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Message-ID: <faf616cf-ea40-153e-bc42-a50b418e9ed9@gmail.com>
Date:   Fri, 9 Sep 2022 14:39:24 -0500
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Subject: Re: [RFC PATCH 2/7] RDMA/rxe: Convert the triple tasklets to
 workqueues
Content-Language: en-US
To:     Daisuke Matsuda <matsuda-daisuke@fujitsu.com>,
        linux-rdma@vger.kernel.org, leonro@nvidia.com, jgg@nvidia.com,
        zyjzyj2000@gmail.com, "Ziemba, Ian" <ian.ziemba@hpe.com>,
        Frank Zago <frank.zago@hpe.com>
Cc:     nvdimm@lists.linux.dev, linux-kernel@vger.kernel.org,
        yangx.jy@fujitsu.com, lizhijian@fujitsu.com, y-goto@fujitsu.com
References: <cover.1662461897.git.matsuda-daisuke@fujitsu.com>
 <41e5476f4f14a0b77f4a8c3826e3ef943bf7c173.1662461897.git.matsuda-daisuke@fujitsu.com>
From:   Bob Pearson <rpearsonhpe@gmail.com>
In-Reply-To: <41e5476f4f14a0b77f4a8c3826e3ef943bf7c173.1662461897.git.matsuda-daisuke@fujitsu.com>
Content-Type: text/plain; charset=UTF-8
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Precedence: bulk

On 9/6/22 21:43, Daisuke Matsuda wrote:
> In order to implement On-Demand Paging on the rxe driver, triple tasklets
> (requester, responder, and completer) must be allowed to sleep so that they
> can trigger page fault when pages being accessed are not present.
> 
> This patch replaces the tasklets with workqueues, but still allows direct-
> call of works from softirq context if it is obvious that MRs are not going
> to be accessed and there is no work being processed in the workqueue.
> 
> As counterparts to tasklet_disable() and tasklet_enable() are missing for
> workqueues, an atomic value is introduced to get works suspended while qp
> reset is in progress.
> 
> As a reference, performance change was measured using ib_send_bw and
> ib_send_lat commands over RC connection. Both the client and the server
> were placed on the same KVM host. An option "-n 100000" was given to the
> respective commands to iterate over 100000 times.
> 
> Before applying this patch:
> [ib_send_bw]
> ---------------------------------------------------------------------------------------
>  #bytes     #iterations    BW peak[MB/sec]    BW average[MB/sec]   MsgRate[Mpps]
>  65536      100000           0.00               203.13             0.003250
> ---------------------------------------------------------------------------------------
> [ib_send_lat]
> ---------------------------------------------------------------------------------------
>  #bytes #iterations    t_min[usec]    t_max[usec]  t_typical[usec]    t_avg[usec]    t_stdev[usec]   99% percentile[usec]   99.9% percentile[usec]
>  2       100000          30.91          1519.05      34.23             36.06            5.15            48.49                   82.37
> ---------------------------------------------------------------------------------------
> 
> After applying this patch:
> [ib_send_bw]
> ---------------------------------------------------------------------------------------
>  #bytes     #iterations    BW peak[MB/sec]    BW average[MB/sec]   MsgRate[Mpps]
>  65536      100000           0.00               240.88             0.003854
> ---------------------------------------------------------------------------------------
> [ib_send_lat]
> ---------------------------------------------------------------------------------------
>  #bytes #iterations    t_min[usec]    t_max[usec]  t_typical[usec]    t_avg[usec]    t_stdev[usec]   99% percentile[usec]   99.9% percentile[usec]
>  2       100000          40.88          2994.82      47.80             50.25            13.70           76.42                   185.04
> ---------------------------------------------------------------------------------------
> 
> The test was conducted 3 times for each kernel, and the results with median
> "BW average" and "t_typical" are shown above. It shows the conversion
> improves the bandwidth while causing higher latency.
> 
> Signed-off-by: Daisuke Matsuda <matsuda-daisuke@fujitsu.com>
> ---
>  drivers/infiniband/sw/rxe/Makefile    |   2 +-
>  drivers/infiniband/sw/rxe/rxe_comp.c  |  42 ++++---
>  drivers/infiniband/sw/rxe/rxe_loc.h   |   2 +-
>  drivers/infiniband/sw/rxe/rxe_net.c   |   4 +-
>  drivers/infiniband/sw/rxe/rxe_param.h |   2 +-
>  drivers/infiniband/sw/rxe/rxe_qp.c    |  68 +++++------
>  drivers/infiniband/sw/rxe/rxe_recv.c  |   2 +-
>  drivers/infiniband/sw/rxe/rxe_req.c   |  14 +--
>  drivers/infiniband/sw/rxe/rxe_resp.c  |  16 +--
>  drivers/infiniband/sw/rxe/rxe_task.c  | 152 ------------------------
>  drivers/infiniband/sw/rxe/rxe_task.h  |  69 -----------
>  drivers/infiniband/sw/rxe/rxe_verbs.c |   8 +-
>  drivers/infiniband/sw/rxe/rxe_verbs.h |   8 +-
>  drivers/infiniband/sw/rxe/rxe_wq.c    | 161 ++++++++++++++++++++++++++
>  drivers/infiniband/sw/rxe/rxe_wq.h    |  71 ++++++++++++
>  15 files changed, 322 insertions(+), 299 deletions(-)
>  delete mode 100644 drivers/infiniband/sw/rxe/rxe_task.c
>  delete mode 100644 drivers/infiniband/sw/rxe/rxe_task.h
>  create mode 100644 drivers/infiniband/sw/rxe/rxe_wq.c
>  create mode 100644 drivers/infiniband/sw/rxe/rxe_wq.h
> 
> diff --git a/drivers/infiniband/sw/rxe/Makefile b/drivers/infiniband/sw/rxe/Makefile
> index 5395a581f4bb..358f6b06aa64 100644
> --- a/drivers/infiniband/sw/rxe/Makefile
> +++ b/drivers/infiniband/sw/rxe/Makefile
> @@ -20,6 +20,6 @@ rdma_rxe-y := \
>  	rxe_mmap.o \
>  	rxe_icrc.o \
>  	rxe_mcast.o \
> -	rxe_task.o \
> +	rxe_wq.o \
>  	rxe_net.o \
>  	rxe_hw_counters.o
> diff --git a/drivers/infiniband/sw/rxe/rxe_comp.c b/drivers/infiniband/sw/rxe/rxe_comp.c
> index fb0c008af78c..0348da06c4dd 100644
> --- a/drivers/infiniband/sw/rxe/rxe_comp.c
> +++ b/drivers/infiniband/sw/rxe/rxe_comp.c
> @@ -9,7 +9,7 @@
>  #include "rxe.h"
>  #include "rxe_loc.h"
>  #include "rxe_queue.h"
> -#include "rxe_task.h"
> +#include "rxe_wq.h"
>  
>  enum comp_state {
>  	COMPST_GET_ACK,
> @@ -118,21 +118,37 @@ void retransmit_timer(struct timer_list *t)
>  
>  	if (qp->valid) {
>  		qp->comp.timeout = 1;
> -		rxe_run_task(&qp->comp.task, 1);
> +		rxe_run_work(&qp->comp.work, 1);
>  	}
>  }
>  
> -void rxe_comp_queue_pkt(struct rxe_qp *qp, struct sk_buff *skb)
> +void rxe_comp_queue_pkt(struct rxe_pkt_info *pkt, struct sk_buff *skb)
>  {
> +	struct rxe_qp *qp = pkt->qp;
>  	int must_sched;
>  
>  	skb_queue_tail(&qp->resp_pkts, skb);
>  
> -	must_sched = skb_queue_len(&qp->resp_pkts) > 1;
> +	/* Schedule a workqueue when processing READ and ATOMIC acks.
> +	 * In these cases, completer may sleep to access ODP-enabled MRs.
> +	 */
> +	switch (pkt->opcode) {
> +	case IB_OPCODE_RC_RDMA_READ_RESPONSE_FIRST:
> +	case IB_OPCODE_RC_RDMA_READ_RESPONSE_LAST:
> +	case IB_OPCODE_RC_RDMA_READ_RESPONSE_ONLY:
> +	case IB_OPCODE_RC_RDMA_READ_RESPONSE_MIDDLE:
> +	case IB_OPCODE_RC_ATOMIC_ACKNOWLEDGE:
> +		must_sched = 1;
> +		break;
> +
> +	default:
> +		must_sched = skb_queue_len(&qp->resp_pkts) > 1;
> +	}
> +
>  	if (must_sched != 0)
>  		rxe_counter_inc(SKB_TO_PKT(skb)->rxe, RXE_CNT_COMPLETER_SCHED);
>  
> -	rxe_run_task(&qp->comp.task, must_sched);
> +	rxe_run_work(&qp->comp.work, must_sched);
>  }
>  
>  static inline enum comp_state get_wqe(struct rxe_qp *qp,
> @@ -305,7 +321,7 @@ static inline enum comp_state check_ack(struct rxe_qp *qp,
>  					qp->comp.psn = pkt->psn;
>  					if (qp->req.wait_psn) {
>  						qp->req.wait_psn = 0;
> -						rxe_run_task(&qp->req.task, 0);
> +						rxe_run_work(&qp->req.work, 0);
>  					}
>  				}
>  				return COMPST_ERROR_RETRY;
> @@ -452,7 +468,7 @@ static void do_complete(struct rxe_qp *qp, struct rxe_send_wqe *wqe)
>  	 */
>  	if (qp->req.wait_fence) {
>  		qp->req.wait_fence = 0;
> -		rxe_run_task(&qp->req.task, 0);
> +		rxe_run_work(&qp->req.work, 0);
>  	}
>  }
>  
> @@ -466,7 +482,7 @@ static inline enum comp_state complete_ack(struct rxe_qp *qp,
>  		if (qp->req.need_rd_atomic) {
>  			qp->comp.timeout_retry = 0;
>  			qp->req.need_rd_atomic = 0;
> -			rxe_run_task(&qp->req.task, 0);
> +			rxe_run_work(&qp->req.work, 0);
>  		}
>  	}
>  
> @@ -512,7 +528,7 @@ static inline enum comp_state complete_wqe(struct rxe_qp *qp,
>  
>  		if (qp->req.wait_psn) {
>  			qp->req.wait_psn = 0;
> -			rxe_run_task(&qp->req.task, 1);
> +			rxe_run_work(&qp->req.work, 1);
>  		}
>  	}
>  
> @@ -646,7 +662,7 @@ int rxe_completer(void *arg)
>  
>  			if (qp->req.wait_psn) {
>  				qp->req.wait_psn = 0;
> -				rxe_run_task(&qp->req.task, 1);
> +				rxe_run_work(&qp->req.work, 1);
>  			}
>  
>  			state = COMPST_DONE;
> @@ -714,7 +730,7 @@ int rxe_completer(void *arg)
>  							RXE_CNT_COMP_RETRY);
>  					qp->req.need_retry = 1;
>  					qp->comp.started_retry = 1;
> -					rxe_run_task(&qp->req.task, 0);
> +					rxe_run_work(&qp->req.work, 0);
>  				}
>  				goto done;
>  
> @@ -757,8 +773,8 @@ int rxe_completer(void *arg)
>  		}
>  	}
>  
> -	/* A non-zero return value will cause rxe_do_task to
> -	 * exit its loop and end the tasklet. A zero return
> +	/* A non-zero return value will cause rxe_do_work to
> +	 * exit its loop and end the work. A zero return
>  	 * will continue looping and return to rxe_completer
>  	 */
>  done:
> diff --git a/drivers/infiniband/sw/rxe/rxe_loc.h b/drivers/infiniband/sw/rxe/rxe_loc.h
> index 22f6cc31d1d6..0f8cb9e38cc9 100644
> --- a/drivers/infiniband/sw/rxe/rxe_loc.h
> +++ b/drivers/infiniband/sw/rxe/rxe_loc.h
> @@ -181,7 +181,7 @@ void rxe_icrc_generate(struct sk_buff *skb, struct rxe_pkt_info *pkt);
>  
>  void rxe_resp_queue_pkt(struct rxe_qp *qp, struct sk_buff *skb);
>  
> -void rxe_comp_queue_pkt(struct rxe_qp *qp, struct sk_buff *skb);
> +void rxe_comp_queue_pkt(struct rxe_pkt_info *pkt, struct sk_buff *skb);
>  
>  static inline unsigned int wr_opcode_mask(int opcode, struct rxe_qp *qp)
>  {
> diff --git a/drivers/infiniband/sw/rxe/rxe_net.c b/drivers/infiniband/sw/rxe/rxe_net.c
> index c53f4529f098..5526970882c8 100644
> --- a/drivers/infiniband/sw/rxe/rxe_net.c
> +++ b/drivers/infiniband/sw/rxe/rxe_net.c
> @@ -346,7 +346,7 @@ static void rxe_skb_tx_dtor(struct sk_buff *skb)
>  
>  	if (unlikely(qp->need_req_skb &&
>  		     skb_out < RXE_INFLIGHT_SKBS_PER_QP_LOW))
> -		rxe_run_task(&qp->req.task, 1);
> +		rxe_run_work(&qp->req.work, 1);
>  
>  	rxe_put(qp);
>  }
> @@ -430,7 +430,7 @@ int rxe_xmit_packet(struct rxe_qp *qp, struct rxe_pkt_info *pkt,
>  	if ((qp_type(qp) != IB_QPT_RC) &&
>  	    (pkt->mask & RXE_END_MASK)) {
>  		pkt->wqe->state = wqe_state_done;
> -		rxe_run_task(&qp->comp.task, 1);
> +		rxe_run_work(&qp->comp.work, 1);
>  	}
>  
>  	rxe_counter_inc(rxe, RXE_CNT_SENT_PKTS);
> diff --git a/drivers/infiniband/sw/rxe/rxe_param.h b/drivers/infiniband/sw/rxe/rxe_param.h
> index 86c7a8bf3cbb..1c0251812fc8 100644
> --- a/drivers/infiniband/sw/rxe/rxe_param.h
> +++ b/drivers/infiniband/sw/rxe/rxe_param.h
> @@ -105,7 +105,7 @@ enum rxe_device_param {
>  	RXE_INFLIGHT_SKBS_PER_QP_HIGH	= 64,
>  	RXE_INFLIGHT_SKBS_PER_QP_LOW	= 16,
>  
> -	/* Max number of interations of each tasklet
> +	/* Max number of interations of each work
>  	 * before yielding the cpu to let other
>  	 * work make progress
>  	 */
> diff --git a/drivers/infiniband/sw/rxe/rxe_qp.c b/drivers/infiniband/sw/rxe/rxe_qp.c
> index 516bf9b95e48..c7c7acd4ecfa 100644
> --- a/drivers/infiniband/sw/rxe/rxe_qp.c
> +++ b/drivers/infiniband/sw/rxe/rxe_qp.c
> @@ -13,7 +13,7 @@
>  #include "rxe.h"
>  #include "rxe_loc.h"
>  #include "rxe_queue.h"
> -#include "rxe_task.h"
> +#include "rxe_wq.h"
>  
>  static int rxe_qp_chk_cap(struct rxe_dev *rxe, struct ib_qp_cap *cap,
>  			  int has_srq)
> @@ -172,9 +172,9 @@ static void rxe_qp_init_misc(struct rxe_dev *rxe, struct rxe_qp *qp,
>  
>  	spin_lock_init(&qp->state_lock);
>  
> -	spin_lock_init(&qp->req.task.state_lock);
> -	spin_lock_init(&qp->resp.task.state_lock);
> -	spin_lock_init(&qp->comp.task.state_lock);
> +	spin_lock_init(&qp->req.work.state_lock);
> +	spin_lock_init(&qp->resp.work.state_lock);
> +	spin_lock_init(&qp->comp.work.state_lock);
>  
>  	spin_lock_init(&qp->sq.sq_lock);
>  	spin_lock_init(&qp->rq.producer_lock);
> @@ -242,10 +242,10 @@ static int rxe_qp_init_req(struct rxe_dev *rxe, struct rxe_qp *qp,
>  
>  	skb_queue_head_init(&qp->req_pkts);
>  
> -	rxe_init_task(rxe, &qp->req.task, qp,
> -		      rxe_requester, "req");
> -	rxe_init_task(rxe, &qp->comp.task, qp,
> -		      rxe_completer, "comp");
> +	rxe_init_work(rxe, &qp->req.work, qp,
> +		      rxe_requester, "rxe_req");
> +	rxe_init_work(rxe, &qp->comp.work, qp,
> +		      rxe_completer, "rxe_comp");
>  
>  	qp->qp_timeout_jiffies = 0; /* Can't be set for UD/UC in modify_qp */
>  	if (init->qp_type == IB_QPT_RC) {
> @@ -292,8 +292,8 @@ static int rxe_qp_init_resp(struct rxe_dev *rxe, struct rxe_qp *qp,
>  
>  	skb_queue_head_init(&qp->resp_pkts);
>  
> -	rxe_init_task(rxe, &qp->resp.task, qp,
> -		      rxe_responder, "resp");
> +	rxe_init_work(rxe, &qp->resp.work, qp,
> +		      rxe_responder, "rxe_resp");
>  
>  	qp->resp.opcode		= OPCODE_NONE;
>  	qp->resp.msn		= 0;
> @@ -481,14 +481,14 @@ int rxe_qp_chk_attr(struct rxe_dev *rxe, struct rxe_qp *qp,
>  /* move the qp to the reset state */
>  static void rxe_qp_reset(struct rxe_qp *qp)
>  {
> -	/* stop tasks from running */
> -	rxe_disable_task(&qp->resp.task);
> +	/* flush workqueue and stop works from running */
> +	rxe_disable_work(&qp->resp.work);
>  
>  	/* stop request/comp */
>  	if (qp->sq.queue) {
>  		if (qp_type(qp) == IB_QPT_RC)
> -			rxe_disable_task(&qp->comp.task);
> -		rxe_disable_task(&qp->req.task);
> +			rxe_disable_work(&qp->comp.work);
> +		rxe_disable_work(&qp->req.work);
>  	}
>  
>  	/* move qp to the reset state */
> @@ -499,11 +499,11 @@ static void rxe_qp_reset(struct rxe_qp *qp)
>  	/* let state machines reset themselves drain work and packet queues
>  	 * etc.
>  	 */
> -	__rxe_do_task(&qp->resp.task);
> +	__rxe_do_work(&qp->resp.work);
>  
>  	if (qp->sq.queue) {
> -		__rxe_do_task(&qp->comp.task);
> -		__rxe_do_task(&qp->req.task);
> +		__rxe_do_work(&qp->comp.work);
> +		__rxe_do_work(&qp->req.work);
>  		rxe_queue_reset(qp->sq.queue);
>  	}
>  
> @@ -526,14 +526,14 @@ static void rxe_qp_reset(struct rxe_qp *qp)
>  
>  	cleanup_rd_atomic_resources(qp);
>  
> -	/* reenable tasks */
> -	rxe_enable_task(&qp->resp.task);
> +	/* reenable workqueue */
> +	rxe_enable_work(&qp->resp.work);
>  
>  	if (qp->sq.queue) {
>  		if (qp_type(qp) == IB_QPT_RC)
> -			rxe_enable_task(&qp->comp.task);
> +			rxe_enable_work(&qp->comp.work);
>  
> -		rxe_enable_task(&qp->req.task);
> +		rxe_enable_work(&qp->req.work);
>  	}
>  }
>  
> @@ -544,10 +544,10 @@ static void rxe_qp_drain(struct rxe_qp *qp)
>  		if (qp->req.state != QP_STATE_DRAINED) {
>  			qp->req.state = QP_STATE_DRAIN;
>  			if (qp_type(qp) == IB_QPT_RC)
> -				rxe_run_task(&qp->comp.task, 1);
> +				rxe_run_work(&qp->comp.work, 1);
>  			else
> -				__rxe_do_task(&qp->comp.task);
> -			rxe_run_task(&qp->req.task, 1);
> +				__rxe_do_work(&qp->comp.work);
> +			rxe_run_work(&qp->req.work, 1);
>  		}
>  	}
>  }
> @@ -561,13 +561,13 @@ void rxe_qp_error(struct rxe_qp *qp)
>  	qp->attr.qp_state = IB_QPS_ERR;
>  
>  	/* drain work and packet queues */
> -	rxe_run_task(&qp->resp.task, 1);
> +	rxe_run_work(&qp->resp.work, 1);
>  
>  	if (qp_type(qp) == IB_QPT_RC)
> -		rxe_run_task(&qp->comp.task, 1);
> +		rxe_run_work(&qp->comp.work, 1);
>  	else
> -		__rxe_do_task(&qp->comp.task);
> -	rxe_run_task(&qp->req.task, 1);
> +		__rxe_do_work(&qp->comp.work);
> +	rxe_run_work(&qp->req.work, 1);
>  }
>  
>  /* called by the modify qp verb */
> @@ -786,21 +786,21 @@ static void rxe_qp_do_cleanup(struct work_struct *work)
>  
>  	qp->valid = 0;
>  	qp->qp_timeout_jiffies = 0;
> -	rxe_cleanup_task(&qp->resp.task);
> +	rxe_cleanup_work(&qp->resp.work);
>  
>  	if (qp_type(qp) == IB_QPT_RC) {
>  		del_timer_sync(&qp->retrans_timer);
>  		del_timer_sync(&qp->rnr_nak_timer);
>  	}
>  
> -	rxe_cleanup_task(&qp->req.task);
> -	rxe_cleanup_task(&qp->comp.task);
> +	rxe_cleanup_work(&qp->req.work);
> +	rxe_cleanup_work(&qp->comp.work);
>  
>  	/* flush out any receive wr's or pending requests */
> -	__rxe_do_task(&qp->req.task);
> +	__rxe_do_work(&qp->req.work);
>  	if (qp->sq.queue) {
> -		__rxe_do_task(&qp->comp.task);
> -		__rxe_do_task(&qp->req.task);
> +		__rxe_do_work(&qp->comp.work);
> +		__rxe_do_work(&qp->req.work);
>  	}
>  
>  	if (qp->sq.queue)
> diff --git a/drivers/infiniband/sw/rxe/rxe_recv.c b/drivers/infiniband/sw/rxe/rxe_recv.c
> index f3ad7b6dbd97..3b525e9d903e 100644
> --- a/drivers/infiniband/sw/rxe/rxe_recv.c
> +++ b/drivers/infiniband/sw/rxe/rxe_recv.c
> @@ -226,7 +226,7 @@ static inline void rxe_rcv_pkt(struct rxe_pkt_info *pkt, struct sk_buff *skb)
>  	if (pkt->mask & RXE_REQ_MASK)
>  		rxe_resp_queue_pkt(pkt->qp, skb);
>  	else
> -		rxe_comp_queue_pkt(pkt->qp, skb);
> +		rxe_comp_queue_pkt(pkt, skb);
>  }
>  
>  static void rxe_rcv_mcast_pkt(struct rxe_dev *rxe, struct sk_buff *skb)
> diff --git a/drivers/infiniband/sw/rxe/rxe_req.c b/drivers/infiniband/sw/rxe/rxe_req.c
> index f63771207970..bd05dd3de499 100644
> --- a/drivers/infiniband/sw/rxe/rxe_req.c
> +++ b/drivers/infiniband/sw/rxe/rxe_req.c
> @@ -105,7 +105,7 @@ void rnr_nak_timer(struct timer_list *t)
>  	/* request a send queue retry */
>  	qp->req.need_retry = 1;
>  	qp->req.wait_for_rnr_timer = 0;
> -	rxe_run_task(&qp->req.task, 1);
> +	rxe_run_work(&qp->req.work, 1);
>  }
>  
>  static struct rxe_send_wqe *req_next_wqe(struct rxe_qp *qp)
> @@ -608,7 +608,7 @@ static int rxe_do_local_ops(struct rxe_qp *qp, struct rxe_send_wqe *wqe)
>  	 * which can lead to a deadlock. So go ahead and complete
>  	 * it now.
>  	 */
> -	rxe_run_task(&qp->comp.task, 1);
> +	rxe_run_work(&qp->comp.work, 1);
>  
>  	return 0;
>  }
> @@ -733,7 +733,7 @@ int rxe_requester(void *arg)
>  						       qp->req.wqe_index);
>  			wqe->state = wqe_state_done;
>  			wqe->status = IB_WC_SUCCESS;
> -			rxe_run_task(&qp->comp.task, 0);
> +			rxe_run_work(&qp->comp.work, 0);
>  			goto done;
>  		}
>  		payload = mtu;
> @@ -795,7 +795,7 @@ int rxe_requester(void *arg)
>  		rollback_state(wqe, qp, &rollback_wqe, rollback_psn);
>  
>  		if (err == -EAGAIN) {
> -			rxe_run_task(&qp->req.task, 1);
> +			rxe_run_work(&qp->req.work, 1);
>  			goto exit;
>  		}
>  
> @@ -805,8 +805,8 @@ int rxe_requester(void *arg)
>  
>  	update_state(qp, &pkt);
>  
> -	/* A non-zero return value will cause rxe_do_task to
> -	 * exit its loop and end the tasklet. A zero return
> +	/* A non-zero return value will cause rxe_do_work to
> +	 * exit its loop and end the work. A zero return
>  	 * will continue looping and return to rxe_requester
>  	 */
>  done:
> @@ -817,7 +817,7 @@ int rxe_requester(void *arg)
>  	qp->req.wqe_index = queue_next_index(qp->sq.queue, qp->req.wqe_index);
>  	wqe->state = wqe_state_error;
>  	qp->req.state = QP_STATE_ERROR;
> -	rxe_run_task(&qp->comp.task, 0);
> +	rxe_run_work(&qp->comp.work, 0);
>  exit:
>  	ret = -EAGAIN;
>  out:
> diff --git a/drivers/infiniband/sw/rxe/rxe_resp.c b/drivers/infiniband/sw/rxe/rxe_resp.c
> index b36ec5c4d5e0..e97c55b292f0 100644
> --- a/drivers/infiniband/sw/rxe/rxe_resp.c
> +++ b/drivers/infiniband/sw/rxe/rxe_resp.c
> @@ -83,15 +83,11 @@ static char *resp_state_name[] = {
>  /* rxe_recv calls here to add a request packet to the input queue */
>  void rxe_resp_queue_pkt(struct rxe_qp *qp, struct sk_buff *skb)
>  {
> -	int must_sched;
> -	struct rxe_pkt_info *pkt = SKB_TO_PKT(skb);
> -
> +	/* responder can sleep to access ODP-enabled MRs, so schedule the
> +	 * workqueue for all incoming requests.
> +	 */
>  	skb_queue_tail(&qp->req_pkts, skb);
> -
> -	must_sched = (pkt->opcode == IB_OPCODE_RC_RDMA_READ_REQUEST) ||
> -			(skb_queue_len(&qp->req_pkts) > 1);
> -
> -	rxe_run_task(&qp->resp.task, must_sched);
> +	rxe_run_work(&qp->resp.work, 1);
>  }
>  
>  static inline enum resp_states get_req(struct rxe_qp *qp,
> @@ -1464,8 +1460,8 @@ int rxe_responder(void *arg)
>  		}
>  	}
>  
> -	/* A non-zero return value will cause rxe_do_task to
> -	 * exit its loop and end the tasklet. A zero return
> +	/* A non-zero return value will cause rxe_do_work to
> +	 * exit its loop and end the work. A zero return
>  	 * will continue looping and return to rxe_responder
>  	 */
>  done:
> diff --git a/drivers/infiniband/sw/rxe/rxe_task.c b/drivers/infiniband/sw/rxe/rxe_task.c
> deleted file mode 100644
> index 2248cf33d776..000000000000
> --- a/drivers/infiniband/sw/rxe/rxe_task.c
> +++ /dev/null
> @@ -1,152 +0,0 @@
> -// SPDX-License-Identifier: GPL-2.0 OR Linux-OpenIB
> -/*
> - * Copyright (c) 2016 Mellanox Technologies Ltd. All rights reserved.
> - * Copyright (c) 2015 System Fabric Works, Inc. All rights reserved.
> - */
> -
> -#include <linux/kernel.h>
> -#include <linux/interrupt.h>
> -#include <linux/hardirq.h>
> -
> -#include "rxe.h"
> -
> -int __rxe_do_task(struct rxe_task *task)
> -
> -{
> -	int ret;
> -
> -	while ((ret = task->func(task->arg)) == 0)
> -		;
> -
> -	task->ret = ret;
> -
> -	return ret;
> -}
> -
> -/*
> - * this locking is due to a potential race where
> - * a second caller finds the task already running
> - * but looks just after the last call to func
> - */
> -void rxe_do_task(struct tasklet_struct *t)
> -{
> -	int cont;
> -	int ret;
> -	struct rxe_task *task = from_tasklet(task, t, tasklet);
> -	unsigned int iterations = RXE_MAX_ITERATIONS;
> -
> -	spin_lock_bh(&task->state_lock);
> -	switch (task->state) {
> -	case TASK_STATE_START:
> -		task->state = TASK_STATE_BUSY;
> -		spin_unlock_bh(&task->state_lock);
> -		break;
> -
> -	case TASK_STATE_BUSY:
> -		task->state = TASK_STATE_ARMED;
> -		fallthrough;
> -	case TASK_STATE_ARMED:
> -		spin_unlock_bh(&task->state_lock);
> -		return;
> -
> -	default:
> -		spin_unlock_bh(&task->state_lock);
> -		pr_warn("%s failed with bad state %d\n", __func__, task->state);
> -		return;
> -	}
> -
> -	do {
> -		cont = 0;
> -		ret = task->func(task->arg);
> -
> -		spin_lock_bh(&task->state_lock);
> -		switch (task->state) {
> -		case TASK_STATE_BUSY:
> -			if (ret) {
> -				task->state = TASK_STATE_START;
> -			} else if (iterations--) {
> -				cont = 1;
> -			} else {
> -				/* reschedule the tasklet and exit
> -				 * the loop to give up the cpu
> -				 */
> -				tasklet_schedule(&task->tasklet);
> -				task->state = TASK_STATE_START;
> -			}
> -			break;
> -
> -		/* someone tried to run the task since the last time we called
> -		 * func, so we will call one more time regardless of the
> -		 * return value
> -		 */
> -		case TASK_STATE_ARMED:
> -			task->state = TASK_STATE_BUSY;
> -			cont = 1;
> -			break;
> -
> -		default:
> -			pr_warn("%s failed with bad state %d\n", __func__,
> -				task->state);
> -		}
> -		spin_unlock_bh(&task->state_lock);
> -	} while (cont);
> -
> -	task->ret = ret;
> -}
> -
> -int rxe_init_task(void *obj, struct rxe_task *task,
> -		  void *arg, int (*func)(void *), char *name)
> -{
> -	task->obj	= obj;
> -	task->arg	= arg;
> -	task->func	= func;
> -	snprintf(task->name, sizeof(task->name), "%s", name);
> -	task->destroyed	= false;
> -
> -	tasklet_setup(&task->tasklet, rxe_do_task);
> -
> -	task->state = TASK_STATE_START;
> -	spin_lock_init(&task->state_lock);
> -
> -	return 0;
> -}
> -
> -void rxe_cleanup_task(struct rxe_task *task)
> -{
> -	bool idle;
> -
> -	/*
> -	 * Mark the task, then wait for it to finish. It might be
> -	 * running in a non-tasklet (direct call) context.
> -	 */
> -	task->destroyed = true;
> -
> -	do {
> -		spin_lock_bh(&task->state_lock);
> -		idle = (task->state == TASK_STATE_START);
> -		spin_unlock_bh(&task->state_lock);
> -	} while (!idle);
> -
> -	tasklet_kill(&task->tasklet);
> -}
> -
> -void rxe_run_task(struct rxe_task *task, int sched)
> -{
> -	if (task->destroyed)
> -		return;
> -
> -	if (sched)
> -		tasklet_schedule(&task->tasklet);
> -	else
> -		rxe_do_task(&task->tasklet);
> -}
> -
> -void rxe_disable_task(struct rxe_task *task)
> -{
> -	tasklet_disable(&task->tasklet);
> -}
> -
> -void rxe_enable_task(struct rxe_task *task)
> -{
> -	tasklet_enable(&task->tasklet);
> -}
> diff --git a/drivers/infiniband/sw/rxe/rxe_task.h b/drivers/infiniband/sw/rxe/rxe_task.h
> deleted file mode 100644
> index 11d183fd3338..000000000000
> --- a/drivers/infiniband/sw/rxe/rxe_task.h
> +++ /dev/null
> @@ -1,69 +0,0 @@
> -/* SPDX-License-Identifier: GPL-2.0 OR Linux-OpenIB */
> -/*
> - * Copyright (c) 2016 Mellanox Technologies Ltd. All rights reserved.
> - * Copyright (c) 2015 System Fabric Works, Inc. All rights reserved.
> - */
> -
> -#ifndef RXE_TASK_H
> -#define RXE_TASK_H
> -
> -enum {
> -	TASK_STATE_START	= 0,
> -	TASK_STATE_BUSY		= 1,
> -	TASK_STATE_ARMED	= 2,
> -};
> -
> -/*
> - * data structure to describe a 'task' which is a short
> - * function that returns 0 as long as it needs to be
> - * called again.
> - */
> -struct rxe_task {
> -	void			*obj;
> -	struct tasklet_struct	tasklet;
> -	int			state;
> -	spinlock_t		state_lock; /* spinlock for task state */
> -	void			*arg;
> -	int			(*func)(void *arg);
> -	int			ret;
> -	char			name[16];
> -	bool			destroyed;
> -};
> -
> -/*
> - * init rxe_task structure
> - *	arg  => parameter to pass to fcn
> - *	func => function to call until it returns != 0
> - */
> -int rxe_init_task(void *obj, struct rxe_task *task,
> -		  void *arg, int (*func)(void *), char *name);
> -
> -/* cleanup task */
> -void rxe_cleanup_task(struct rxe_task *task);
> -
> -/*
> - * raw call to func in loop without any checking
> - * can call when tasklets are disabled
> - */
> -int __rxe_do_task(struct rxe_task *task);
> -
> -/*
> - * common function called by any of the main tasklets
> - * If there is any chance that there is additional
> - * work to do someone must reschedule the task before
> - * leaving
> - */
> -void rxe_do_task(struct tasklet_struct *t);
> -
> -/* run a task, else schedule it to run as a tasklet, The decision
> - * to run or schedule tasklet is based on the parameter sched.
> - */
> -void rxe_run_task(struct rxe_task *task, int sched);
> -
> -/* keep a task from scheduling */
> -void rxe_disable_task(struct rxe_task *task);
> -
> -/* allow task to run */
> -void rxe_enable_task(struct rxe_task *task);
> -
> -#endif /* RXE_TASK_H */
> diff --git a/drivers/infiniband/sw/rxe/rxe_verbs.c b/drivers/infiniband/sw/rxe/rxe_verbs.c
> index 9ebe9decad34..7510f25c5ea3 100644
> --- a/drivers/infiniband/sw/rxe/rxe_verbs.c
> +++ b/drivers/infiniband/sw/rxe/rxe_verbs.c
> @@ -697,9 +697,9 @@ static int rxe_post_send_kernel(struct rxe_qp *qp, const struct ib_send_wr *wr,
>  		wr = next;
>  	}
>  
> -	rxe_run_task(&qp->req.task, 1);
> +	rxe_run_work(&qp->req.work, 1);
>  	if (unlikely(qp->req.state == QP_STATE_ERROR))
> -		rxe_run_task(&qp->comp.task, 1);
> +		rxe_run_work(&qp->comp.work, 1);
>  
>  	return err;
>  }
> @@ -721,7 +721,7 @@ static int rxe_post_send(struct ib_qp *ibqp, const struct ib_send_wr *wr,
>  
>  	if (qp->is_user) {
>  		/* Utilize process context to do protocol processing */
> -		rxe_run_task(&qp->req.task, 0);
> +		rxe_run_work(&qp->req.work, 0);
>  		return 0;
>  	} else
>  		return rxe_post_send_kernel(qp, wr, bad_wr);
> @@ -761,7 +761,7 @@ static int rxe_post_recv(struct ib_qp *ibqp, const struct ib_recv_wr *wr,
>  	spin_unlock_irqrestore(&rq->producer_lock, flags);
>  
>  	if (qp->resp.state == QP_STATE_ERROR)
> -		rxe_run_task(&qp->resp.task, 1);
> +		rxe_run_work(&qp->resp.work, 1);
>  
>  err1:
>  	return err;
> diff --git a/drivers/infiniband/sw/rxe/rxe_verbs.h b/drivers/infiniband/sw/rxe/rxe_verbs.h
> index a51819d0c345..b09b4cb9897a 100644
> --- a/drivers/infiniband/sw/rxe/rxe_verbs.h
> +++ b/drivers/infiniband/sw/rxe/rxe_verbs.h
> @@ -10,7 +10,7 @@
>  #include <linux/interrupt.h>
>  #include <linux/workqueue.h>
>  #include "rxe_pool.h"
> -#include "rxe_task.h"
> +#include "rxe_wq.h"
>  #include "rxe_hw_counters.h"
>  
>  static inline int pkey_match(u16 key1, u16 key2)
> @@ -125,7 +125,7 @@ struct rxe_req_info {
>  	int			need_retry;
>  	int			wait_for_rnr_timer;
>  	int			noack_pkts;
> -	struct rxe_task		task;
> +	struct rxe_work		work;
>  };
>  
>  struct rxe_comp_info {
> @@ -137,7 +137,7 @@ struct rxe_comp_info {
>  	int			started_retry;
>  	u32			retry_cnt;
>  	u32			rnr_retry;
> -	struct rxe_task		task;
> +	struct rxe_work		work;
>  };
>  
>  enum rdatm_res_state {
> @@ -204,7 +204,7 @@ struct rxe_resp_info {
>  	unsigned int		res_head;
>  	unsigned int		res_tail;
>  	struct resp_res		*res;
> -	struct rxe_task		task;
> +	struct rxe_work		work;
>  };
>  
>  struct rxe_qp {
> diff --git a/drivers/infiniband/sw/rxe/rxe_wq.c b/drivers/infiniband/sw/rxe/rxe_wq.c
> new file mode 100644
> index 000000000000..8b35186eac85
> --- /dev/null
> +++ b/drivers/infiniband/sw/rxe/rxe_wq.c
> @@ -0,0 +1,161 @@
> +// SPDX-License-Identifier: GPL-2.0 OR Linux-OpenIB
> +/*
> + * Copyright (c) 2016 Mellanox Technologies Ltd. All rights reserved.
> + * Copyright (c) 2015 System Fabric Works, Inc. All rights reserved.
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/interrupt.h>
> +#include <linux/hardirq.h>
> +
> +#include "rxe.h"
> +
> +int __rxe_do_work(struct rxe_work *work)
> +
> +{
> +	int ret;
> +
> +	while ((ret = work->func(work->arg)) == 0)
> +		;
> +
> +	work->ret = ret;
> +
> +	return ret;
> +}
> +
> +/*
> + * this locking is due to a potential race where
> + * a second caller finds the work already running
> + * but looks just after the last call to func
> + */
> +void rxe_do_work(struct work_struct *w)
> +{
> +	int cont;
> +	int ret;
> +
> +	struct rxe_work *work = container_of(w, typeof(*work), work);
> +	unsigned int iterations = RXE_MAX_ITERATIONS;
> +
> +	spin_lock_bh(&work->state_lock);
> +	switch (work->state) {
> +	case WQ_STATE_START:
> +		work->state = WQ_STATE_BUSY;
> +		spin_unlock_bh(&work->state_lock);
> +		break;
> +
> +	case WQ_STATE_BUSY:
> +		work->state = WQ_STATE_ARMED;
> +		fallthrough;
> +	case WQ_STATE_ARMED:
> +		spin_unlock_bh(&work->state_lock);
> +		return;
> +
> +	default:
> +		spin_unlock_bh(&work->state_lock);
> +		pr_warn("%s failed with bad state %d\n", __func__, work->state);
> +		return;
> +	}
> +
> +	do {
> +		cont = 0;
> +		ret = work->func(work->arg);
> +
> +		spin_lock_bh(&work->state_lock);
> +		switch (work->state) {
> +		case WQ_STATE_BUSY:
> +			if (ret) {
> +				work->state = WQ_STATE_START;
> +			} else if (iterations--) {
> +				cont = 1;
> +			} else {
> +				/* reschedule the work and exit
> +				 * the loop to give up the cpu
> +				 */
> +				queue_work(work->worker, &work->work);
> +				work->state = WQ_STATE_START;
> +			}
> +			break;
> +
> +		/* someone tried to run the work since the last time we called
> +		 * func, so we will call one more time regardless of the
> +		 * return value
> +		 */
> +		case WQ_STATE_ARMED:
> +			work->state = WQ_STATE_BUSY;
> +			cont = 1;
> +			break;
> +
> +		default:
> +			pr_warn("%s failed with bad state %d\n", __func__,
> +				work->state);
> +		}
> +		spin_unlock_bh(&work->state_lock);
> +	} while (cont);
> +
> +	work->ret = ret;
> +}
> +
> +int rxe_init_work(void *obj, struct rxe_work *work,
> +		  void *arg, int (*func)(void *), char *name)
> +{
> +	work->obj	= obj;
> +	work->arg	= arg;
> +	work->func	= func;
> +	snprintf(work->name, sizeof(work->name), "%s", name);
> +	work->destroyed	= false;
> +	atomic_set(&work->suspended, 0);
> +
> +	work->worker = create_singlethread_workqueue(name);
> +	INIT_WORK(&work->work, rxe_do_work);
> +
> +	work->state = WQ_STATE_START;
> +	spin_lock_init(&work->state_lock);
> +
> +	return 0;
> +}
> +
> +void rxe_cleanup_work(struct rxe_work *work)
> +{
> +	bool idle;
> +
> +	/*
> +	 * Mark the work, then wait for it to finish. It might be
> +	 * running in a non-workqueue (direct call) context.
> +	 */
> +	work->destroyed = true;
> +	flush_workqueue(work->worker);
> +
> +	do {
> +		spin_lock_bh(&work->state_lock);
> +		idle = (work->state == WQ_STATE_START);
> +		spin_unlock_bh(&work->state_lock);
> +	} while (!idle);
> +
> +	destroy_workqueue(work->worker);
> +}
> +
> +void rxe_run_work(struct rxe_work *work, int sched)
> +{
> +	if (work->destroyed)
> +		return;
> +
> +	/* busy-loop while qp reset is in progress */
> +	while (atomic_read(&work->suspended))
> +		continue;
> +
> +	if (sched)
> +		queue_work(work->worker, &work->work);
> +	else
> +		rxe_do_work(&work->work);
> +}
> +
> +void rxe_disable_work(struct rxe_work *work)
> +{
> +	atomic_inc(&work->suspended);
> +	flush_workqueue(work->worker);
> +}
> +
> +void rxe_enable_work(struct rxe_work *work)
> +{
> +	atomic_dec(&work->suspended);
> +}
> diff --git a/drivers/infiniband/sw/rxe/rxe_wq.h b/drivers/infiniband/sw/rxe/rxe_wq.h
> new file mode 100644
> index 000000000000..b40af598dcc0
> --- /dev/null
> +++ b/drivers/infiniband/sw/rxe/rxe_wq.h
> @@ -0,0 +1,71 @@
> +/* SPDX-License-Identifier: GPL-2.0 OR Linux-OpenIB */
> +/*
> + * Copyright (c) 2016 Mellanox Technologies Ltd. All rights reserved.
> + * Copyright (c) 2015 System Fabric Works, Inc. All rights reserved.
> + */
> +
> +#ifndef RXE_WQ_H
> +#define RXE_WQ_H
> +
> +enum {
> +	WQ_STATE_START	= 0,
> +	WQ_STATE_BUSY		= 1,
> +	WQ_STATE_ARMED	= 2,
> +};
> +
> +/*
> + * data structure to describe a 'work' which is a short
> + * function that returns 0 as long as it needs to be
> + * called again.
> + */
> +struct rxe_work {
> +	void			*obj;
> +	struct workqueue_struct	*worker;
> +	struct work_struct	work;
> +	int			state;
> +	spinlock_t		state_lock; /* spinlock for work state */
> +	void			*arg;
> +	int			(*func)(void *arg);
> +	int			ret;
> +	char			name[16];
> +	bool			destroyed;
> +	atomic_t		suspended; /* used to {dis,en}able workqueue */
> +};
> +
> +/*
> + * init rxe_work structure
> + *	arg  => parameter to pass to fcn
> + *	func => function to call until it returns != 0
> + */
> +int rxe_init_work(void *obj, struct rxe_work *work,
> +		  void *arg, int (*func)(void *), char *name);
> +
> +/* cleanup work */
> +void rxe_cleanup_work(struct rxe_work *work);
> +
> +/*
> + * raw call to func in loop without any checking
> + * can call when workqueues are suspended.
> + */
> +int __rxe_do_work(struct rxe_work *work);
> +
> +/*
> + * common function called by any of the main workqueues
> + * If there is any chance that there is additional
> + * work to do someone must reschedule the work before
> + * leaving
> + */
> +void rxe_do_work(struct work_struct *w);
> +
> +/* run a work, else schedule it to run as a workqueue, The decision
> + * to run or schedule workqueue is based on the parameter sched.
> + */
> +void rxe_run_work(struct rxe_work *work, int sched);
> +
> +/* keep a work from scheduling */
> +void rxe_disable_work(struct rxe_work *work);
> +
> +/* allow work to run */
> +void rxe_enable_work(struct rxe_work *work);
> +
> +#endif /* RXE_WQ_H */

Daiskuke,

We (hpe) have an internal patch set that also allows using work queues instead of tasklets.
There is a certain amount of work to allow control over cpu assignment from ulp or application
level. This is critical for high performance in multithreaded IO applications. It would be in
both of our interests if we could find a common implementation that works for everyone.

Perhaps we could arrange for a call to discuss?

Bob Pearson