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Message-ID: <20250324223243.76632-1-kuniyu@amazon.com>
Date: Mon, 24 Mar 2025 15:32:15 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <edumazet@...gle.com>
CC: <davem@...emloft.net>, <eric.dumazet@...il.com>, <horms@...nel.org>,
<kuba@...nel.org>, <kuniyu@...zon.com>, <ncardwell@...gle.com>,
<netdev@...r.kernel.org>, <pabeni@...hat.com>
Subject: Re: [PATCH net-next] tcp: avoid atomic operations on sk->sk_rmem_alloc
From: Eric Dumazet <edumazet@...gle.com>
Date: Thu, 20 Mar 2025 12:16:04 +0000
> TCP uses generic skb_set_owner_r() and sock_rfree()
> for received packets, with socket lock being owned.
>
> Switch to private versions, avoiding two atomic operations
> per packet.
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> ---
> include/net/tcp.h | 15 +++++++++++++++
> net/ipv4/tcp.c | 18 ++++++++++++++++--
> net/ipv4/tcp_fastopen.c | 2 +-
> net/ipv4/tcp_input.c | 6 +++---
> 4 files changed, 35 insertions(+), 6 deletions(-)
>
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index d08fbf90495de69b157d3c87c50e82d781a365df..dd6d63a6f42b99774e9461b69d3e7932cf629082 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -779,6 +779,7 @@ static inline int tcp_bound_to_half_wnd(struct tcp_sock *tp, int pktsize)
>
> /* tcp.c */
> void tcp_get_info(struct sock *, struct tcp_info *);
> +void tcp_sock_rfree(struct sk_buff *skb);
>
> /* Read 'sendfile()'-style from a TCP socket */
> int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
> @@ -2898,4 +2899,18 @@ enum skb_drop_reason tcp_inbound_hash(struct sock *sk,
> const void *saddr, const void *daddr,
> int family, int dif, int sdif);
>
> +/* version of skb_set_owner_r() avoiding one atomic_add() */
> +static inline void tcp_skb_set_owner_r(struct sk_buff *skb, struct sock *sk)
> +{
> + skb_orphan(skb);
> + skb->sk = sk;
> + skb->destructor = tcp_sock_rfree;
> +
> + sock_owned_by_me(sk);
> + atomic_set(&sk->sk_rmem_alloc,
> + atomic_read(&sk->sk_rmem_alloc) + skb->truesize);
It's nice to learn that atomic_set() and _read() are just __WRITE_ONCE()
and __READ_ONCE() and have no LOCK_PREFIX :)
Reviewed-by: Kuniyuki Iwashima <kuniyu@...zon.com>
Thanks!
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