From 345aa031207d02d7438c1aa96ed9315911ecd745 Mon Sep 17 00:00:00 2001 From: Jarek Poplawski Date: Tue, 7 Jul 2009 19:39:16 -0700 Subject: [PATCH] ipv4: Fix fib_trie rebalancing, part 4 (root thresholds) Pawel Staszewski wrote:
Some time ago i report this: http://bugzilla.kernel.org/show_bug.cgi?id=6648 and now with 2.6.29 / 2.6.29.1 / 2.6.29.3 and 2.6.30 it back dmesg output: oprofile: using NMI interrupt. Fix inflate_threshold_root. Now=15 size=11 bits ... Fix inflate_threshold_root. Now=15 size=11 bits cat /proc/net/fib_triestat Basic info: size of leaf: 40 bytes, size of tnode: 56 bytes. Main: Aver depth: 2.28 Max depth: 6 Leaves: 276539 Prefixes: 289922 Internal nodes: 66762 1: 35046 2: 13824 3: 9508 4: 4897 5: 2331 6: 1149 7: 5 9: 1 18: 1 Pointers: 691228 Null ptrs: 347928 Total size: 35709 kB
It seems, the current threshold for root resizing is too aggressive, and it causes misleading warnings during big updates, but it might be also responsible for memory problems, especially with non-preempt configs, when RCU freeing is delayed long after call_rcu. It should be also mentioned that because of non-atomic changes during resizing/rebalancing the current lookup algorithm can miss valid leaves so it's additional argument to shorten these activities even at a cost of a minimally longer searching. This patch restores values before the patch "[IPV4]: fib_trie root node settings", commit: 965ffea43d4ebe8cd7b9fee78d651268dd7d23c5 from v2.6.22. Pawel's report:
I dont see any big change of (cpu load or faster/slower routing/propagating routes from bgpd or something else) - in avg there is from 2% to 3% more of CPU load i dont know why but it is - i change from "preempt" to "no preempt" 3 times and check this my "mpstat -P ALL 1 30" always avg cpu load was from 2 to 3% more compared to "no preempt" [...] cat /proc/net/fib_triestat Basic info: size of leaf: 20 bytes, size of tnode: 36 bytes. Main: Aver depth: 2.44 Max depth: 6 Leaves: 277814 Prefixes: 291306 Internal nodes: 66420 1: 32737 2: 14850 3: 10332 4: 4871 5: 2313 6: 942 7: 371 8: 3 17: 1 Pointers: 599098 Null ptrs: 254865 Total size: 18067 kB
According to this and other similar reports average depth is slightly increased (~0.2), and root nodes are shorter (log 17 vs. 18), but there is no visible performance decrease. So, until memory handling is improved or added parameters for changing this individually, this patch resets to safer defaults. Reported-by: Pawel Staszewski Reported-by: Jorge Boncompte [DTI2] Signed-off-by: Jarek Poplawski Tested-by: Pawel Staszewski Signed-off-by: David S. Miller --- net/ipv4/fib_trie.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c index 00a54b246dfe..63c2fa7b68c4 100644 --- a/net/ipv4/fib_trie.c +++ b/net/ipv4/fib_trie.c @@ -316,8 +316,8 @@ static inline void check_tnode(const struct tnode *tn) static const int halve_threshold = 25; static const int inflate_threshold = 50; -static const int halve_threshold_root = 8; -static const int inflate_threshold_root = 15; +static const int halve_threshold_root = 15; +static const int inflate_threshold_root = 25; static void __alias_free_mem(struct rcu_head *head) -- 2.20.1