[CCID2]: Disable broken Ack Ratio adaptation algorithm
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>
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@ -224,8 +224,6 @@ static void ccid2_hc_tx_rto_expire(unsigned long data)
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hctx->ccid2hctx_sent = 0;
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hctx->ccid2hctx_sent = 0;
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/* clear ack ratio state. */
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/* clear ack ratio state. */
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hctx->ccid2hctx_arsent = 0;
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hctx->ccid2hctx_ackloss = 0;
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hctx->ccid2hctx_rpseq = 0;
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hctx->ccid2hctx_rpseq = 0;
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hctx->ccid2hctx_rpdupack = -1;
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hctx->ccid2hctx_rpdupack = -1;
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ccid2_change_l_ack_ratio(sk, 1);
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ccid2_change_l_ack_ratio(sk, 1);
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@ -289,6 +287,26 @@ static void ccid2_hc_tx_packet_sent(struct sock *sk, int more, unsigned int len)
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hctx->ccid2hctx_sent++;
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hctx->ccid2hctx_sent++;
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/*
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* FIXME: The code below is broken and the variables have been removed
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* from the socket struct. The `ackloss' variable was always set to 0,
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* and with arsent there are several problems:
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* (i) it doesn't just count the number of Acks, but all sent packets;
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* (ii) it is expressed in # of packets, not # of windows, so the
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* comparison below uses the wrong formula: Appendix A of RFC 4341
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* comes up with the number K = cwnd / (R^2 - R) of consecutive windows
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* of data with no lost or marked Ack packets. If arsent were the # of
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* consecutive Acks received without loss, then Ack Ratio needs to be
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* decreased by 1 when
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* arsent >= K * cwnd / R = cwnd^2 / (R^3 - R^2)
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* where cwnd / R is the number of Acks received per window of data
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* (cf. RFC 4341, App. A). The problems are that
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* - arsent counts other packets as well;
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* - the comparison uses a formula different from RFC 4341;
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* - computing a cubic/quadratic equation each time is too complicated.
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* Hence a different algorithm is needed.
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*/
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#if 0
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/* Ack Ratio. Need to maintain a concept of how many windows we sent */
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/* Ack Ratio. Need to maintain a concept of how many windows we sent */
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hctx->ccid2hctx_arsent++;
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hctx->ccid2hctx_arsent++;
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/* We had an ack loss in this window... */
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/* We had an ack loss in this window... */
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@ -316,6 +334,7 @@ static void ccid2_hc_tx_packet_sent(struct sock *sk, int more, unsigned int len)
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hctx->ccid2hctx_arsent = 0; /* or maybe set it to cwnd*/
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hctx->ccid2hctx_arsent = 0; /* or maybe set it to cwnd*/
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}
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}
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}
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}
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#endif
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/* setup RTO timer */
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/* setup RTO timer */
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if (!timer_pending(&hctx->ccid2hctx_rtotimer))
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if (!timer_pending(&hctx->ccid2hctx_rtotimer))
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@ -44,8 +44,6 @@ struct ccid2_seq {
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* @ccid2hctx_acks - ACKS recv in AI phase
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* @ccid2hctx_acks - ACKS recv in AI phase
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* @ccid2hctx_sent - packets sent in this window
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* @ccid2hctx_sent - packets sent in this window
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* @ccid2hctx_lastrtt -time RTT was last measured
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* @ccid2hctx_lastrtt -time RTT was last measured
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* @ccid2hctx_arsent - packets sent [ack ratio]
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* @ccid2hctx_ackloss - ack was lost in this win
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* @ccid2hctx_rpseq - last consecutive seqno
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* @ccid2hctx_rpseq - last consecutive seqno
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* @ccid2hctx_rpdupack - dupacks since rpseq
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* @ccid2hctx_rpdupack - dupacks since rpseq
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*/
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*/
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@ -66,8 +64,6 @@ struct ccid2_hc_tx_sock {
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int ccid2hctx_sent;
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int ccid2hctx_sent;
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unsigned long ccid2hctx_lastrtt;
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unsigned long ccid2hctx_lastrtt;
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struct timer_list ccid2hctx_rtotimer;
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struct timer_list ccid2hctx_rtotimer;
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unsigned long ccid2hctx_arsent;
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int ccid2hctx_ackloss;
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u64 ccid2hctx_rpseq;
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u64 ccid2hctx_rpseq;
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int ccid2hctx_rpdupack;
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int ccid2hctx_rpdupack;
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int ccid2hctx_sendwait;
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int ccid2hctx_sendwait;
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