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Date: Sun, 3 Apr 2022 14:06:15 +0100 From: Pavel Begunkov <asml.silence@...il.com> To: netdev@...r.kernel.org, "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org> Cc: Eric Dumazet <edumazet@...gle.com>, Wei Liu <wei.liu@...nel.org>, Paul Durrant <paul@....org>, Pavel Begunkov <asml.silence@...il.com> Subject: [PATCH net-next 03/27] sock: optimise sock_def_write_space barriers Now we have a separate path for sock_def_write_space() and can go one step further. When it's called from sock_wfree() we know that there is a preceding atomic for putting down ->sk_wmem_alloc. We can use it to replace to replace smb_mb() with a less expensive smp_mb__after_atomic(). It also removes an extra RCU read lock/unlock as a small bonus. Signed-off-by: Pavel Begunkov <asml.silence@...il.com> --- net/core/sock.c | 26 +++++++++++++++++++++++++- 1 file changed, 25 insertions(+), 1 deletion(-) diff --git a/net/core/sock.c b/net/core/sock.c index 9389bb602c64..b1a8f47fda55 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -144,6 +144,7 @@ static DEFINE_MUTEX(proto_list_mutex); static LIST_HEAD(proto_list); +static void sock_def_write_space_wfree(struct sock *sk); static void sock_def_write_space(struct sock *sk); /** @@ -2309,7 +2310,7 @@ void sock_wfree(struct sk_buff *skb) sk->sk_write_space == sock_def_write_space) { rcu_read_lock(); free = refcount_sub_and_test(len, &sk->sk_wmem_alloc); - sock_def_write_space(sk); + sock_def_write_space_wfree(sk); rcu_read_unlock(); if (unlikely(free)) __sk_free(sk); @@ -3201,6 +3202,29 @@ static void sock_def_write_space(struct sock *sk) rcu_read_unlock(); } +/* An optimised version of sock_def_write_space(), should only be called + * for SOCK_RCU_FREE sockets under RCU read section and after putting + * ->sk_wmem_alloc. + */ +static void sock_def_write_space_wfree(struct sock *sk) +{ + /* Do not wake up a writer until he can make "significant" + * progress. --DaveM + */ + if (sock_writeable(sk)) { + struct socket_wq *wq = rcu_dereference(sk->sk_wq); + + /* rely on refcount_sub from sock_wfree() */ + smp_mb__after_atomic(); + if (wq && waitqueue_active(&wq->wait)) + wake_up_interruptible_sync_poll(&wq->wait, EPOLLOUT | + EPOLLWRNORM | EPOLLWRBAND); + + /* Should agree with poll, otherwise some programs break */ + sk_wake_async(sk, SOCK_WAKE_SPACE, POLL_OUT); + } +} + static void sock_def_destruct(struct sock *sk) { } -- 2.35.1
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