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Subject[PATCH] ipvs: improved SH fallback strategy
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 <avf@eldamar.org.uk>
---
diff --git a/net/netfilter/ipvs/ip_vs_sh.c b/net/netfilter/ipvs/ip_vs_sh.c
index f16c027..1676354 100644
--- a/net/netfilter/ipvs/ip_vs_sh.c
+++ b/net/netfilter/ipvs/ip_vs_sh.c
@@ -120,22 +120,35 @@ 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;

- for (offset = 0; offset < IP_VS_SH_TAB_SIZE; offset++) {
- hash = ip_vs_sh_hashkey(svc->af, addr, port, offset);
- 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)",
+ 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)) {
+ IP_VS_DBG_BUF(6, "SH: selected unavailable server "
+ "%s:%d, reselecting",
+ IP_VS_DBG_ADDR(svc->af, &dest->addr),
+ ntohs(dest->port));
+ for (offset = 0; offset < IP_VS_SH_TAB_SIZE; 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 (is_unavailable(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), offset);
- else
- return dest;
+ ntohs(dest->port), roffset);
+ else
+ return dest;
+ }
+ } else {
+ return dest;
}

return NULL;


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