On Tue, Sep 24, 2013 at 10:32:38AM +0100, Alexander Frolkin wrote:
> 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@xxxxxxxxxxxxxx>
Hi Alexander,
could you add some comments to the code or at least a description of the
algorithm to the above the function. The intent of original code may not
have been obvious to the eye but this version certainly isn't obvious to
mine.
> --
> diff --git a/net/netfilter/ipvs/ip_vs_sh.c b/net/netfilter/ipvs/ip_vs_sh.c
> index 3588fae..0db7d01 100644
> --- a/net/netfilter/ipvs/ip_vs_sh.c
> +++ b/net/netfilter/ipvs/ip_vs_sh.c
> @@ -120,22 +120,33 @@ 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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