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Date: Wed, 16 Feb 2022 11:49:03 +0800
From: Dust Li <dust.li@...ux.alibaba.com>
To: Karsten Graul <kgraul@...ux.ibm.com>,
Tony Lu <tonylu@...ux.alibaba.com>
Cc: kuba@...nel.org, davem@...emloft.net, netdev@...r.kernel.org,
linux-s390@...r.kernel.org, linux-rdma@...r.kernel.org
Subject: [PATCH] net/smc: Add autocork support
This patch adds autocork support for SMC which could improve
throughput for small message by x2 ~ x4.
The main idea is borrowed from TCP autocork with some RDMA
specific modification:
1. The first message should never cork to make sure we won't
bring extra latency
2. If we have posted any Tx WRs to the NIC that have not
completed, cork the new messages until:
a) Receive CQE for the last Tx WR
b) We have corked enough message on the connection
3. Try to push the corked data out when we receive CQE of
the last Tx WR to prevent the corked messages hang in
the send queue.
Both SMC autocork and TCP autocork check the TX completion
to decide whether we should cork or not. The difference is
when we got a SMC Tx WR completion, the data have been confirmed
by the RNIC while TCP TX completion just tells us the data
have been sent out by the local NIC.
Add an atomic variable tx_pushing in smc_connection to make
sure only one can send to let it cork more and save CDC slot.
SMC autocork should not bring extra latency since the first
message will always been sent out immediately.
The qperf tcp_bw test shows more than x4 increase under small
message size with Mellanox connectX4-Lx, same result with other
throughput benchmarks like sockperf/netperf.
The qperf tcp_lat test shows SMC autocork has not increase any
ping-pong latency.
BW test:
client: smc_run taskset -c 1 qperf smc-server -oo msg_size:1:64K:*2 \
-t 30 -vu tcp_bw
server: smc_run taskset -c 1 qperf
MsgSize(Bytes) TCP SMC-NoCork SMC-AutoCork
1 2.57 MB/s 698 KB/s(-73.5%) 2.98 MB/s(16.0% )
2 5.1 MB/s 1.41 MB/s(-72.4%) 5.82 MB/s(14.1% )
4 10.2 MB/s 2.83 MB/s(-72.3%) 11.7 MB/s(14.7% )
8 20.8 MB/s 5.62 MB/s(-73.0%) 22.9 MB/s(10.1% )
16 42.5 MB/s 11.5 MB/s(-72.9%) 45.5 MB/s(7.1% )
32 80.7 MB/s 22.3 MB/s(-72.4%) 86.7 MB/s(7.4% )
64 155 MB/s 45.6 MB/s(-70.6%) 160 MB/s(3.2% )
128 295 MB/s 90.1 MB/s(-69.5%) 273 MB/s(-7.5% )
256 539 MB/s 179 MB/s(-66.8%) 610 MB/s(13.2% )
512 943 MB/s 360 MB/s(-61.8%) 1.02 GB/s(10.8% )
1024 1.58 GB/s 710 MB/s(-56.1%) 1.91 GB/s(20.9% )
2048 2.47 GB/s 1.34 GB/s(-45.7%) 2.92 GB/s(18.2% )
4096 2.86 GB/s 2.5 GB/s(-12.6%) 2.4 GB/s(-16.1%)
8192 3.89 GB/s 3.14 GB/s(-19.3%) 4.05 GB/s(4.1% )
16384 3.29 GB/s 4.67 GB/s(41.9% ) 5.09 GB/s(54.7% )
32768 2.73 GB/s 5.48 GB/s(100.7%) 5.49 GB/s(101.1%)
65536 3 GB/s 4.85 GB/s(61.7% ) 5.24 GB/s(74.7% )
Latency test:
client: smc_run taskset -c 1 qperf smc-server -oo msg_size:1:64K:*2 \
-t 30 -vu tcp_lat
server: smc_run taskset -c 1 qperf
MsgSize SMC-NoCork SMC-AutoCork
1 9.7 us 9.6 us( -1.03%)
2 9.43 us 9.39 us( -0.42%)
4 9.6 us 9.35 us( -2.60%)
8 9.42 us 9.2 us( -2.34%)
16 9.13 us 9.43 us( 3.29%)
32 9.19 us 9.5 us( 3.37%)
64 9.38 us 9.5 us( 1.28%)
128 9.9 us 9.29 us( -6.16%)
256 9.42 us 9.26 us( -1.70%)
512 10 us 9.45 us( -5.50%)
1024 10.4 us 9.6 us( -7.69%)
2048 10.4 us 10.2 us( -1.92%)
4096 11 us 10.5 us( -4.55%)
8192 11.7 us 11.8 us( 0.85%)
16384 14.5 us 14.2 us( -2.07%)
32768 19.4 us 19.3 us( -0.52%)
65536 28.1 us 28.8 us( 2.49%)
With SMC autocork support, we can archive better throughput than
TCP in most message sizes without any latency tradeoff.
Signed-off-by: Dust Li <dust.li@...ux.alibaba.com>
---
net/smc/smc.h | 2 +
net/smc/smc_cdc.c | 11 +++--
net/smc/smc_tx.c | 118 ++++++++++++++++++++++++++++++++++++++++------
3 files changed, 114 insertions(+), 17 deletions(-)
diff --git a/net/smc/smc.h b/net/smc/smc.h
index a096d8af21a0..bc7df235281c 100644
--- a/net/smc/smc.h
+++ b/net/smc/smc.h
@@ -192,6 +192,8 @@ struct smc_connection {
* - dec on polled tx cqe
*/
wait_queue_head_t cdc_pend_tx_wq; /* wakeup on no cdc_pend_tx_wr*/
+ atomic_t tx_pushing; /* nr_threads trying tx push */
+
struct delayed_work tx_work; /* retry of smc_cdc_msg_send */
u32 tx_off; /* base offset in peer rmb */
diff --git a/net/smc/smc_cdc.c b/net/smc/smc_cdc.c
index 9d5a97168969..2b37bec90824 100644
--- a/net/smc/smc_cdc.c
+++ b/net/smc/smc_cdc.c
@@ -48,9 +48,14 @@ static void smc_cdc_tx_handler(struct smc_wr_tx_pend_priv *pnd_snd,
conn->tx_cdc_seq_fin = cdcpend->ctrl_seq;
}
- if (atomic_dec_and_test(&conn->cdc_pend_tx_wr) &&
- unlikely(wq_has_sleeper(&conn->cdc_pend_tx_wq)))
- wake_up(&conn->cdc_pend_tx_wq);
+ if (atomic_dec_and_test(&conn->cdc_pend_tx_wr)) {
+ /* If this is the last pending WR complete, we must push to
+ * prevent hang when autocork enabled.
+ */
+ smc_tx_sndbuf_nonempty(conn);
+ if (unlikely(wq_has_sleeper(&conn->cdc_pend_tx_wq)))
+ wake_up(&conn->cdc_pend_tx_wq);
+ }
WARN_ON(atomic_read(&conn->cdc_pend_tx_wr) < 0);
smc_tx_sndbuf_nonfull(smc);
diff --git a/net/smc/smc_tx.c b/net/smc/smc_tx.c
index 5df3940d4543..bc737ac79805 100644
--- a/net/smc/smc_tx.c
+++ b/net/smc/smc_tx.c
@@ -31,6 +31,7 @@
#include "smc_tracepoint.h"
#define SMC_TX_WORK_DELAY 0
+#define SMC_DEFAULT_AUTOCORK_SIZE (64 * 1024)
/***************************** sndbuf producer *******************************/
@@ -127,10 +128,52 @@ static int smc_tx_wait(struct smc_sock *smc, int flags)
static bool smc_tx_is_corked(struct smc_sock *smc)
{
struct tcp_sock *tp = tcp_sk(smc->clcsock->sk);
-
return (tp->nonagle & TCP_NAGLE_CORK) ? true : false;
}
+/* If we have pending CDC messages, do not send:
+ * Because CQE of this CDC message will happen shortly, it gives
+ * a chance to coalesce future sendmsg() payload in to one RDMA Write,
+ * without need for a timer, and with no latency trade off.
+ * Algorithm here:
+ * 1. First message should never cork
+ * 2. If we have pending CDC messages, wait for the first
+ * message's completion
+ * 3. Don't cork to much data in a single RDMA Write to prevent burst,
+ * total corked message should not exceed min(64k, sendbuf/2)
+ */
+static bool smc_should_autocork(struct smc_sock *smc, struct msghdr *msg,
+ int size_goal)
+{
+ struct smc_connection *conn = &smc->conn;
+
+ if (atomic_read(&conn->cdc_pend_tx_wr) == 0 ||
+ smc_tx_prepared_sends(conn) > min(size_goal,
+ conn->sndbuf_desc->len >> 1))
+ return false;
+ return true;
+}
+
+static bool smc_tx_should_cork(struct smc_sock *smc, struct msghdr *msg)
+{
+ struct smc_connection *conn = &smc->conn;
+
+ if (smc_should_autocork(smc, msg, SMC_DEFAULT_AUTOCORK_SIZE))
+ return true;
+
+ if ((msg->msg_flags & MSG_MORE ||
+ smc_tx_is_corked(smc) ||
+ msg->msg_flags & MSG_SENDPAGE_NOTLAST) &&
+ (atomic_read(&conn->sndbuf_space)))
+ /* for a corked socket defer the RDMA writes if
+ * sndbuf_space is still available. The applications
+ * should known how/when to uncork it.
+ */
+ return true;
+
+ return false;
+}
+
/* sndbuf producer: main API called by socket layer.
* called under sock lock.
*/
@@ -177,6 +220,13 @@ int smc_tx_sendmsg(struct smc_sock *smc, struct msghdr *msg, size_t len)
if (msg->msg_flags & MSG_OOB)
conn->local_tx_ctrl.prod_flags.urg_data_pending = 1;
+ /* If our send queue is full but peer have RMBE space,
+ * we should send them out before wait
+ */
+ if (!atomic_read(&conn->sndbuf_space) &&
+ atomic_read(&conn->peer_rmbe_space) > 0)
+ smc_tx_sndbuf_nonempty(conn);
+
if (!atomic_read(&conn->sndbuf_space) || conn->urg_tx_pend) {
if (send_done)
return send_done;
@@ -235,15 +285,12 @@ int smc_tx_sendmsg(struct smc_sock *smc, struct msghdr *msg, size_t len)
*/
if ((msg->msg_flags & MSG_OOB) && !send_remaining)
conn->urg_tx_pend = true;
- if ((msg->msg_flags & MSG_MORE || smc_tx_is_corked(smc) ||
- msg->msg_flags & MSG_SENDPAGE_NOTLAST) &&
- (atomic_read(&conn->sndbuf_space)))
- /* for a corked socket defer the RDMA writes if
- * sndbuf_space is still available. The applications
- * should known how/when to uncork it.
- */
- continue;
- smc_tx_sndbuf_nonempty(conn);
+
+ /* If we need to cork, do nothing and wait for the next
+ * sendmsg() call or push on tx completion
+ */
+ if (!smc_tx_should_cork(smc, msg))
+ smc_tx_sndbuf_nonempty(conn);
trace_smc_tx_sendmsg(smc, copylen);
} /* while (msg_data_left(msg)) */
@@ -590,13 +637,26 @@ static int smcd_tx_sndbuf_nonempty(struct smc_connection *conn)
return rc;
}
-int smc_tx_sndbuf_nonempty(struct smc_connection *conn)
+static int __smc_tx_sndbuf_nonempty(struct smc_connection *conn)
{
- int rc;
+ int rc = 0;
+ struct smc_sock *smc = container_of(conn, struct smc_sock, conn);
+
+ /* No data in the send queue */
+ if (unlikely(smc_tx_prepared_sends(conn) <= 0))
+ goto out;
+
+ /* Peer don't have RMBE space */
+ if (unlikely(atomic_read(&conn->peer_rmbe_space) <= 0)) {
+ SMC_STAT_RMB_TX_PEER_FULL(smc, !conn->lnk);
+ goto out;
+ }
if (conn->killed ||
- conn->local_rx_ctrl.conn_state_flags.peer_conn_abort)
- return -EPIPE; /* connection being aborted */
+ conn->local_rx_ctrl.conn_state_flags.peer_conn_abort) {
+ rc = -EPIPE; /* connection being aborted */
+ goto out;
+ }
if (conn->lgr->is_smcd)
rc = smcd_tx_sndbuf_nonempty(conn);
else
@@ -608,6 +668,36 @@ int smc_tx_sndbuf_nonempty(struct smc_connection *conn)
conn);
smc_close_wake_tx_prepared(smc);
}
+
+out:
+ return rc;
+}
+
+int smc_tx_sndbuf_nonempty(struct smc_connection *conn)
+{
+ int rc;
+
+ /* This make sure only one can send simultaneously to prevent wasting
+ * of CPU and CDC slot.
+ * Record whether someone has tried to push while we are pushing.
+ */
+ if (atomic_inc_return(&conn->tx_pushing) > 1)
+ return 0;
+
+again:
+ atomic_set(&conn->tx_pushing, 1);
+ smp_wmb(); /* Make sure tx_pushing is 1 before real send */
+ rc = __smc_tx_sndbuf_nonempty(conn);
+
+ /* We need to check whether someone else have added some data into
+ * the send queue and tried to push but failed after the atomic_set()
+ * when we are pushing.
+ * If so, we need to push again to prevent those data hang in the send
+ * queue.
+ */
+ if (unlikely(!atomic_dec_and_test(&conn->tx_pushing)))
+ goto again;
+
return rc;
}
--
2.19.1.3.ge56e4f7
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