net/smc: Make smc_tcp_listen_work() independent

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

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

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

One reason of this issue is that, since the smc_tcp_listen_work() shared
the same workqueue (smc_hs_wq) with smc_listen_work(), while the
smc_listen_work() do blocking wait for smc connection established. Once
the workqueue became congested, it's will block the accept() from TCP
listen.

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.

Signed-off-by: D. Wythe <alibuda@linux.alibaba.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index 00b2e9d..4969ac8 100644 (file)
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c
@@ -59,6 +59,7 @@ static DEFINE_MUTEX(smc_client_lgr_pending);  /* serialize link group
                                                 * creation on client
                                                 */
 
+static 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 */
 
@@ -2227,7 +2228,7 @@ 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);
        }
 }
@@ -3024,9 +3025,14 @@ 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)
@@ -3097,6 +3103,8 @@ out_alloc_wqs:
        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:
@@ -3115,6 +3123,7 @@ 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);