From 1080d709fb9d8cd4392f93476ee46a9d6ea05a5b Mon Sep 17 00:00:00 2001 From: Neil Horman Date: Mon, 27 Oct 2008 12:28:25 -0700 Subject: net: implement emergency route cache rebulds when gc_elasticity is exceeded This is a patch to provide on demand route cache rebuilding. Currently, our route cache is rebulid periodically regardless of need. This introduced unneeded periodic latency. This patch offers a better approach. Using code provided by Eric Dumazet, we compute the standard deviation of the average hash bucket chain length while running rt_check_expire. Should any given chain length grow to larger that average plus 4 standard deviations, we trigger an emergency hash table rebuild for that net namespace. This allows for the common case in which chains are well behaved and do not grow unevenly to not incur any latency at all, while those systems (which may be being maliciously attacked), only rebuild when the attack is detected. This patch take 2 other factors into account: 1) chains with multiple entries that differ by attributes that do not affect the hash value are only counted once, so as not to unduly bias system to rebuilding if features like QOS are heavily used 2) if rebuilding crosses a certain threshold (which is adjustable via the added sysctl in this patch), route caching is disabled entirely for that net namespace, since constant rebuilding is less efficient that no caching at all Tested successfully by me. Signed-off-by: Neil Horman Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- Documentation/networking/ip-sysctl.txt | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'Documentation') diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt index d84932650fd..c7712787933 100644 --- a/Documentation/networking/ip-sysctl.txt +++ b/Documentation/networking/ip-sysctl.txt @@ -27,6 +27,12 @@ min_adv_mss - INTEGER The advertised MSS depends on the first hop route MTU, but will never be lower than this setting. +rt_cache_rebuild_count - INTEGER + The per net-namespace route cache emergency rebuild threshold. + Any net-namespace having its route cache rebuilt due to + a hash bucket chain being too long more than this many times + will have its route caching disabled + IP Fragmentation: ipfrag_high_thresh - INTEGER -- cgit v1.2.3