[DCCP]: Fix CCID3

This fixes CCID3 to give much closer performance to RFC4342.

CCID3 is meant to alter sending rate based on RTT and loss.

The performance was verified against:
http://wand.net.nz/~perry/max_download.php

For example I tested with netem and had the following parameters:
Delayed Acks 1, MSS 256 bytes, RTT 105 ms, packet loss 5%.

This gives a theoretical speed of 71.9 Kbits/s. I measured across three
runs with this patch set and got 70.1 Kbits/s. Without this patchset the
average was 232 Kbits/s which means Linux can't be used for CCID3 research
properly.

I also tested with netem turned off so box just acting as router with 1.2
msec RTT. The performance with this is the same with or without the patch
at around 30 Mbit/s.

Signed off by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 17 insertions, 17 deletions

diff --git a/net/dccp/ccids/lib/loss_interval.c b/net/dccp/ccids/lib/loss_interval.c
index b93d9fc98cb..906c81ab9d4 100644
--- a/net/dccp/ccids/lib/loss_interval.c
+++ b/net/dccp/ccids/lib/loss_interval.c
@@ -12,6 +12,7 @@
  */
 
 #include <linux/module.h>
+#include <net/sock.h>
 
 #include "loss_interval.h"
 
@@ -90,13 +91,13 @@ u32 dccp_li_hist_calc_i_mean(struct list_head *list)
 	u32 w_tot  = 0;
 
 	list_for_each_entry_safe(li_entry, li_next, list, dccplih_node) {
-		if (i < DCCP_LI_HIST_IVAL_F_LENGTH) {
+		if (li_entry->dccplih_interval != ~0) {
 			i_tot0 += li_entry->dccplih_interval * dccp_li_hist_w[i];
 			w_tot  += dccp_li_hist_w[i];
+			if (i != 0)
+				i_tot1 += li_entry->dccplih_interval * dccp_li_hist_w[i - 1];
 		}
 
-		if (i != 0)
-			i_tot1 += li_entry->dccplih_interval * dccp_li_hist_w[i - 1];
 
 		if (++i > DCCP_LI_HIST_IVAL_F_LENGTH)
 			break;
@@ -107,37 +108,36 @@ u32 dccp_li_hist_calc_i_mean(struct list_head *list)
 
 	i_tot = max(i_tot0, i_tot1);
 
-	/* FIXME: Why do we do this? -Ian McDonald */
-	if (i_tot * 4 < w_tot)
-		i_tot = w_tot * 4;
+	if (!w_tot) {
+		LIMIT_NETDEBUG(KERN_WARNING "%s: w_tot = 0\n", __FUNCTION__);
+		return 1;
+	}
 
-	return i_tot * 4 / w_tot;
+	return i_tot / w_tot;
 }
 
 EXPORT_SYMBOL_GPL(dccp_li_hist_calc_i_mean);
 
-struct dccp_li_hist_entry *dccp_li_hist_interval_new(struct dccp_li_hist *hist,
-						     struct list_head *list,
-						     const u64 seq_loss,
-						     const u8 win_loss)
+int dccp_li_hist_interval_new(struct dccp_li_hist *hist,
+   struct list_head *list, const u64 seq_loss, const u8 win_loss)
 {
-	struct dccp_li_hist_entry *tail = NULL, *entry;
+	struct dccp_li_hist_entry *entry;
 	int i;
 
-	for (i = 0; i <= DCCP_LI_HIST_IVAL_F_LENGTH; ++i) {
+	for (i = 0; i < DCCP_LI_HIST_IVAL_F_LENGTH; i++) {
 		entry = dccp_li_hist_entry_new(hist, SLAB_ATOMIC);
 		if (entry == NULL) {
 			dccp_li_hist_purge(hist, list);
-			return NULL;
+			dump_stack();
+			return 0;
 		}
-		if (tail == NULL)
-			tail = entry;
+		entry->dccplih_interval = ~0;
 		list_add(&entry->dccplih_node, list);
 	}
 
 	entry->dccplih_seqno     = seq_loss;
 	entry->dccplih_win_count = win_loss;
-	return tail;
+	return 1;
 }
 
 EXPORT_SYMBOL_GPL(dccp_li_hist_interval_new);