From 567e4b79731c352a17d73c483959f795d3593e03 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Fri, 6 Feb 2015 12:59:01 -0800 Subject: 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 Acked-by: Tom Herbert Signed-off-by: David S. Miller --- net/core/dev.c | 48 +++++++++++++++++++++++++++--------------------- 1 file changed, 27 insertions(+), 21 deletions(-) (limited to 'net/core/dev.c') diff --git a/net/core/dev.c b/net/core/dev.c index a3a96ffc67f4..8be38675e1a8 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -3030,6 +3030,8 @@ static inline void ____napi_schedule(struct softnet_data *sd, /* One global table that all flow-based protocols share. */ struct rps_sock_flow_table __rcu *rps_sock_flow_table __read_mostly; EXPORT_SYMBOL(rps_sock_flow_table); +u32 rps_cpu_mask __read_mostly; +EXPORT_SYMBOL(rps_cpu_mask); struct static_key rps_needed __read_mostly; @@ -3086,16 +3088,17 @@ set_rps_cpu(struct net_device *dev, struct sk_buff *skb, static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb, struct rps_dev_flow **rflowp) { - struct netdev_rx_queue *rxqueue; - struct rps_map *map; + const struct rps_sock_flow_table *sock_flow_table; + struct netdev_rx_queue *rxqueue = dev->_rx; struct rps_dev_flow_table *flow_table; - struct rps_sock_flow_table *sock_flow_table; + struct rps_map *map; int cpu = -1; - u16 tcpu; + u32 tcpu; u32 hash; if (skb_rx_queue_recorded(skb)) { u16 index = skb_get_rx_queue(skb); + if (unlikely(index >= dev->real_num_rx_queues)) { WARN_ONCE(dev->real_num_rx_queues > 1, "%s received packet on queue %u, but number " @@ -3103,39 +3106,40 @@ static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb, dev->name, index, dev->real_num_rx_queues); goto done; } - rxqueue = dev->_rx + index; - } else - rxqueue = dev->_rx; + rxqueue += index; + } + /* Avoid computing hash if RFS/RPS is not active for this rxqueue */ + + flow_table = rcu_dereference(rxqueue->rps_flow_table); map = rcu_dereference(rxqueue->rps_map); - if (map) { - if (map->len == 1 && - !rcu_access_pointer(rxqueue->rps_flow_table)) { - tcpu = map->cpus[0]; - if (cpu_online(tcpu)) - cpu = tcpu; - goto done; - } - } else if (!rcu_access_pointer(rxqueue->rps_flow_table)) { + if (!flow_table && !map) goto done; - } skb_reset_network_header(skb); hash = skb_get_hash(skb); if (!hash) goto done; - flow_table = rcu_dereference(rxqueue->rps_flow_table); sock_flow_table = rcu_dereference(rps_sock_flow_table); if (flow_table && sock_flow_table) { - u16 next_cpu; struct rps_dev_flow *rflow; + u32 next_cpu; + u32 ident; + + /* First check into global flow table if there is a match */ + ident = sock_flow_table->ents[hash & sock_flow_table->mask]; + if ((ident ^ hash) & ~rps_cpu_mask) + goto try_rps; + next_cpu = ident & rps_cpu_mask; + + /* OK, now we know there is a match, + * we can look at the local (per receive queue) flow table + */ rflow = &flow_table->flows[hash & flow_table->mask]; tcpu = rflow->cpu; - next_cpu = sock_flow_table->ents[hash & sock_flow_table->mask]; - /* * If the desired CPU (where last recvmsg was done) is * different from current CPU (one in the rx-queue flow @@ -3162,6 +3166,8 @@ static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb, } } +try_rps: + if (map) { tcpu = map->cpus[reciprocal_scale(hash, map->len)]; if (cpu_online(tcpu)) { -- cgit v1.2.3