net: rfs: add hash collision detection
Receive Flow Steering is a nice solution but suffers from
hash collisions when a mix of connected and unconnected traffic
is received on the host, when flow hash table is populated.
Also, clearing flow in inet_release() makes RFS not very good
for short lived flows, as many packets can follow close().
(FIN , ACK packets, ...)
This patch extends the information stored into global hash table
to not only include cpu number, but upper part of the hash value.
I use a 32bit value, and dynamically split it in two parts.
For host with less than 64 possible cpus, this gives 6 bits for the
cpu number, and 26 (32-6) bits for the upper part of the hash.
Since hash bucket selection use low order bits of the hash, we have
a full hash match, if /proc/sys/net/core/rps_sock_flow_entries is big
enough.
If the hash found in flow table does not match, we fallback to RPS (if
it is enabled for the rxqueue).
This means that a packet for an non connected flow can avoid the
IPI through a unrelated/victim CPU.
This also means we no longer have to clear the table at socket
close time, and this helps short lived flows performance.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/sock.h b/include/net/sock.h
index d28b8fe..e138245 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -857,18 +857,6 @@
#endif
}
-static inline void sock_rps_reset_flow_hash(__u32 hash)
-{
-#ifdef CONFIG_RPS
- struct rps_sock_flow_table *sock_flow_table;
-
- rcu_read_lock();
- sock_flow_table = rcu_dereference(rps_sock_flow_table);
- rps_reset_sock_flow(sock_flow_table, hash);
- rcu_read_unlock();
-#endif
-}
-
static inline void sock_rps_record_flow(const struct sock *sk)
{
#ifdef CONFIG_RPS
@@ -876,28 +864,18 @@
#endif
}
-static inline void sock_rps_reset_flow(const struct sock *sk)
-{
-#ifdef CONFIG_RPS
- sock_rps_reset_flow_hash(sk->sk_rxhash);
-#endif
-}
-
static inline void sock_rps_save_rxhash(struct sock *sk,
const struct sk_buff *skb)
{
#ifdef CONFIG_RPS
- if (unlikely(sk->sk_rxhash != skb->hash)) {
- sock_rps_reset_flow(sk);
+ if (unlikely(sk->sk_rxhash != skb->hash))
sk->sk_rxhash = skb->hash;
- }
#endif
}
static inline void sock_rps_reset_rxhash(struct sock *sk)
{
#ifdef CONFIG_RPS
- sock_rps_reset_flow(sk);
sk->sk_rxhash = 0;
#endif
}