Re: [PATCHv2] ipvs: improved SH fallback strategy
From: Alexander Frolkin <hidden>
Date: 2013-09-27 10:06:45
Also in:
lkml, lvs-devel
Subsystem:
ipvs, netfilter, networking [general], the rest · Maintainers:
Simon Horman, Julian Anastasov, Pablo Neira Ayuso, Florian Westphal, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
Improve the SH fallback realserver selection strategy. With sh and sh-fallback, if a realserver is down, this attempts to distribute the traffic that would have gone to that server evenly among the remaining servers. Signed-off-by: Alexander Frolkin <redacted> --
diff --git a/net/netfilter/ipvs/ip_vs_sh.c b/net/netfilter/ipvs/ip_vs_sh.c
index 3588fae..cc65b2f 100644
--- a/net/netfilter/ipvs/ip_vs_sh.c
+++ b/net/netfilter/ipvs/ip_vs_sh.c@@ -115,27 +115,46 @@ ip_vs_sh_get(struct ip_vs_service *svc, struct ip_vs_sh_state *s, } -/* As ip_vs_sh_get, but with fallback if selected server is unavailable */ +/* As ip_vs_sh_get, but with fallback if selected server is unavailable + * + * The fallback strategy loops around the table starting from a "random" + * point (in fact, it is chosen to be the original hash value to make the + * algorithm deterministic) to find a new server. + */ static inline struct ip_vs_dest * ip_vs_sh_get_fallback(struct ip_vs_service *svc, struct ip_vs_sh_state *s, const union nf_inet_addr *addr, __be16 port) { - unsigned int offset; - unsigned int hash; + unsigned int offset, roffset; + unsigned int hash, ihash; struct ip_vs_dest *dest; + /* first try the dest it's supposed to go to */ + ihash = ip_vs_sh_hashkey(svc->af, addr, port, 0); + dest = rcu_dereference(s->buckets[ihash].dest); + if (!dest) + return NULL; + if (!is_unavailable(dest)) + return dest; + + IP_VS_DBG_BUF(6, "SH: selected unavailable server %s:%d, reselecting", + IP_VS_DBG_ADDR(svc->af, &dest->addr), ntohs(dest->port)); + + /* if the original dest is unavailable, loop around the table + * starting from ihash to find a new dest + */ for (offset = 0; offset < IP_VS_SH_TAB_SIZE; offset++) { - hash = ip_vs_sh_hashkey(svc->af, addr, port, offset); + roffset = (offset + ihash) % IP_VS_SH_TAB_SIZE; + hash = ip_vs_sh_hashkey(svc->af, addr, port, roffset); dest = rcu_dereference(s->buckets[hash].dest); if (!dest) break; - if (is_unavailable(dest)) - IP_VS_DBG_BUF(6, "SH: selected unavailable server " - "%s:%d (offset %d)", - IP_VS_DBG_ADDR(svc->af, &dest->addr), - ntohs(dest->port), offset); - else + if (!is_unavailable(dest)) return dest; + IP_VS_DBG_BUF(6, "SH: selected unavailable " + "server %s:%d (offset %d), reselecting", + IP_VS_DBG_ADDR(svc->af, &dest->addr), + ntohs(dest->port), roffset); } return NULL;