diff mbox

[10/16] ipv4: Cache output routes in fib_info nexthops.

Message ID 20120719.143540.747492487297004222.davem@davemloft.net
State Changes Requested, archived
Delegated to: David Miller
Headers show

Commit Message

David Miller July 19, 2012, 9:35 p.m. UTC 
If we have an output route that lacks nexthop exceptions, we can cache
it in the FIB info nexthop.

Such routes will have DST_HOST cleared because such routes refer to a
family of destinations, rather than just one.

The sequence of the handling of exceptions during route lookup is
adjusted to make the logic work properly.

Before we allocate the route, we lookup the exception.

Then we know if we will cache this route or not, and therefore whether
DST_HOST should be set on the allocated route.

Then we use DST_HOST to key off whether we should store the resulting
route, during rt_set_nexthop(), in the FIB nexthop cache.

Signed-off-by: David S. Miller <davem@davemloft.net>
---
 include/net/ip_fib.h     |    2 +
 net/ipv4/fib_semantics.c |    2 +
 net/ipv4/route.c         |  134 +++++++++++++++++++++++++++++++---------------
 3 files changed, 95 insertions(+), 43 deletions(-)

Comments

Eric Dumazet July 19, 2012, 10:09 p.m. UTC | #1 
On Thu, 2012-07-19 at 14:35 -0700, David Miller wrote:
> If we have an output route that lacks nexthop exceptions, we can cache
> it in the FIB info nexthop.
> 
> Such routes will have DST_HOST cleared because such routes refer to a
> family of destinations, rather than just one.
> 
> The sequence of the handling of exceptions during route lookup is
> adjusted to make the logic work properly.
> 
> Before we allocate the route, we lookup the exception.
> 
> Then we know if we will cache this route or not, and therefore whether
> DST_HOST should be set on the allocated route.
> 
> Then we use DST_HOST to key off whether we should store the resulting
> route, during rt_set_nexthop(), in the FIB nexthop cache.
> 
> Signed-off-by: David S. Miller <davem@davemloft.net>


> +static void rt_cache_route(struct fib_nh *nh, struct rtable *rt)
> +{
> +	struct rtable *orig, *prev, **p = &nh->nh_rth_output;
> +
> +	orig = *p;
> +
> +	prev = cmpxchg(p, orig, rt);
> +	if (prev == orig) {
> +		dst_clone(&rt->dst);
> +		if (orig)
> +			dst_release(&orig->dst);
>  	}
>  }
>  

Hmm...

If we find orig not null, what can protect another cpu from reading
nh->nh_rth_output, then we dst_release(orig), and other cpu  does the
dst_use() too late ?



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David Miller July 19, 2012, 10:13 p.m. UTC | #2 
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Fri, 20 Jul 2012 00:09:03 +0200

> If we find orig not null, what can protect another cpu from reading
> nh->nh_rth_output, then we dst_release(orig), and other cpu  does the
> dst_use() too late ?

Indeed, we'd have to defer it somehow.

Actually, we might be able to fake this by using __dst_free() on it
or something similar.

But safest would be RCU, whose protection we are still using on the
read side.

Any better ideas?


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Eric Dumazet July 19, 2012, 10:19 p.m. UTC | #3 
On Thu, 2012-07-19 at 15:13 -0700, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@gmail.com>
> Date: Fri, 20 Jul 2012 00:09:03 +0200
> 
> > If we find orig not null, what can protect another cpu from reading
> > nh->nh_rth_output, then we dst_release(orig), and other cpu  does the
> > dst_use() too late ?
> 
> Indeed, we'd have to defer it somehow.
> 
> Actually, we might be able to fake this by using __dst_free() on it
> or something similar.
> 
> But safest would be RCU, whose protection we are still using on the
> read side.
> 
> Any better ideas?

Well, its very late for me in France and I really need to sleep.

I hope I really can, now that you gave me the silly idea to work on a
linux patch ;)

RCU seems a good idea at first glance.



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diff mbox

Patch

diff --git a/include/net/ip_fib.h b/include/net/ip_fib.h
index 2daf096..fb62c59 100644
--- a/include/net/ip_fib.h
+++ b/include/net/ip_fib.h
@@ -46,6 +46,7 @@  struct fib_config {
  };
 
 struct fib_info;
+struct rtable;
 
 struct fib_nh_exception {
 	struct fib_nh_exception __rcu	*fnhe_next;
@@ -80,6 +81,7 @@  struct fib_nh {
 	__be32			nh_gw;
 	__be32			nh_saddr;
 	int			nh_saddr_genid;
+	struct rtable		*nh_rth_output;
 	struct fnhe_hash_bucket	*nh_exceptions;
 };
 
diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index 2b57d76..83d0f42 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -171,6 +171,8 @@  static void free_fib_info_rcu(struct rcu_head *head)
 			dev_put(nexthop_nh->nh_dev);
 		if (nexthop_nh->nh_exceptions)
 			free_nh_exceptions(nexthop_nh);
+		if (nexthop_nh->nh_rth_output)
+			dst_release(&nexthop_nh->nh_rth_output->dst);
 	} endfor_nexthops(fi);
 
 	release_net(fi->fib_net);
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index f902d08..8d8b3b2 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1158,8 +1158,7 @@  static unsigned int ipv4_mtu(const struct dst_entry *dst)
 	return mtu;
 }
 
-static void rt_init_metrics(struct rtable *rt, const struct flowi4 *fl4,
-			    struct fib_info *fi)
+static void rt_init_metrics(struct rtable *rt, struct fib_info *fi)
 {
 	if (fi->fib_metrics != (u32 *) dst_default_metrics) {
 		rt->fi = fi;
@@ -1168,50 +1167,77 @@  static void rt_init_metrics(struct rtable *rt, const struct flowi4 *fl4,
 	dst_init_metrics(&rt->dst, fi->fib_metrics, true);
 }
 
-static void rt_bind_exception(struct rtable *rt, struct fib_nh *nh, __be32 daddr)
+static struct fib_nh_exception *find_exception(struct fib_nh *nh, __be32 daddr)
 {
 	struct fnhe_hash_bucket *hash = nh->nh_exceptions;
 	struct fib_nh_exception *fnhe;
 	u32 hval;
 
+	if (!hash)
+		return NULL;
+
 	hval = fnhe_hashfun(daddr);
 
-restart:
 	for (fnhe = rcu_dereference(hash[hval].chain); fnhe;
 	     fnhe = rcu_dereference(fnhe->fnhe_next)) {
-		__be32 fnhe_daddr, gw;
-		unsigned long expires;
-		unsigned int seq;
-		u32 pmtu;
-
-		seq = read_seqbegin(&fnhe_seqlock);
-		fnhe_daddr = fnhe->fnhe_daddr;
-		gw = fnhe->fnhe_gw;
-		pmtu = fnhe->fnhe_pmtu;
-		expires = fnhe->fnhe_expires;
-		if (read_seqretry(&fnhe_seqlock, seq))
-			goto restart;
-		if (daddr != fnhe_daddr)
-			continue;
-		if (pmtu) {
-			unsigned long diff = expires - jiffies;
+		if (fnhe->fnhe_daddr == daddr)
+			return fnhe;
+	}
+	return NULL;
+}
 
-			if (time_before(jiffies, expires)) {
-				rt->rt_pmtu = pmtu;
-				dst_set_expires(&rt->dst, diff);
-			}
-		}
-		if (gw) {
-			rt->rt_flags |= RTCF_REDIRECTED;
-			rt->rt_gateway = gw;
+static void rt_bind_exception(struct rtable *rt, struct fib_nh_exception *fnhe,
+			      __be32 daddr)
+{
+	__be32 fnhe_daddr, gw;
+	unsigned long expires;
+	unsigned int seq;
+	u32 pmtu;
+
+restart:
+	seq = read_seqbegin(&fnhe_seqlock);
+	fnhe_daddr = fnhe->fnhe_daddr;
+	gw = fnhe->fnhe_gw;
+	pmtu = fnhe->fnhe_pmtu;
+	expires = fnhe->fnhe_expires;
+	if (read_seqretry(&fnhe_seqlock, seq))
+		goto restart;
+
+	if (daddr != fnhe_daddr)
+		return;
+
+	if (pmtu) {
+		unsigned long diff = expires - jiffies;
+
+		if (time_before(jiffies, expires)) {
+			rt->rt_pmtu = pmtu;
+			dst_set_expires(&rt->dst, diff);
 		}
-		fnhe->fnhe_stamp = jiffies;
-		break;
+	}
+	if (gw) {
+		rt->rt_flags |= RTCF_REDIRECTED;
+		rt->rt_gateway = gw;
+	}
+	fnhe->fnhe_stamp = jiffies;
+}
+
+static void rt_cache_route(struct fib_nh *nh, struct rtable *rt)
+{
+	struct rtable *orig, *prev, **p = &nh->nh_rth_output;
+
+	orig = *p;
+
+	prev = cmpxchg(p, orig, rt);
+	if (prev == orig) {
+		dst_clone(&rt->dst);
+		if (orig)
+			dst_release(&orig->dst);
 	}
 }
 
-static void rt_set_nexthop(struct rtable *rt, const struct flowi4 *fl4,
+static void rt_set_nexthop(struct rtable *rt, __be32 daddr,
 			   const struct fib_result *res,
+			   struct fib_nh_exception *fnhe,
 			   struct fib_info *fi, u16 type, u32 itag)
 {
 	if (fi) {
@@ -1219,12 +1245,15 @@  static void rt_set_nexthop(struct rtable *rt, const struct flowi4 *fl4,
 
 		if (nh->nh_gw && nh->nh_scope == RT_SCOPE_LINK)
 			rt->rt_gateway = nh->nh_gw;
-		if (unlikely(nh->nh_exceptions))
-			rt_bind_exception(rt, nh, fl4->daddr);
-		rt_init_metrics(rt, fl4, fi);
+		if (unlikely(fnhe))
+			rt_bind_exception(rt, fnhe, daddr);
+		rt_init_metrics(rt, fi);
 #ifdef CONFIG_IP_ROUTE_CLASSID
-		rt->dst.tclassid = FIB_RES_NH(*res).nh_tclassid;
+		rt->dst.tclassid = nh->nh_tclassid;
 #endif
+		if (!(rt->dst.flags & DST_HOST) &&
+		    rt_is_output_route(rt))
+			rt_cache_route(nh, rt);
 	}
 
 #ifdef CONFIG_IP_ROUTE_CLASSID
@@ -1236,10 +1265,10 @@  static void rt_set_nexthop(struct rtable *rt, const struct flowi4 *fl4,
 }
 
 static struct rtable *rt_dst_alloc(struct net_device *dev,
-				   bool nopolicy, bool noxfrm)
+				   bool nopolicy, bool noxfrm, bool will_cache)
 {
 	return dst_alloc(&ipv4_dst_ops, dev, 1, DST_OBSOLETE_FORCE_CHK,
-			 DST_HOST | DST_NOCACHE |
+			 (will_cache ? 0 : DST_HOST) | DST_NOCACHE |
 			 (nopolicy ? DST_NOPOLICY : 0) |
 			 (noxfrm ? DST_NOXFRM : 0));
 }
@@ -1276,7 +1305,7 @@  static int ip_route_input_mc(struct sk_buff *skb, __be32 daddr, __be32 saddr,
 			goto e_err;
 	}
 	rth = rt_dst_alloc(dev_net(dev)->loopback_dev,
-			   IN_DEV_CONF_GET(in_dev, NOPOLICY), false);
+			   IN_DEV_CONF_GET(in_dev, NOPOLICY), false, false);
 	if (!rth)
 		goto e_nobufs;
 
@@ -1349,6 +1378,7 @@  static int __mkroute_input(struct sk_buff *skb,
 			   __be32 daddr, __be32 saddr, u32 tos,
 			   struct rtable **result)
 {
+	struct fib_nh_exception *fnhe;
 	struct rtable *rth;
 	int err;
 	struct in_device *out_dev;
@@ -1395,9 +1425,13 @@  static int __mkroute_input(struct sk_buff *skb,
 		}
 	}
 
+	fnhe = NULL;
+	if (res->fi)
+		fnhe = find_exception(&FIB_RES_NH(*res), daddr);
+
 	rth = rt_dst_alloc(out_dev->dev,
 			   IN_DEV_CONF_GET(in_dev, NOPOLICY),
-			   IN_DEV_CONF_GET(out_dev, NOXFRM));
+			   IN_DEV_CONF_GET(out_dev, NOXFRM), false);
 	if (!rth) {
 		err = -ENOBUFS;
 		goto cleanup;
@@ -1416,7 +1450,7 @@  static int __mkroute_input(struct sk_buff *skb,
 	rth->dst.input = ip_forward;
 	rth->dst.output = ip_output;
 
-	rt_set_nexthop(rth, NULL, res, res->fi, res->type, itag);
+	rt_set_nexthop(rth, daddr, res, fnhe, res->fi, res->type, itag);
 
 	*result = rth;
 	err = 0;
@@ -1558,7 +1592,7 @@  brd_input:
 
 local_input:
 	rth = rt_dst_alloc(net->loopback_dev,
-			   IN_DEV_CONF_GET(in_dev, NOPOLICY), false);
+			   IN_DEV_CONF_GET(in_dev, NOPOLICY), false, false);
 	if (!rth)
 		goto e_nobufs;
 
@@ -1672,6 +1706,7 @@  static struct rtable *__mkroute_output(const struct fib_result *res,
 				       unsigned int flags)
 {
 	struct fib_info *fi = res->fi;
+	struct fib_nh_exception *fnhe;
 	struct in_device *in_dev;
 	u16 type = res->type;
 	struct rtable *rth;
@@ -1710,9 +1745,22 @@  static struct rtable *__mkroute_output(const struct fib_result *res,
 			fi = NULL;
 	}
 
+	fnhe = NULL;
+	if (fi) {
+		fnhe = find_exception(&FIB_RES_NH(*res), fl4->daddr);
+		if (!fnhe) {
+			rth = FIB_RES_NH(*res).nh_rth_output;
+			if (rth &&
+			    rth->dst.obsolete == DST_OBSOLETE_FORCE_CHK) {
+				dst_use(&rth->dst, jiffies);
+				return rth;
+			}
+		}
+	}
 	rth = rt_dst_alloc(dev_out,
 			   IN_DEV_CONF_GET(in_dev, NOPOLICY),
-			   IN_DEV_CONF_GET(in_dev, NOXFRM));
+			   IN_DEV_CONF_GET(in_dev, NOXFRM),
+			   fi && !fnhe);
 	if (!rth)
 		return ERR_PTR(-ENOBUFS);
 
@@ -1749,7 +1797,7 @@  static struct rtable *__mkroute_output(const struct fib_result *res,
 #endif
 	}
 
-	rt_set_nexthop(rth, fl4, res, fi, type, 0);
+	rt_set_nexthop(rth, fl4->daddr, res, fnhe, fi, type, 0);
 
 	if (fl4->flowi4_flags & FLOWI_FLAG_RT_NOCACHE)
 		rth->dst.flags |= DST_NOCACHE;