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

From: santosh shilimkar
Date: Wed Sep 30 2015 - 11:54:59 EST

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 <sowmini.varadhan@xxxxxxxxxx>
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)

+/* 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;
- /*
- * 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 <santosh.shilimkar@xxxxxxxxxx>
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