out algorithm interfers with normal processing by
changing Ack Ratio incorrectly, and at the wrong times.

A new algorithm is necessary, which will not necessarily use the same variables as used by
the unfinished one; hence the old variables have been removed.

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@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Gerrit Renker 2007-11-24 21:58:33 -02:00 committed by David S. Miller
parent b00d2bbc45
commit 900bfed471
2 changed files with 21 additions and 6 deletions
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23
net/dccp/ccids/ccid2.c
View File

@ -224,8 +224,6 @@ static void ccid2_hc_tx_rto_expire(unsigned long data)
hctx->ccid2hctx_sent = 0;
/* clear ack ratio state. */
hctx->ccid2hctx_arsent = 0;
hctx->ccid2hctx_ackloss = 0;
hctx->ccid2hctx_rpseq = 0;
hctx->ccid2hctx_rpdupack = -1;
ccid2_change_l_ack_ratio(sk, 1);
@ -289,6 +287,26 @@ static void ccid2_hc_tx_packet_sent(struct sock *sk, int more, unsigned int len)
hctx->ccid2hctx_sent++;
/*
* FIXME: The code below is broken and the variables have been removed
* from the socket struct. The `ackloss' variable was always set to 0,
* and with arsent there are several problems:
* (i) it doesn't just count the number of Acks, but all sent packets;
* (ii) it is expressed in # of packets, not # of windows, so the
* comparison below uses the wrong formula: Appendix A of RFC 4341
* comes up with the number K = cwnd / (R^2 - R) of consecutive windows
* of data with no lost or marked Ack packets. If arsent were the # of
* consecutive Acks received without loss, then Ack Ratio needs to be
* decreased by 1 when
* arsent >= K * cwnd / R = cwnd^2 / (R^3 - R^2)
* where cwnd / R is the number of Acks received per window of data
* (cf. RFC 4341, App. A). The problems are that
* - arsent counts other packets as well;
* - the comparison uses a formula different from RFC 4341;
* - computing a cubic/quadratic equation each time is too complicated.
* Hence a different algorithm is needed.
*/
#if 0
/* Ack Ratio. Need to maintain a concept of how many windows we sent */
hctx->ccid2hctx_arsent++;
/* We had an ack loss in this window... */
@ -316,6 +334,7 @@ static void ccid2_hc_tx_packet_sent(struct sock *sk, int more, unsigned int len)
hctx->ccid2hctx_arsent = 0; /* or maybe set it to cwnd*/
}
}
#endif
/* setup RTO timer */
if (!timer_pending(&hctx->ccid2hctx_rtotimer))

4
net/dccp/ccids/ccid2.h
View File

@ -44,8 +44,6 @@ struct ccid2_seq {
* @ccid2hctx_acks - ACKS recv in AI phase
* @ccid2hctx_sent - packets sent in this window
* @ccid2hctx_lastrtt -time RTT was last measured
* @ccid2hctx_arsent - packets sent [ack ratio]
* @ccid2hctx_ackloss - ack was lost in this win
* @ccid2hctx_rpseq - last consecutive seqno
* @ccid2hctx_rpdupack - dupacks since rpseq
*/
@ -66,8 +64,6 @@ struct ccid2_hc_tx_sock {
int ccid2hctx_sent;
unsigned long ccid2hctx_lastrtt;
struct timer_list ccid2hctx_rtotimer;
unsigned long ccid2hctx_arsent;
int ccid2hctx_ackloss;
u64 ccid2hctx_rpseq;
int ccid2hctx_rpdupack;
int ccid2hctx_sendwait;