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Message-ID: <20220216105538.GA54562@linux.alibaba.com>
Date: Wed, 16 Feb 2022 18:55:38 +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: Re: [PATCH] net/smc: Add autocork support
On Wed, Feb 16, 2022 at 11:32:52AM +0100, Karsten Graul wrote:
>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?
Will remove this empty line in the next version.
>
>> 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.
Sure, will do.
Thank you !
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