[PATCH net-next v2] net/smc: Reduce overflow of smc clcsock listen queue

D. Wythe
2022-01-04T13:12:47Z

From: "D. Wythe" <alibuda@linux.alibaba.com>

In nginx/wrk multithread and 10K connections benchmark, the
backend TCP connection established very slowly, and lots of TCP
connections stay in SYN_SENT state.

Server: smc_run nginx

Client: smc_run wrk -c 10000 -t 4 http://server

Socket state in client host (wrk) shows like:

ss -t | wc -l
10000

ss -t | grep "SYN-SENT" | wc -l
6248

While the socket state in server host (nginx) shows like:

ss -t | wc -l
3752

Furthermore, the netstate of server host shows like:
145042 times the listen queue of a socket overflowed
145042 SYNs to LISTEN sockets dropped

This issue caused by smc_listen_work(), since the smc_tcp_listen_work()
shared the same workqueue (smc_hs_wq) with smc_listen_work(), while
smc_listen_work() do blocking wait for smc connection established, which
meanwhile block the accept() from TCP listen queue.

This patch creates a independent workqueue(smc_tcp_ls_wq) for
smc_tcp_listen_work(), separate it from smc_listen_work(), which is
quite acceptable considering that smc_tcp_listen_work() runs very fast.

After this patch, the smc 10K connections benchmark in my case is 5
times faster than before.

Before patch :

smc_run ./wrk -c 10000 -t 3 -d 20 http://server
3 threads and 10000 connections
143300 requests in 20.04s, 94.29MB read
Requests/sec: 7150.33
Transfer/sec: 4.70MB

After patch:

smc_run ./wrk -c 10000 -t 3 -d 20 http://server
3 threads and 10000 connections
902091 requests in 21.99s, 593.56MB read
Requests/sec: 41017.52
Transfer/sec: 26.99MB

Signed-off-by: D. Wythe <alibuda@linux.alibaba.com>
Reviewed-by: Tony Lu <tonylu@linux.alibaba.com>
---
changelog:
v2: code format
---
net/smc/af_smc.c | 13 +++++++++++--
net/smc/smc.h | 1 +
2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index 0bb614e..08722c0 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c
@@ -62,6 +62,7 @@
* creation on client
*/

+struct workqueue_struct *smc_tcp_ls_wq; /* wq for tcp listen work */
struct workqueue_struct *smc_hs_wq; /* wq for handshake work */
struct workqueue_struct *smc_close_wq; /* wq for close work */

@@ -1872,7 +1873,7 @@ static void smc_clcsock_data_ready(struct sock *listen_clcsock)
lsmc->clcsk_data_ready(listen_clcsock);
if (lsmc->sk.sk_state == SMC_LISTEN) {
sock_hold(&lsmc->sk); /* sock_put in smc_tcp_listen_work() */
- if (!queue_work(smc_hs_wq, &lsmc->tcp_listen_work))
+ if (!queue_work(smc_tcp_ls_wq, &lsmc->tcp_listen_work))
sock_put(&lsmc->sk);
}
}
@@ -2610,9 +2611,14 @@ static int __init smc_init(void)
goto out_nl;

rc = -ENOMEM;
+
+ smc_tcp_ls_wq = alloc_workqueue("smc_tcp_ls_wq", 0, 0);
+ if (!smc_tcp_ls_wq)
+ goto out_pnet;
+
smc_hs_wq = alloc_workqueue("smc_hs_wq", 0, 0);
if (!smc_hs_wq)
- goto out_pnet;
+ goto out_alloc_tcp_ls_wq;

smc_close_wq = alloc_workqueue("smc_close_wq", 0, 0);
if (!smc_close_wq)
@@ -2709,6 +2715,8 @@ static int __init smc_init(void)
destroy_workqueue(smc_close_wq);
out_alloc_hs_wq:
destroy_workqueue(smc_hs_wq);
+out_alloc_tcp_ls_wq:
+ destroy_workqueue(smc_tcp_ls_wq);
out_pnet:
smc_pnet_exit();
out_nl:
@@ -2728,6 +2736,7 @@ static void __exit smc_exit(void)
smc_core_exit();
smc_ib_unregister_client();
destroy_workqueue(smc_close_wq);
+ destroy_workqueue(smc_tcp_ls_wq);
destroy_workqueue(smc_hs_wq);
proto_unregister(&smc_proto6);
proto_unregister(&smc_proto);
diff --git a/net/smc/smc.h b/net/smc/smc.h
index b1d6625..18fa803 100644
--- a/net/smc/smc.h
+++ b/net/smc/smc.h
@@ -256,6 +256,7 @@ static inline struct smc_sock *smc_sk(const struct sock *sk)
return (struct smc_sock *)sk;
}

+extern struct workqueue_struct *smc_tcp_ls_wq; /* wq for tcp listen work */
extern struct workqueue_struct *smc_hs_wq; /* wq for handshake work */
extern struct workqueue_struct *smc_close_wq; /* wq for close work */

--
1.8.3.1