Re: [PATCH mptcp-next] mptcp: use fast lock for subflows when possible.

[Mat Martineau <mathew.j.martineau@linux.intel.com>]

On Wed, 26 May 2021, Paolo Abeni wrote:

> There are a bunch of callsite where the ssk socket
> lock is acquired using the full-blown version eligible for
> the fast variant. Let's move to the latter.
>
> Signed-off-by: Paolo Abeni <pabeni@redhat.com>
> ---
> The previous patch demonstrated that using lock_sock()
> were the fast version is available can have worse side-effect
> than slower performances.
>
> This tries to address the topic.
> ---
> net/mptcp/pm_netlink.c | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)

Looks good to me, thanks Paolo.

Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>

-Mat


>
> diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
> index 09722598994d..d4732a4f223e 100644
> --- a/net/mptcp/pm_netlink.c
> +++ b/net/mptcp/pm_netlink.c
> @@ -540,6 +540,7 @@ void mptcp_pm_nl_addr_send_ack(struct mptcp_sock *msk)
> 	subflow = list_first_entry_or_null(&msk->conn_list, typeof(*subflow), node);
> 	if (subflow) {
> 		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
> +		bool slow;
>
> 		spin_unlock_bh(&msk->pm.lock);
> 		pr_debug("send ack for %s%s%s",
> @@ -547,9 +548,9 @@ void mptcp_pm_nl_addr_send_ack(struct mptcp_sock *msk)
> 			 mptcp_pm_should_add_signal_ipv6(msk) ? " [ipv6]" : "",
> 			 mptcp_pm_should_add_signal_port(msk) ? " [port]" : "");
>
> -		lock_sock(ssk);
> +		slow = lock_sock_fast(ssk);
> 		tcp_send_ack(ssk);
> -		release_sock(ssk);
> +		unlock_sock_fast(ssk, slow);
> 		spin_lock_bh(&msk->pm.lock);
> 	}
> }
> @@ -566,6 +567,7 @@ int mptcp_pm_nl_mp_prio_send_ack(struct mptcp_sock *msk,
> 		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
> 		struct sock *sk = (struct sock *)msk;
> 		struct mptcp_addr_info local;
> +		bool slow;
>
> 		local_address((struct sock_common *)ssk, &local);
> 		if (!addresses_equal(&local, addr, addr->port))
> @@ -578,9 +580,9 @@ int mptcp_pm_nl_mp_prio_send_ack(struct mptcp_sock *msk,
>
> 		spin_unlock_bh(&msk->pm.lock);
> 		pr_debug("send ack for mp_prio");
> -		lock_sock(ssk);
> +		slow = lock_sock_fast(ssk);
> 		tcp_send_ack(ssk);
> -		release_sock(ssk);
> +		unlock_sock_fast(ssk, slow);
> 		spin_lock_bh(&msk->pm.lock);
>
> 		return 0;
> -- 
> 2.26.3
>
>
>

--
Mat Martineau
Intel