RDMA/rxe: Add workqueue support for rxe tasks

Replace tasklets by work queues for the three main rxe tasklets:
rxe_requester, rxe_completer and rxe_responder.

work queues are a more modern way to process work from an IRQ and provide
more control over how that work is run for future patches.

Link: https://lore.kernel.org/r/20230428171321.5774-1-rpearsonhpe@gmail.com
Signed-off-by: Ian Ziemba <ian.ziemba@hpe.com>
Signed-off-by: Bob Pearson <rpearsonhpe@gmail.com>
Reviewed-by: Daisuke Matsuda <matsuda-daisuke@fujitsu.com>
Tested-by: Daisuke Matsuda <matsuda-daisuke@fujitsu.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

Author: Bob Pearson

drivers/infiniband/sw/rxe/rxe.c

@@ -212,10 +212,16 @@ static int __init rxe_module_init(void)
 {
 	int err;
 
-	err = rxe_net_init();
+	err = rxe_alloc_wq();
 	if (err)
 		return err;
 
+	err = rxe_net_init();
+	if (err) {
+		rxe_destroy_wq();
+		return err;
+	}
+
 	rdma_link_register(&rxe_link_ops);
 	pr_info("loaded\n");
 	return 0;
@@ -226,6 +232,7 @@ static void __exit rxe_module_exit(void)
 	rdma_link_unregister(&rxe_link_ops);
 	ib_unregister_driver(RDMA_DRIVER_RXE);
 	rxe_net_exit();
+	rxe_destroy_wq();
 
 	pr_info("unloaded\n");
 }

drivers/infiniband/sw/rxe/rxe_task.c

@@ -6,8 +6,24 @@
 
 #include "rxe.h"
 
+static struct workqueue_struct *rxe_wq;
+
+int rxe_alloc_wq(void)
+{
+	rxe_wq = alloc_workqueue("rxe_wq", WQ_UNBOUND, WQ_MAX_ACTIVE);
+	if (!rxe_wq)
+		return -ENOMEM;
+
+	return 0;
+}
+
+void rxe_destroy_wq(void)
+{
+	destroy_workqueue(rxe_wq);
+}
+
 /* Check if task is idle i.e. not running, not scheduled in
- * tasklet queue and not draining. If so move to busy to
+ * work queue and not draining. If so move to busy to
  * reserve a slot in do_task() by setting to busy and taking
  * a qp reference to cover the gap from now until the task finishes.
  * state will move out of busy if task returns a non zero value
@@ -21,9 +37,6 @@ static bool __reserve_if_idle(struct rxe_task *task)
 {
 	WARN_ON(rxe_read(task->qp) <= 0);
 
-	if (task->tasklet.state & BIT(TASKLET_STATE_SCHED))
-		return false;
-
 	if (task->state == TASK_STATE_IDLE) {
 		rxe_get(task->qp);
 		task->state = TASK_STATE_BUSY;
@@ -38,15 +51,15 @@ static bool __reserve_if_idle(struct rxe_task *task)
 }
 
 /* check if task is idle or drained and not currently
- * scheduled in the tasklet queue. This routine is
+ * scheduled in the work queue. This routine is
  * called by rxe_cleanup_task or rxe_disable_task to
  * see if the queue is empty.
  * Context: caller should hold task->lock.
  * Returns true if done else false.
  */
 static bool __is_done(struct rxe_task *task)
 {
-	if (task->tasklet.state & BIT(TASKLET_STATE_SCHED))
+	if (work_pending(&task->work))
 		return false;
 
 	if (task->state == TASK_STATE_IDLE ||
@@ -77,23 +90,23 @@ static bool is_done(struct rxe_task *task)
  * schedules the task. They must call __reserve_if_idle to
  * move the task to busy before calling or scheduling.
  * The task can also be moved to drained or invalid
- * by calls to rxe-cleanup_task or rxe_disable_task.
+ * by calls to rxe_cleanup_task or rxe_disable_task.
  * In that case tasks which get here are not executed but
  * just flushed. The tasks are designed to look to see if
- * there is work to do and do part of it before returning
+ * there is work to do and then do part of it before returning
  * here with a return value of zero until all the work
- * has been consumed then it retuens a non-zero value.
+ * has been consumed then it returns a non-zero value.
  * The number of times the task can be run is limited by
  * max iterations so one task cannot hold the cpu forever.
+ * If the limit is hit and work remains the task is rescheduled.
  */
-static void do_task(struct tasklet_struct *t)
+static void do_task(struct rxe_task *task)
 {
-	int cont;
-	int ret;
-	struct rxe_task *task = from_tasklet(task, t, tasklet);
 	unsigned int iterations;
 	unsigned long flags;
 	int resched = 0;
+	int cont;
+	int ret;
 
 	WARN_ON(rxe_read(task->qp) <= 0);
 
@@ -115,48 +128,47 @@ static void do_task(struct tasklet_struct *t)
 		} while (ret == 0 && iterations-- > 0);
 
 		spin_lock_irqsave(&task->lock, flags);
+		/* we're not done yet but we ran out of iterations.
+		 * yield the cpu and reschedule the task
+		 */
+		if (!ret) {
+			task->state = TASK_STATE_IDLE;
+			resched = 1;
+			goto exit;
+		}
+
 		switch (task->state) {
 		case TASK_STATE_BUSY:
-			if (ret) {
-				task->state = TASK_STATE_IDLE;
-			} else {
-				/* This can happen if the client
-				 * can add work faster than the
-				 * tasklet can finish it.
-				 * Reschedule the tasklet and exit
-				 * the loop to give up the cpu
-				 */
-				task->state = TASK_STATE_IDLE;
-				resched = 1;
-			}
+			task->state = TASK_STATE_IDLE;
 			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
+		/* someone tried to schedule the task while we
+		 * were running, keep going
 		 */
 		case TASK_STATE_ARMED:
 			task->state = TASK_STATE_BUSY;
 			cont = 1;
 			break;
 
 		case TASK_STATE_DRAINING:
-			if (ret)
-				task->state = TASK_STATE_DRAINED;
-			else
-				cont = 1;
+			task->state = TASK_STATE_DRAINED;
 			break;
 
 		default:
 			WARN_ON(1);
-			rxe_info_qp(task->qp, "unexpected task state = %d", task->state);
+			rxe_dbg_qp(task->qp, "unexpected task state = %d",
+				   task->state);
+			task->state = TASK_STATE_IDLE;
 		}
 
+exit:
 		if (!cont) {
 			task->num_done++;
 			if (WARN_ON(task->num_done != task->num_sched))
-				rxe_err_qp(task->qp, "%ld tasks scheduled, %ld tasks done",
-					   task->num_sched, task->num_done);
+				rxe_dbg_qp(
+					task->qp,
+					"%ld tasks scheduled, %ld tasks done",
+					task->num_sched, task->num_done);
 		}
 		spin_unlock_irqrestore(&task->lock, flags);
 	} while (cont);
@@ -169,18 +181,22 @@ static void do_task(struct tasklet_struct *t)
 	rxe_put(task->qp);
 }
 
+/* wrapper around do_task to fix argument for work queue */
+static void do_work(struct work_struct *work)
+{
+	do_task(container_of(work, struct rxe_task, work));
+}
+
 int rxe_init_task(struct rxe_task *task, struct rxe_qp *qp,
 		  int (*func)(struct rxe_qp *))
 {
 	WARN_ON(rxe_read(qp) <= 0);
 
 	task->qp = qp;
 	task->func = func;
-
-	tasklet_setup(&task->tasklet, do_task);
-
 	task->state = TASK_STATE_IDLE;
 	spin_lock_init(&task->lock);
+	INIT_WORK(&task->work, do_work);
 
 	return 0;
 }
@@ -213,8 +229,6 @@ void rxe_cleanup_task(struct rxe_task *task)
 	while (!is_done(task))
 		cond_resched();
 
-	tasklet_kill(&task->tasklet);
-
 	spin_lock_irqsave(&task->lock, flags);
 	task->state = TASK_STATE_INVALID;
 	spin_unlock_irqrestore(&task->lock, flags);
@@ -226,7 +240,7 @@ void rxe_cleanup_task(struct rxe_task *task)
 void rxe_run_task(struct rxe_task *task)
 {
 	unsigned long flags;
-	int run;
+	bool run;
 
 	WARN_ON(rxe_read(task->qp) <= 0);
 
@@ -235,11 +249,11 @@ void rxe_run_task(struct rxe_task *task)
 	spin_unlock_irqrestore(&task->lock, flags);
 
 	if (run)
-		do_task(&task->tasklet);
+		do_task(task);
 }
 
-/* schedule the task to run later as a tasklet.
- * the tasklet)schedule call can be called holding
+/* schedule the task to run later as a work queue entry.
+ * the queue_work call can be called holding
  * the lock.
  */
 void rxe_sched_task(struct rxe_task *task)
@@ -250,7 +264,7 @@ void rxe_sched_task(struct rxe_task *task)
 
 	spin_lock_irqsave(&task->lock, flags);
 	if (__reserve_if_idle(task))
-		tasklet_schedule(&task->tasklet);
+		queue_work(rxe_wq, &task->work);
 	spin_unlock_irqrestore(&task->lock, flags);
 }
 
@@ -277,7 +291,9 @@ void rxe_disable_task(struct rxe_task *task)
 	while (!is_done(task))
 		cond_resched();
 
-	tasklet_disable(&task->tasklet);
+	spin_lock_irqsave(&task->lock, flags);
+	task->state = TASK_STATE_DRAINED;
+	spin_unlock_irqrestore(&task->lock, flags);
 }
 
 void rxe_enable_task(struct rxe_task *task)
@@ -291,7 +307,7 @@ void rxe_enable_task(struct rxe_task *task)
 		spin_unlock_irqrestore(&task->lock, flags);
 		return;
 	}
+
 	task->state = TASK_STATE_IDLE;
-	tasklet_enable(&task->tasklet);
 	spin_unlock_irqrestore(&task->lock, flags);
 }

drivers/infiniband/sw/rxe/rxe_task.h

@@ -22,7 +22,7 @@ enum {
  * called again.
  */
 struct rxe_task {
-	struct tasklet_struct	tasklet;
+	struct work_struct	work;
 	int			state;
 	spinlock_t		lock;
 	struct rxe_qp		*qp;
@@ -32,6 +32,10 @@ struct rxe_task {
 	long			num_done;
 };
 
+int rxe_alloc_wq(void);
+
+void rxe_destroy_wq(void);
+
 /*
  * init rxe_task structure
  *	qp  => parameter to pass to func