From: Eric Dumazet Date: Mon, 7 Apr 2025 16:35:59 +0000 (+0000) Subject: net: rps: change skb_flow_limit() hash function X-Git-Tag: v6.16-rc1~132^2~358^2~3 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=c3025e94daa9ce84ef0e53df983b5bf2fbd76ea6;p=thirdparty%2Fkernel%2Flinux.git net: rps: change skb_flow_limit() hash function As explained in commit f3483c8e1da6 ("net: rfs: hash function change"), masking low order bits of skb_get_hash(skb) has low entropy. A NIC with 32 RX queues uses the 5 low order bits of rss key to select a queue. This means all packets landing to a given queue share the same 5 low order bits. Switch to hash_32() to reduce hash collisions. Signed-off-by: Eric Dumazet Reviewed-by: Willem de Bruijn Link: https://patch.msgid.link/20250407163602.170356-2-edumazet@google.com Signed-off-by: Jakub Kicinski --- diff --git a/net/core/dev.c b/net/core/dev.c index 0608605cfc242..f674236f34beb 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -5038,7 +5038,7 @@ static bool skb_flow_limit(struct sk_buff *skb, unsigned int qlen) rcu_read_lock(); fl = rcu_dereference(sd->flow_limit); if (fl) { - new_flow = skb_get_hash(skb) & (fl->num_buckets - 1); + new_flow = hash_32(skb_get_hash(skb), fl->log_buckets); old_flow = fl->history[fl->history_head]; fl->history[fl->history_head] = new_flow; diff --git a/net/core/dev.h b/net/core/dev.h index 7ee203395d8e2..b1cd44b5f009b 100644 --- a/net/core/dev.h +++ b/net/core/dev.h @@ -16,7 +16,7 @@ struct cpumask; #define FLOW_LIMIT_HISTORY (1 << 7) /* must be ^2 and !overflow buckets */ struct sd_flow_limit { u64 count; - unsigned int num_buckets; + u8 log_buckets; unsigned int history_head; u16 history[FLOW_LIMIT_HISTORY]; u8 buckets[]; diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c index c7769ee0d9c55..5cfe76ede5237 100644 --- a/net/core/sysctl_net_core.c +++ b/net/core/sysctl_net_core.c @@ -248,7 +248,7 @@ static int flow_limit_cpu_sysctl(const struct ctl_table *table, int write, ret = -ENOMEM; goto write_unlock; } - cur->num_buckets = netdev_flow_limit_table_len; + cur->log_buckets = ilog2(netdev_flow_limit_table_len); rcu_assign_pointer(sd->flow_limit, cur); } }