linux-kernel - Re: [PATCH for-next v5 1/7] RDMA/rxe: Always defer tasks on responder and completer to workqueue

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Message-ID: <660e05c8-9016-f97a-1af3-341eec8e911e@gmail.com>
Date:   Thu, 18 May 2023 17:25:39 -0500
From:   Bob Pearson <rpearsonhpe@...il.com>
To:     Daisuke Matsuda <matsuda-daisuke@...itsu.com>,
        linux-rdma@...r.kernel.org, leonro@...dia.com, jgg@...dia.com,
        zyjzyj2000@...il.com
Cc:     linux-kernel@...r.kernel.org, yangx.jy@...itsu.com,
        lizhijian@...itsu.com, y-goto@...itsu.com
Subject: Re: [PATCH for-next v5 1/7] RDMA/rxe: Always defer tasks on responder
 and completer to workqueue

On 5/18/23 03:21, Daisuke Matsuda wrote:
> Both responder and completer need to sleep to execute page-fault when used
> with ODP. It can happen when they are going to access user MRs, so tasks
> must be executed in process context for such cases.
> 
> Additionally, current implementation seldom defers tasks to workqueue, but
> instead defers to a softirq context running do_task(). It is called from
> rxe_resp_queue_pkt() and rxe_comp_queue_pkt() in SOFTIRQ_NET_RX context and
> can last until maximum RXE_MAX_ITERATIONS (=1024) loops are executed. The
> problem is the that task execuion appears to be anonymous loads in the
> system and that the loop can throttle other softirqs on the same CPU.
> 
> This patch makes responder and completer codes run in process context for
> ODP and the problem described above.
> 
> Signed-off-by: Daisuke Matsuda <matsuda-daisuke@...itsu.com>
> ---
>  drivers/infiniband/sw/rxe/rxe_comp.c        | 12 +-----------
>  drivers/infiniband/sw/rxe/rxe_hw_counters.c |  1 -
>  drivers/infiniband/sw/rxe/rxe_hw_counters.h |  1 -
>  drivers/infiniband/sw/rxe/rxe_resp.c        | 13 +------------
>  4 files changed, 2 insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/infiniband/sw/rxe/rxe_comp.c b/drivers/infiniband/sw/rxe/rxe_comp.c
> index db18ace74d2b..671fdb645030 100644
> --- a/drivers/infiniband/sw/rxe/rxe_comp.c
> +++ b/drivers/infiniband/sw/rxe/rxe_comp.c
> @@ -128,18 +128,8 @@ void retransmit_timer(struct timer_list *t)
>  
>  void rxe_comp_queue_pkt(struct rxe_qp *qp, struct sk_buff *skb)
>  {
> -	int must_sched;
> -
>  	skb_queue_tail(&qp->resp_pkts, skb);
> -
> -	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);
> -
> -	if (must_sched)
> -		rxe_sched_task(&qp->comp.task);
> -	else
> -		rxe_run_task(&qp->comp.task);
> +	rxe_sched_task(&qp->comp.task);
>  }
>  
>  static inline enum comp_state get_wqe(struct rxe_qp *qp,
> diff --git a/drivers/infiniband/sw/rxe/rxe_hw_counters.c b/drivers/infiniband/sw/rxe/rxe_hw_counters.c
> index a012522b577a..dc23cf3a6967 100644
> --- a/drivers/infiniband/sw/rxe/rxe_hw_counters.c
> +++ b/drivers/infiniband/sw/rxe/rxe_hw_counters.c
> @@ -14,7 +14,6 @@ static const struct rdma_stat_desc rxe_counter_descs[] = {
>  	[RXE_CNT_RCV_RNR].name             =  "rcvd_rnr_err",
>  	[RXE_CNT_SND_RNR].name             =  "send_rnr_err",
>  	[RXE_CNT_RCV_SEQ_ERR].name         =  "rcvd_seq_err",
> -	[RXE_CNT_COMPLETER_SCHED].name     =  "ack_deferred",
>  	[RXE_CNT_RETRY_EXCEEDED].name      =  "retry_exceeded_err",
>  	[RXE_CNT_RNR_RETRY_EXCEEDED].name  =  "retry_rnr_exceeded_err",
>  	[RXE_CNT_COMP_RETRY].name          =  "completer_retry_err",
> diff --git a/drivers/infiniband/sw/rxe/rxe_hw_counters.h b/drivers/infiniband/sw/rxe/rxe_hw_counters.h
> index 71f4d4fa9dc8..303da0e3134a 100644
> --- a/drivers/infiniband/sw/rxe/rxe_hw_counters.h
> +++ b/drivers/infiniband/sw/rxe/rxe_hw_counters.h
> @@ -18,7 +18,6 @@ enum rxe_counters {
>  	RXE_CNT_RCV_RNR,
>  	RXE_CNT_SND_RNR,
>  	RXE_CNT_RCV_SEQ_ERR,
> -	RXE_CNT_COMPLETER_SCHED,
>  	RXE_CNT_RETRY_EXCEEDED,
>  	RXE_CNT_RNR_RETRY_EXCEEDED,
>  	RXE_CNT_COMP_RETRY,
> diff --git a/drivers/infiniband/sw/rxe/rxe_resp.c b/drivers/infiniband/sw/rxe/rxe_resp.c
> index 68f6cd188d8e..ba0222bfce9e 100644
> --- a/drivers/infiniband/sw/rxe/rxe_resp.c
> +++ b/drivers/infiniband/sw/rxe/rxe_resp.c
> @@ -46,21 +46,10 @@ static char *resp_state_name[] = {
>  	[RESPST_EXIT]				= "EXIT",
>  };
>  
> -/* 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);
> -
>  	skb_queue_tail(&qp->req_pkts, skb);
> -
> -	must_sched = (pkt->opcode == IB_OPCODE_RC_RDMA_READ_REQUEST) ||
> -			(skb_queue_len(&qp->req_pkts) > 1);
> -
> -	if (must_sched)
> -		rxe_sched_task(&qp->resp.task);
> -	else
> -		rxe_run_task(&qp->resp.task);
> +	rxe_sched_task(&qp->resp.task);
>  }
>  
>  static inline enum resp_states get_req(struct rxe_qp *qp,

Looks good.

Reviewed-by: Bob Pearson <rpearsonhpe@...il.com>