udp: add batching to udp_rmem_release()
If udp_recvmsg() constantly releases sk_rmem_alloc for every read packet, it gives opportunity for producers to immediately grab spinlocks and desperatly try adding another packet, causing false sharing. We can add a simple heuristic to give the signal by batches of ~25 % of the queue capacity. This patch considerably increases performance under flood by about 50 %, since the thread draining the queue is no longer slowed by false sharing. Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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@ -79,6 +79,9 @@ struct udp_sock {
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int (*gro_complete)(struct sock *sk,
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struct sk_buff *skb,
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int nhoff);
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/* This field is dirtied by udp_recvmsg() */
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int forward_deficit;
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};
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static inline struct udp_sock *udp_sk(const struct sock *sk)
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@ -1177,8 +1177,20 @@ out:
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/* fully reclaim rmem/fwd memory allocated for skb */
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static void udp_rmem_release(struct sock *sk, int size, int partial)
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{
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struct udp_sock *up = udp_sk(sk);
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int amt;
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if (likely(partial)) {
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up->forward_deficit += size;
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size = up->forward_deficit;
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if (size < (sk->sk_rcvbuf >> 2) &&
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!skb_queue_empty(&sk->sk_receive_queue))
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return;
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} else {
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size += up->forward_deficit;
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}
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up->forward_deficit = 0;
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atomic_sub(size, &sk->sk_rmem_alloc);
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sk->sk_forward_alloc += size;
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amt = (sk->sk_forward_alloc - partial) & ~(SK_MEM_QUANTUM - 1);
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