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Date: Thu, 2 Jan 2014 12:00:23 -0800 (PST)
From: Tom Herbert <therbert@...gle.com>
To: davem@...emloft.net, netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: [PATCH] ipv4: move rt_genid to different cache line
Running a simple netperf TCP_RR test with 200 clients shows that
ipv4_dst_check is high on the list of functions in 'perf top'. The
pertinent action in this function is in the call to rt_is_expired
which checks the route genid (rt->rt_gentid) against the global value.
rt_genid is in the same cacheline as dst->__refcnt which is causing
false sharing.
This fix moves rt_genid into the first cacheline of the dst structure.
The dst structue is explicitly packed for cacheline optimization, so to
make room for the genid, I moved xfrm to cacheline with __refcnt (under
the assumption it is less likely to be in the critical path).
I don't believe there is an issue in ip6_dst_check since rt6i_genid
and the dst are in separate cachelines already (struct rt6_info).
Signed-off-by: Tom Herbert <therbert@...gle.com>
---
include/net/dst.h | 10 ++++++----
include/net/route.h | 1 -
net/ipv4/route.c | 13 +++++++------
3 files changed, 13 insertions(+), 11 deletions(-)
diff --git a/include/net/dst.h b/include/net/dst.h
index 77eb53f..91777b2 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -39,10 +39,9 @@ struct dst_entry {
unsigned long expires;
struct dst_entry *path;
struct dst_entry *from;
-#ifdef CONFIG_XFRM
- struct xfrm_state *xfrm;
-#else
- void *__pad1;
+ int genid;
+#ifdef CONFIG_64BIT
+ int __pad0;
#endif
int (*input)(struct sk_buff *);
int (*output)(struct sk_buff *);
@@ -104,6 +103,9 @@ struct dst_entry {
struct rt6_info *rt6_next;
struct dn_route __rcu *dn_next;
};
+#ifdef CONFIG_XFRM
+ struct xfrm_state *xfrm;
+#endif
};
u32 *dst_cow_metrics_generic(struct dst_entry *dst, unsigned long old);
diff --git a/include/net/route.h b/include/net/route.h
index 638e3eb..72b4446 100644
--- a/include/net/route.h
+++ b/include/net/route.h
@@ -46,7 +46,6 @@ struct fib_info;
struct rtable {
struct dst_entry dst;
- int rt_genid;
unsigned int rt_flags;
__u16 rt_type;
__u8 rt_is_input;
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index f8da282..8936da8 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -436,7 +436,7 @@ static inline int ip_rt_proc_init(void)
static inline bool rt_is_expired(const struct rtable *rth)
{
- return rth->rt_genid != rt_genid_ipv4(dev_net(rth->dst.dev));
+ return rth->dst.genid != rt_genid_ipv4(dev_net(rth->dst.dev));
}
void rt_cache_flush(struct net *net)
@@ -1459,8 +1459,8 @@ static int ip_route_input_mc(struct sk_buff *skb, __be32 daddr, __be32 saddr,
rth->dst.tclassid = itag;
#endif
rth->dst.output = ip_rt_bug;
+ rth->dst.genid = rt_genid_ipv4(dev_net(dev));
- rth->rt_genid = rt_genid_ipv4(dev_net(dev));
rth->rt_flags = RTCF_MULTICAST;
rth->rt_type = RTN_MULTICAST;
rth->rt_is_input= 1;
@@ -1591,7 +1591,7 @@ static int __mkroute_input(struct sk_buff *skb,
goto cleanup;
}
- rth->rt_genid = rt_genid_ipv4(dev_net(rth->dst.dev));
+
rth->rt_flags = flags;
rth->rt_type = res->type;
rth->rt_is_input = 1;
@@ -1603,6 +1603,7 @@ static int __mkroute_input(struct sk_buff *skb,
rth->dst.input = ip_forward;
rth->dst.output = ip_output;
+ rth->dst.genid = rt_genid_ipv4(dev_net(rth->dst.dev));
rt_set_nexthop(rth, daddr, res, fnhe, res->fi, res->type, itag);
skb_dst_set(skb, &rth->dst);
@@ -1761,8 +1762,8 @@ local_input:
#ifdef CONFIG_IP_ROUTE_CLASSID
rth->dst.tclassid = itag;
#endif
+ rth->dst.genid = rt_genid_ipv4(net);
- rth->rt_genid = rt_genid_ipv4(net);
rth->rt_flags = flags|RTCF_LOCAL;
rth->rt_type = res.type;
rth->rt_is_input = 1;
@@ -1950,8 +1951,8 @@ add:
return ERR_PTR(-ENOBUFS);
rth->dst.output = ip_output;
+ rth->dst.genid = rt_genid_ipv4(dev_net(dev_out));
- rth->rt_genid = rt_genid_ipv4(dev_net(dev_out));
rth->rt_flags = flags;
rth->rt_type = type;
rth->rt_is_input = 0;
@@ -2228,12 +2229,12 @@ struct dst_entry *ipv4_blackhole_route(struct net *net, struct dst_entry *dst_or
new->dev = ort->dst.dev;
if (new->dev)
dev_hold(new->dev);
+ new->genid = rt_genid_ipv4(net);
rt->rt_is_input = ort->rt_is_input;
rt->rt_iif = ort->rt_iif;
rt->rt_pmtu = ort->rt_pmtu;
- rt->rt_genid = rt_genid_ipv4(net);
rt->rt_flags = ort->rt_flags;
rt->rt_type = ort->rt_type;
rt->rt_gateway = ort->rt_gateway;
--
1.8.5.1
--
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