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SubjectRe: [PATCHv2] ipvs: improved SH fallback strategy

Hello,

On Fri, 27 Sep 2013, 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@eldamar.org.uk>

Thanks! Looks good to me.

Acked-by: Julian Anastasov <ja@ssi.bg>

> --
> 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;

Regards

--
Julian Anastasov <ja@ssi.bg>


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