s390/zcrypt: get rid of ap_poll_requests

The poll thread of the AP bus is burning CPU while waiting for
crypto requests to complete. We can as well burn a few more cycles
in the poll thread to check if there are pending requests and
remove the atomic operations with the ap_poll_requests.
This improves the code if the machine has adapter interrupts.
Signed-off-by: Harald Freudenberger <freude@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/crypto/ap_bus.c

@@ -91,7 +91,6 @@ static DECLARE_WORK(ap_scan_work, ap_scan_bus);
  */
 static void ap_tasklet_fn(unsigned long);
 static DECLARE_TASKLET(ap_tasklet, ap_tasklet_fn, 0);
-static atomic_t ap_poll_requests = ATOMIC_INIT(0);
 static DECLARE_WAIT_QUEUE_HEAD(ap_poll_wait);
 static struct task_struct *ap_poll_kthread = NULL;
 static DEFINE_MUTEX(ap_poll_thread_mutex);
@@ -419,7 +418,6 @@ static struct ap_queue_status ap_sm_recv(struct ap_device *ap_dev)
 			 ap_dev->reply->message, ap_dev->reply->length);
 	switch (status.response_code) {
 	case AP_RESPONSE_NORMAL:
-		atomic_dec(&ap_poll_requests);
 		ap_dev->queue_count--;
 		if (ap_dev->queue_count > 0)
 			mod_timer(&ap_dev->timeout,
@@ -436,7 +434,6 @@ static struct ap_queue_status ap_sm_recv(struct ap_device *ap_dev)
 		if (!status.queue_empty || ap_dev->queue_count <= 0)
 			break;
 		/* The card shouldn't forget requests but who knows. */
-		atomic_sub(ap_dev->queue_count, &ap_poll_requests);
 		ap_dev->queue_count = 0;
 		list_splice_init(&ap_dev->pendingq, &ap_dev->requestq);
 		ap_dev->requestq_count += ap_dev->pendingq_count;
@@ -524,7 +521,6 @@ static enum ap_wait ap_sm_write(struct ap_device *ap_dev)
 			   ap_msg->message, ap_msg->length, ap_msg->special);
 	switch (status.response_code) {
 	case AP_RESPONSE_NORMAL:
-		atomic_inc(&ap_poll_requests);
 		ap_dev->queue_count++;
 		if (ap_dev->queue_count == 1)
 			mod_timer(&ap_dev->timeout,
@@ -796,6 +792,27 @@ static void ap_tasklet_fn(unsigned long dummy)
 	ap_sm_wait(wait);
 }
 
+static int ap_pending_requests(void)
+{
+	struct ap_device *ap_dev;
+	int id, pending = 0;
+
+	for (id = 0; pending == 0 && id < AP_DEVICES; id++) {
+		spin_lock_bh(&ap_device_list_lock);
+		list_for_each_entry(ap_dev, &ap_device_list, list) {
+			spin_lock_bh(&ap_dev->lock);
+			if (ap_dev->queue_count)
+				pending = 1;
+			spin_unlock_bh(&ap_dev->lock);
+			if (pending)
+				break;
+		}
+		spin_unlock_bh(&ap_device_list_lock);
+	}
+
+	return pending;
+}
+
 /**
  * ap_poll_thread(): Thread that polls for finished requests.
  * @data: Unused pointer
@@ -815,8 +832,7 @@ static int ap_poll_thread(void *data)
 	while (!kthread_should_stop()) {
 		add_wait_queue(&ap_poll_wait, &wait);
 		set_current_state(TASK_INTERRUPTIBLE);
-		if (ap_suspend_flag ||
-		    atomic_read(&ap_poll_requests) <= 0) {
+		if (ap_suspend_flag || !ap_pending_requests()) {
 			schedule();
 			try_to_freeze();
 		}
@@ -828,7 +844,8 @@ static int ap_poll_thread(void *data)
 			continue;
 		}
 		ap_tasklet_fn(0);
-	} while (!kthread_should_stop());
+	}
+
 	return 0;
 }
 
@@ -1267,9 +1284,6 @@ static int ap_device_remove(struct device *dev)
 	spin_unlock_bh(&ap_device_list_lock);
 	if (ap_drv->remove)
 		ap_drv->remove(ap_dev);
-	spin_lock_bh(&ap_dev->lock);
-	atomic_sub(ap_dev->queue_count, &ap_poll_requests);
-	spin_unlock_bh(&ap_dev->lock);
 	return 0;
 }