From 9e8445a56c253f01f6716ac14526a7dae6bc0d46 Mon Sep 17 00:00:00 2001 From: Paolo Abeni Date: Wed, 4 Apr 2018 14:30:01 +0200 Subject: [PATCH] net: avoid unneeded atomic operation in ip*_append_data() After commit 694aba690de0 ("ipv4: factorize sk_wmem_alloc updates done by __ip_append_data()") and commit 1f4c6eb24029 ("ipv6: factorize sk_wmem_alloc updates done by __ip6_append_data()"), when transmitting sub MTU datagram, an addtional, unneeded atomic operation is performed in ip*_append_data() to update wmem_alloc: in the above condition the delta is 0. The above cause small but measurable performance regression in UDP xmit tput test with packet size below MTU. This change avoids such overhead updating wmem_alloc only if wmem_alloc_delta is non zero. The error path is left intentionally unmodified: it's a slow path and simplicity is preferred to performances. Fixes: 694aba690de0 ("ipv4: factorize sk_wmem_alloc updates done by __ip_append_data()") Fixes: 1f4c6eb24029 ("ipv6: factorize sk_wmem_alloc updates done by __ip6_append_data()") Signed-off-by: Paolo Abeni Reviewed-by: Eric Dumazet Signed-off-by: David S. Miller --- net/ipv4/ip_output.c | 3 ++- net/ipv6/ip6_output.c | 3 ++- 2 files changed, 4 insertions(+), 2 deletions(-) diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c index 94cacae76aca..4c11b810a447 100644 --- a/net/ipv4/ip_output.c +++ b/net/ipv4/ip_output.c @@ -1090,7 +1090,8 @@ alloc_new_skb: length -= copy; } - refcount_add(wmem_alloc_delta, &sk->sk_wmem_alloc); + if (wmem_alloc_delta) + refcount_add(wmem_alloc_delta, &sk->sk_wmem_alloc); return 0; error_efault: diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c index 66a768b7b8fb..b8ee50e94af3 100644 --- a/net/ipv6/ip6_output.c +++ b/net/ipv6/ip6_output.c @@ -1545,7 +1545,8 @@ alloc_new_skb: length -= copy; } - refcount_add(wmem_alloc_delta, &sk->sk_wmem_alloc); + if (wmem_alloc_delta) + refcount_add(wmem_alloc_delta, &sk->sk_wmem_alloc); return 0; error_efault: -- 2.30.2