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Re: [PATCH] Sloppy TCP, SH rebalancing, SHP scheduling

To: Julian Anastasov <ja@xxxxxx>
Subject: Re: [PATCH] Sloppy TCP, SH rebalancing, SHP scheduling
Cc: lvs-devel@xxxxxxxxxxxxxxx
From: Alexander Frolkin <avf@xxxxxxxxxxxxxx>
Date: Wed, 12 Jun 2013 15:10:18 +0100
Hi,

> > I just don't understand why rejecting a client connection when there are
> > servers available is desirable behaviour.
>       The problem is that every move leads to problems:
> - add/remove destination => mapping is changed for all dests
> - set weight to 0 and allow fallback => mapping is changed for
>       two connections from same IP

Fair enough, although I would guess two connections from the same IP
going to different servers wouldn't be an issue in many cases.

> - persistence implemented with SH => fallback is risky. Usually,
> we use expire_quiescent_template for such cases when persistence
> is used.

Can you elaborate on what you mean by "risky" here?

> - same mapping for many directors => fallback is desired when
> config is same on all directors and persistence behaviour is
> not desired.

Indeed.

> Not sure if we can apply the expire_quiescent_template flag to
> the SH scheduler to control fallback.

But then it's controlled by a sysctl, not per virtual server, which is
something we didn't want, I believe.

Are you happy for me to go ahead and add the per-service scheduler
flags (IP_VS_SVC_F_SCHED1, etc.), like you suggested previously?

At the moment, the patch looks like this (pending a decision on how to
enable the features):

diff --git a/net/netfilter/ipvs/ip_vs_sh.c b/net/netfilter/ipvs/ip_vs_sh.c
index 0df269d..abd8ed6 100644
--- a/net/netfilter/ipvs/ip_vs_sh.c
+++ b/net/netfilter/ipvs/ip_vs_sh.c
@@ -48,6 +48,10 @@
 
 #include <net/ip_vs.h>
 
+#include <net/tcp.h>
+#include <linux/udp.h>
+#include <linux/sctp.h>
+
 
 /*
  *      IPVS SH bucket
@@ -74,7 +78,9 @@ struct ip_vs_sh_state {
 /*
  *     Returns hash value for IPVS SH entry
  */
-static inline unsigned int ip_vs_sh_hashkey(int af, const union nf_inet_addr 
*addr)
+static inline unsigned int ip_vs_sh_hashkey(int af,
+       const union nf_inet_addr *addr, __be16 port,
+       unsigned int offset)
 {
        __be32 addr_fold = addr->ip;
 
@@ -83,7 +89,8 @@ static inline unsigned int ip_vs_sh_hashkey(int af, const 
union nf_inet_addr *ad
                addr_fold = addr->ip6[0]^addr->ip6[1]^
                            addr->ip6[2]^addr->ip6[3];
 #endif
-       return (ntohl(addr_fold)*2654435761UL) & IP_VS_SH_TAB_MASK;
+       return (offset + (ntohs(port) + ntohl(addr_fold))*2654435761UL) &
+               IP_VS_SH_TAB_MASK;
 }
 
 
@@ -91,9 +98,11 @@ static inline unsigned int ip_vs_sh_hashkey(int af, const 
union nf_inet_addr *ad
  *      Get ip_vs_dest associated with supplied parameters.
  */
 static inline struct ip_vs_dest *
-ip_vs_sh_get(int af, struct ip_vs_sh_state *s, const union nf_inet_addr *addr)
+ip_vs_sh_get(int af, struct ip_vs_sh_state *s, const union nf_inet_addr *addr,
+       __be16 port, unsigned int offset)
 {
-       return rcu_dereference(s->buckets[ip_vs_sh_hashkey(af, addr)].dest);
+       return rcu_dereference(
+               s->buckets[ip_vs_sh_hashkey(af, addr, port, offset)].dest);
 }
 
 
@@ -232,17 +241,43 @@ ip_vs_sh_schedule(struct ip_vs_service *svc, const struct 
sk_buff *skb)
        struct ip_vs_dest *dest;
        struct ip_vs_sh_state *s;
        struct ip_vs_iphdr iph;
+       unsigned int offset;
+       unsigned int found;
 
        ip_vs_fill_iph_addr_only(svc->af, skb, &iph);
 
        IP_VS_DBG(6, "ip_vs_sh_schedule(): Scheduling...\n");
 
+       /* XXX if L4 hash */
+       if (0)
+               port = ip_vs_sh_get_port(svc, skb, iph);
+       else
+               port = 0;
+
        s = (struct ip_vs_sh_state *) svc->sched_data;
-       dest = ip_vs_sh_get(svc->af, s, &iph.saddr);
-       if (!dest
-           || !(dest->flags & IP_VS_DEST_F_AVAILABLE)
-           || atomic_read(&dest->weight) <= 0
-           || is_overloaded(dest)) {
+       /* XXX if fallback */
+       if (0) {
+               found = 0;
+               for (offset = 0; offset < IP_VS_SH_TAB_SIZE; offset++) {
+                       dest = ip_vs_sh_get(svc->af, s, &iph.saddr,
+                               port, offset);
+                       if (!is_available(dest)) {
+                               IP_VS_DBG_BUF(6, "SH: selected unavailable"
+                                       "server %s:%d, retrying with offset"
+                                       "%d\n",
+                                       IP_VS_DBG_ADDR(svc->af, &dest->addr),
+                                       ntohs(dest->port),
+                                       offset);
+                       } else {
+                               found = 1;
+                               break;
+                       }
+               }
+       } else {
+               dest = ip_vs_sh_get(svc->af, s, &iph.saddr, port, 0);
+               found = 1;
+       }
+       if (!found || !is_available(dest)) {
                ip_vs_scheduler_err(svc, "no destination available");
                return NULL;
        }
@@ -255,6 +290,50 @@ ip_vs_sh_schedule(struct ip_vs_service *svc, const struct 
sk_buff *skb)
        return dest;
 }
 
+/*
+ *     Helper function to determine if server is available
+ */
+static inline int
+is_available(struct ip_vs_dest *dest)
+{
+       return (!dest ||
+               !(dest->flags & IP_VS_DEST_F_AVAILABLE) ||
+               atomic_read(&dest->weight) <= 0 ||
+               is_overloaded(dest))
+}
+
+/*
+ *     Helper function to get port number
+ */
+static inline __be16
+ip_vs_sh_get_port(struct ip_vs_service *svc, const struct sk_buff *skb,
+       struct ip_vs_iphdr iph)
+{
+       __be16 port;
+       struct tcphdr _tcph, *th;
+       struct udphdr _udph, *uh;
+       sctp_sctphdr_t _sctph, *sh;
+
+       switch (svc->protocol) {
+       case IPPROTO_TCP:
+               th = skb_header_pointer(skb, iph.len, sizeof(_tcph), &_tcph);
+               port = th->source;
+               break;
+       case IPPROTO_UDP:
+               uh = skb_header_pointer(skb, iph.len, sizeof(_udph), &_udph);
+               port = uh->source;
+               break;
+       case IPPROTO_SCTP:
+               sh = skb_header_pointer(skb, iph.len, sizeof(_sctph), &_sctph);
+               port = sh->source;
+               break;
+       default:
+               port = 0;
+       }
+
+       return port;
+}
+
 
 /*
  *      IPVS SH Scheduler structure


Alex

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