Subject: Re: [PATCH net-next 2/3] RDS-TCP: Do not bloat sndbuf/rcvbuf in rds_tcp_tune

From: santosh shilimkar <[email-masked]>
Date: Wed, 30 Sep 2015 08:54:23 -0700

On 9/30/2015 6:45 AM, Sowmini Varadhan wrote:
> Using the value of RDS_TCP_DEFAULT_BUFSIZE (128K)
> clobbers efficient use of TSO because it inflates the size_goal
> that is computed in tcp_sendmsg/tcp_sendpage and skews packet
> latency, and the default values for these parameters actually
> results in significantly better performance.
>
> In request-response tests using rds-stress with a packet size of
> 100K with 16 threads (test parameters -q 100000 -a 256 -t16 -d16)
> between a single pair of IP addresses achieves a throughput of
> 6-8 Gbps. Without this patch, throughput maxes at 2-3 Gbps under
> equivalent conditions on these platforms.
>
> Signed-off-by: Sowmini Varadhan <[email-masked]>
> ---
>   net/rds/tcp.c |   16 ++++------------
>   1 files changed, 4 insertions(+), 12 deletions(-)
>
> diff --git a/net/rds/tcp.c b/net/rds/tcp.c
> index c42b60b..9d6ddba 100644
> --- a/net/rds/tcp.c
> +++ b/net/rds/tcp.c
> @@ -67,21 +67,13 @@ void rds_tcp_nonagle(struct socket *sock)
>   	set_fs(oldfs);
>   }
>
> +/* All module specific customizations to the RDS-TCP socket should be done in
> + * rds_tcp_tune() and applied after socket creation. In general these
> + * customizations should be tunable via module_param()
> + */
>   void rds_tcp_tune(struct socket *sock)
>   {
> -	struct sock *sk = sock->sk;
> -
>   	rds_tcp_nonagle(sock);
> -
> -	/*
> -	 * We're trying to saturate gigabit with the default,
> -	 * see svc_sock_setbufsize().
> -	 */
> -	lock_sock(sk);
> -	sk->sk_sndbuf = RDS_TCP_DEFAULT_BUFSIZE;
> -	sk->sk_rcvbuf = RDS_TCP_DEFAULT_BUFSIZE;
> -	sk->sk_userlocks |= SOCK_SNDBUF_LOCK|SOCK_RCVBUF_LOCK;
> -	release_sock(sk);
>   }
>
>   u32 rds_tcp_snd_nxt(struct rds_tcp_connection *tc)
>
We should at least start with sndbuf/rcvbuf parameters.
Nice work. Almost ~3X lift in RDS TCP performance.

Acked-by: Santosh Shilimkar <[email-masked]>