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Message-ID: <6e9c637c-50b0-394c-f405-8b98deafa2ef@linux.ibm.com>
Date: Wed, 16 Feb 2022 11:32:52 +0100
From: Karsten Graul <kgraul@...ux.ibm.com>
To: Dust Li <dust.li@...ux.alibaba.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: Re: [PATCH] net/smc: Add autocork support
On 16/02/2022 04:49, Dust Li wrote:
> 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:
Sounds like a valuable improvement, thank you!
> ---
> 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 */
> +
Is this extra empty line needed?
> 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);
Reverse Christmas tree style please.
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