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authorGerrit Renker <gerrit@erg.abdn.ac.uk>2007-11-24 21:58:33 -0200
committerDavid S. Miller <davem@davemloft.net>2008-01-28 14:54:55 -0800
commit900bfed4718126e6c32244903b6f43e0990d04ad (patch)
treed4644ea4770657046d762d9997d7a8e1d794ff94
parentb00d2bbc45a287c9a72374582ce42205f3412419 (diff)
[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>
-rw-r--r--net/dccp/ccids/ccid2.c23
-rw-r--r--net/dccp/ccids/ccid2.h4
2 files changed, 21 insertions, 6 deletions
diff --git a/net/dccp/ccids/ccid2.c b/net/dccp/ccids/ccid2.c
index 9c5b6c73f7c..a901202ada6 100644
--- a/net/dccp/ccids/ccid2.c
+++ b/net/dccp/ccids/ccid2.c
@@ -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))
diff --git a/net/dccp/ccids/ccid2.h b/net/dccp/ccids/ccid2.h
index d9daa534c9b..ed95f8f0cc4 100644
--- a/net/dccp/ccids/ccid2.h
+++ b/net/dccp/ccids/ccid2.h
@@ -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;