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

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Date:   Thu, 18 May 2023 17:21:46 +0900
From:   Daisuke Matsuda <matsuda-daisuke@...itsu.com>
To:     linux-rdma@...r.kernel.org, leonro@...dia.com, jgg@...dia.com,
        zyjzyj2000@...il.com
Cc:     linux-kernel@...r.kernel.org, rpearsonhpe@...il.com,
        yangx.jy@...itsu.com, lizhijian@...itsu.com, y-goto@...itsu.com,
        Daisuke Matsuda <matsuda-daisuke@...itsu.com>
Subject: [PATCH for-next v5 1/7] RDMA/rxe: Always defer tasks on responder and completer to workqueue

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,
-- 
2.39.1