[IPV4]: fib_trie root-node expansion
The patch below introduces special thresholds to keep root node in the trie
large. This gives a flatter tree at the cost of a modest memory increase.
Overall it seems to be gain and this was also proposed by one the authors
of the paper in recent a seminar.
Main table after loading 123 k routes.
Aver depth: 3.30
Max depth: 9
Root-node size 12 bits
Total size: 4044 kB
With the patch:
Aver depth: 2.78
Max depth: 8
Root-node size 15 bits
Total size: 4150 kB
An increase of 8-10% was seen in forwading performance for an rDoS attack.
Signed-off-by: Robert Olsson <robert.olsson@its.uu.se>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
index 50c0519..0093ea0 100644
--- a/net/ipv4/fib_trie.c
+++ b/net/ipv4/fib_trie.c
@@ -286,6 +286,8 @@
static int halve_threshold = 25;
static int inflate_threshold = 50;
+static int halve_threshold_root = 15;
+static int inflate_threshold_root = 25;
static void __alias_free_mem(struct rcu_head *head)
@@ -449,6 +451,8 @@
int i;
int err = 0;
struct tnode *old_tn;
+ int inflate_threshold_use;
+ int halve_threshold_use;
if (!tn)
return NULL;
@@ -541,10 +545,17 @@
check_tnode(tn);
+ /* Keep root node larger */
+
+ if(!tn->parent)
+ inflate_threshold_use = inflate_threshold_root;
+ else
+ inflate_threshold_use = inflate_threshold;
+
err = 0;
while ((tn->full_children > 0 &&
50 * (tn->full_children + tnode_child_length(tn) - tn->empty_children) >=
- inflate_threshold * tnode_child_length(tn))) {
+ inflate_threshold_use * tnode_child_length(tn))) {
old_tn = tn;
tn = inflate(t, tn);
@@ -564,10 +575,18 @@
* node is above threshold.
*/
+
+ /* Keep root node larger */
+
+ if(!tn->parent)
+ halve_threshold_use = halve_threshold_root;
+ else
+ halve_threshold_use = halve_threshold;
+
err = 0;
while (tn->bits > 1 &&
100 * (tnode_child_length(tn) - tn->empty_children) <
- halve_threshold * tnode_child_length(tn)) {
+ halve_threshold_use * tnode_child_length(tn)) {
old_tn = tn;
tn = halve(t, tn);