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Date: Wed, 25 Jul 2012 17:54:06 -0700 (PDT)
From: David Miller <davem@...emloft.net>
To: alexander.duyck@...il.com
Cc: eric.dumazet@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH 00/16] Remove the ipv4 routing cache
From: David Miller <davem@...emloft.net>
Date: Wed, 25 Jul 2012 16:39:39 -0700 (PDT)
> From: David Miller <davem@...emloft.net>
> Date: Wed, 25 Jul 2012 16:17:32 -0700 (PDT)
>
>> From: Alexander Duyck <alexander.duyck@...il.com>
>> Date: Wed, 25 Jul 2012 16:02:45 -0700
>>
>>> Since your patches are in I have started to re-run my tests. I am
>>> seeing a significant drop in throughput with 8 flows which I expected,
>>> however it looks like one of the biggest issues I am seeing is that
>>> the dst_hold and dst_release calls seem to be causing some serious
>>> cache thrash. I was at 12.5Mpps w/ 8 flows before the patches, after
>>> your patches it drops to 8.3Mpps.
>>
>> Yes, this is something we knew would start happening.
>>
>> One idea is to make cached dsts be per-cpu in the nexthops.
>
> Actually I think what really kills your case is the removal of the
> noref path for route lookups. I'll work on a patch to restore that
> in the case where we use cached routes from the FIB nexthops.
Alex, here is something I tossed together, does it help with the
dst_hold()/dst_release() overhead at all?
diff --git a/include/net/route.h b/include/net/route.h
index c29ef27..8c52bc6 100644
--- a/include/net/route.h
+++ b/include/net/route.h
@@ -30,6 +30,7 @@
#include <net/inet_sock.h>
#include <linux/in_route.h>
#include <linux/rtnetlink.h>
+#include <linux/rcupdate.h>
#include <linux/route.h>
#include <linux/ip.h>
#include <linux/cache.h>
@@ -157,8 +158,22 @@ static inline struct rtable *ip_route_output_gre(struct net *net, struct flowi4
return ip_route_output_key(net, fl4);
}
-extern int ip_route_input(struct sk_buff *skb, __be32 dst, __be32 src,
- u8 tos, struct net_device *devin);
+extern int ip_route_input_noref(struct sk_buff *skb, __be32 dst, __be32 src,
+ u8 tos, struct net_device *devin);
+
+static inline int ip_route_input(struct sk_buff *skb, __be32 dst, __be32 src,
+ u8 tos, struct net_device *devin)
+{
+ int err;
+
+ rcu_read_lock();
+ err = ip_route_input_noref(skb, dst, src, tos, devin);
+ if (!err)
+ skb_dst_force(skb);
+ rcu_read_unlock();
+
+ return err;
+}
extern void ipv4_update_pmtu(struct sk_buff *skb, struct net *net, u32 mtu,
int oif, u32 mark, u8 protocol, int flow_flags);
diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
index a0124eb..77e87af 100644
--- a/net/ipv4/arp.c
+++ b/net/ipv4/arp.c
@@ -827,7 +827,7 @@ static int arp_process(struct sk_buff *skb)
}
if (arp->ar_op == htons(ARPOP_REQUEST) &&
- ip_route_input(skb, tip, sip, 0, dev) == 0) {
+ ip_route_input_noref(skb, tip, sip, 0, dev) == 0) {
rt = skb_rtable(skb);
addr_type = rt->rt_type;
diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c
index 7ad88e5..8d07c97 100644
--- a/net/ipv4/ip_fragment.c
+++ b/net/ipv4/ip_fragment.c
@@ -258,8 +258,8 @@ static void ip_expire(unsigned long arg)
/* skb dst is stale, drop it, and perform route lookup again */
skb_dst_drop(head);
iph = ip_hdr(head);
- err = ip_route_input(head, iph->daddr, iph->saddr,
- iph->tos, head->dev);
+ err = ip_route_input_noref(head, iph->daddr, iph->saddr,
+ iph->tos, head->dev);
if (err)
goto out_rcu_unlock;
diff --git a/net/ipv4/ip_input.c b/net/ipv4/ip_input.c
index 93134b0..bda8cac 100644
--- a/net/ipv4/ip_input.c
+++ b/net/ipv4/ip_input.c
@@ -339,8 +339,8 @@ static int ip_rcv_finish(struct sk_buff *skb)
* how the packet travels inside Linux networking.
*/
if (!skb_dst(skb)) {
- int err = ip_route_input(skb, iph->daddr, iph->saddr,
- iph->tos, skb->dev);
+ int err = ip_route_input_noref(skb, iph->daddr, iph->saddr,
+ iph->tos, skb->dev);
if (unlikely(err)) {
if (err == -EXDEV)
NET_INC_STATS_BH(dev_net(skb->dev),
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 3f7bb71..68887e3 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1199,10 +1199,9 @@ restart:
fnhe->fnhe_stamp = jiffies;
}
-static inline void rt_release_rcu(struct rcu_head *head)
+static inline void rt_free(struct rtable *rt)
{
- struct dst_entry *dst = container_of(head, struct dst_entry, rcu_head);
- dst_release(dst);
+ call_rcu_bh(&rt->dst.rcu_head, dst_rcu_free);
}
static void rt_cache_route(struct fib_nh *nh, struct rtable *rt)
@@ -1216,9 +1215,15 @@ static void rt_cache_route(struct fib_nh *nh, struct rtable *rt)
prev = cmpxchg(p, orig, rt);
if (prev == orig) {
- dst_clone(&rt->dst);
if (orig)
- call_rcu_bh(&orig->dst.rcu_head, rt_release_rcu);
+ rt_free(orig);
+ } else {
+ /* Routes we intend to cache in the FIB nexthop have
+ * the DST_NOCACHE bit set. However, if we are
+ * unsuccessful at storing this route into the cache
+ * we really need to clear that bit.
+ */
+ rt->dst.flags &= ~DST_NOCACHE;
}
}
@@ -1245,7 +1250,7 @@ static void rt_set_nexthop(struct rtable *rt, __be32 daddr,
#ifdef CONFIG_IP_ROUTE_CLASSID
rt->dst.tclassid = nh->nh_tclassid;
#endif
- if (!(rt->dst.flags & DST_HOST))
+ if (!(rt->dst.flags & DST_NOCACHE))
rt_cache_route(nh, rt);
}
@@ -1261,7 +1266,7 @@ static struct rtable *rt_dst_alloc(struct net_device *dev,
bool nopolicy, bool noxfrm, bool will_cache)
{
return dst_alloc(&ipv4_dst_ops, dev, 1, DST_OBSOLETE_FORCE_CHK,
- (will_cache ? 0 : DST_HOST) | DST_NOCACHE |
+ (will_cache ? 0 : (DST_HOST | DST_NOCACHE)) |
(nopolicy ? DST_NOPOLICY : 0) |
(noxfrm ? DST_NOXFRM : 0));
}
@@ -1588,8 +1593,9 @@ local_input:
if (!itag) {
rth = FIB_RES_NH(res).nh_rth_input;
if (rt_cache_valid(rth)) {
- dst_hold(&rth->dst);
- goto set_and_out;
+ skb_dst_set_noref(skb, &rth->dst);
+ err = 0;
+ goto out;
}
do_cache = true;
}
@@ -1620,7 +1626,6 @@ local_input:
}
if (do_cache)
rt_cache_route(&FIB_RES_NH(res), rth);
-set_and_out:
skb_dst_set(skb, &rth->dst);
err = 0;
goto out;
@@ -1658,8 +1663,8 @@ martian_source_keep_err:
goto out;
}
-int ip_route_input(struct sk_buff *skb, __be32 daddr, __be32 saddr,
- u8 tos, struct net_device *dev)
+int ip_route_input_noref(struct sk_buff *skb, __be32 daddr, __be32 saddr,
+ u8 tos, struct net_device *dev)
{
int res;
@@ -1702,7 +1707,7 @@ int ip_route_input(struct sk_buff *skb, __be32 daddr, __be32 saddr,
rcu_read_unlock();
return res;
}
-EXPORT_SYMBOL(ip_route_input);
+EXPORT_SYMBOL(ip_route_input_noref);
/* called with rcu_read_lock() */
static struct rtable *__mkroute_output(const struct fib_result *res,
diff --git a/net/ipv4/xfrm4_input.c b/net/ipv4/xfrm4_input.c
index 58d23a5..06814b6 100644
--- a/net/ipv4/xfrm4_input.c
+++ b/net/ipv4/xfrm4_input.c
@@ -27,8 +27,8 @@ static inline int xfrm4_rcv_encap_finish(struct sk_buff *skb)
if (skb_dst(skb) == NULL) {
const struct iphdr *iph = ip_hdr(skb);
- if (ip_route_input(skb, iph->daddr, iph->saddr,
- iph->tos, skb->dev))
+ if (ip_route_input_noref(skb, iph->daddr, iph->saddr,
+ iph->tos, skb->dev))
goto drop;
}
return dst_input(skb);
--
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