Commit 6b229cf7 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

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: default avatarEric Dumazet <>
Signed-off-by: default avatarDavid S. Miller <>
parent c84d9490
......@@ -79,6 +79,9 @@ struct udp_sock {
int (*gro_complete)(struct sock *sk,
struct sk_buff *skb,
int nhoff);
/* This field is dirtied by udp_recvmsg() */
int forward_deficit;
static inline struct udp_sock *udp_sk(const struct sock *sk)
......@@ -1177,8 +1177,20 @@ out:
/* fully reclaim rmem/fwd memory allocated for skb */
static void udp_rmem_release(struct sock *sk, int size, int partial)
struct udp_sock *up = udp_sk(sk);
int amt;
if (likely(partial)) {
up->forward_deficit += size;
size = up->forward_deficit;
if (size < (sk->sk_rcvbuf >> 2) &&
} else {
size += up->forward_deficit;
up->forward_deficit = 0;
atomic_sub(size, &sk->sk_rmem_alloc);
sk->sk_forward_alloc += size;
amt = (sk->sk_forward_alloc - partial) & ~(SK_MEM_QUANTUM - 1);
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