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[IPV4]: fib_trie root-node expansion

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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>
This commit is contained in:
Robert Olsson 2005-10-04 13:01:58 -07:00 committed by David S. Miller
parent 87bf9c97b4
commit e6308be85a
1 changed files with 21 additions and 2 deletions
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23
net/ipv4/fib_trie.c
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@ -286,6 +286,8 @@ static inline void check_tnode(const struct tnode *tn)
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 @@ static struct node *resize(struct trie *t, struct tnode *tn)
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 @@ static struct node *resize(struct trie *t, struct tnode *tn)
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 @@ static struct node *resize(struct trie *t, struct tnode *tn)
* 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);