From bbe34cf8a1a2cc174e6516fc230b91b531da7ddf Mon Sep 17 00:00:00 2001 From: "baker.zhang" Date: Tue, 1 Oct 2013 07:45:09 +0800 Subject: [PATCH] fib_trie: avoid a redundant bit judgement in inflate Because 'node' is the i'st child of 'oldnode', thus, here 'i' equals tkey_extract_bits(node->key, oldtnode->pos, oldtnode->bits) we just get 1 more bit, and need not care the detail value of this bits. I apologize for the mistake. I generated the patch on a branch version, and did not notice the put_child has been changed. I have redone the test on HEAD version with my patch. two cases are used. case 1. inflate a node which has a leaf child node. case 2: inflate a node which has a an child node with skipped bits test env: ip link set eth0 up ip a add dev eth0 192.168.11.1/32 here, we just focus on route table(MAIN), so I use a "192.168.11.1/32" address to simplify the test case. call trace: + fib_insert_node + + trie_rebalance + + + resize + + + + inflate Test case 1: inflate a node which has a leaf child node. =========================================================== step 1. prepare a fib trie ------------------------------------------ ip r a 192.168.0.0/24 via 192.168.11.1 ip r a 192.168.1.0/24 via 192.168.11.1 we get a fib trie. root@baker:~# cat /proc/net/fib_trie Main: +-- 192.168.0.0/23 1 0 0 |-- 192.168.0.0 /24 universe UNICAST |-- 192.168.1.0 /24 universe UNICAST Local: ..... step 2. Add the third route ------------------------------------------ root@baker:~# ip r a 192.168.2.0/24 via 192.168.11.1 A fib_trie leaf will be inserted in fib_insert_node before trie_rebalance. For function 'inflate': 'inflate' is called with following trie. +-- 192.168.0.0/22 1 1 0 <=== tn node +-- 192.168.0.0/23 1 0 0 <== node a |-- 192.168.0.0 /24 universe UNICAST |-- 192.168.1.0 /24 universe UNICAST |-- 192.168.2.0 <== leaf(node b) When process node b, which is a leaf. here: i is 1, node key "192.168.2.0" oldnode is (pos:22, bits:1) unpatch source: tkey_extract_bits(node->key, oldtnode->pos + oldtnode->bits, 1) it equals: tkey_extract_bits("192.168,2,0", 22 + 1, 1) thus got 0, and call put_child(tn, 2*i, node); <== 2*i=2. patched source: tkey_extract_bits(node->key, oldtnode->pos, oldtnode->bits + 1), tkey_extract_bits("192.168,2,0", 22, 1 + 1) <== get 2. Test case 2: inflate a node which has a an child node with skipped bits ========================================================================== step 1. prepare a fib trie. ip link set eth0 up ip a add dev eth0 192.168.11.1/32 ip r a 192.168.128.0/24 via 192.168.11.1 ip r a 192.168.0.0/24 via 192.168.11.1 ip r a 192.168.16.0/24 via 192.168.11.1 ip r a 192.168.32.0/24 via 192.168.11.1 ip r a 192.168.48.0/24 via 192.168.11.1 ip r a 192.168.144.0/24 via 192.168.11.1 ip r a 192.168.160.0/24 via 192.168.11.1 ip r a 192.168.176.0/24 via 192.168.11.1 check: root@baker:~# cat /proc/net/fib_trie Main: +-- 192.168.0.0/16 1 0 0 +-- 192.168.0.0/18 2 0 0 |-- 192.168.0.0 /24 universe UNICAST |-- 192.168.16.0 /24 universe UNICAST |-- 192.168.32.0 /24 universe UNICAST |-- 192.168.48.0 /24 universe UNICAST +-- 192.168.128.0/18 2 0 0 |-- 192.168.128.0 /24 universe UNICAST |-- 192.168.144.0 /24 universe UNICAST |-- 192.168.160.0 /24 universe UNICAST |-- 192.168.176.0 /24 universe UNICAST Local: ... step 2. add a route to trigger inflate. ip r a 192.168.96.0/24 via 192.168.11.1 This command will call serveral times inflate. In the first time, the fib_trie is: ________________________ +-- 192.168.128.0/(16, 1) <== tn node +-- 192.168.0.0/(17, 1) <== node a +-- 192.168.0.0/(18, 2) |-- 192.168.0.0 |-- 192.168.16.0 |-- 192.168.32.0 |-- 192.168.48.0 |-- 192.168.96.0 +-- 192.168.128.0/(18, 2) <== node b. |-- 192.168.128.0 |-- 192.168.144.0 |-- 192.168.160.0 |-- 192.168.176.0 NOTE: node b is a interal node with skipped bits. here, i:1, node->key "192.168.128.0", oldnode:(pos:16, bits:1) so tkey_extract_bits(node->key, oldtnode->pos + oldtnode->bits, 1) it equals: tkey_extract_bits("192.168,128,0", 16 + 1, 1) <=== 0 tkey_extract_bits(node->key, oldtnode->pos, oldtnode->bits, 1) it equals: tkey_extract_bits("192.168,128,0", 16, 1+1) <=== 2 2*i + 0 == 2, so the result is same. Signed-off-by: baker.zhang Signed-off-by: David S. Miller --- net/ipv4/fib_trie.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-) diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c index 3df6d3edb2a1..45c74ba03970 100644 --- a/net/ipv4/fib_trie.c +++ b/net/ipv4/fib_trie.c @@ -762,12 +762,9 @@ static struct tnode *inflate(struct trie *t, struct tnode *tn) if (IS_LEAF(node) || ((struct tnode *) node)->pos > tn->pos + tn->bits - 1) { - if (tkey_extract_bits(node->key, - oldtnode->pos + oldtnode->bits, - 1) == 0) - put_child(tn, 2*i, node); - else - put_child(tn, 2*i+1, node); + put_child(tn, + tkey_extract_bits(node->key, oldtnode->pos, oldtnode->bits + 1), + node); continue; }