scsi: zfcp: Lift Request Queue tasklet & timer from qdio

The qdio layer currently provides its own infrastructure to scan for
Request Queue completions & to report them to the device driver.  This
comes with several drawbacks - having an async tasklet & timer construct in
qdio introduces additional lifetime complexity, and makes it harder to
integrate them with the rest of the device driver. The timeouts are also
currently hard-coded, and can't be tweaked without affecting other qdio
drivers (ie. qeth).

But due to recent enhancements to the qdio layer, zfcp can actually take
full control of the Request Queue completion processing. It merely needs to
opt-out from the qdio layer mechanisms by setting the scan_threshold to 0,
and then use qdio_inspect_queue() to scan for completions.

So re-implement the tasklet & timer mechanism in zfcp, while initially
copying the scan conditions from qdio's handle_outbound() and
qdio_outbound_tasklet(). One minor behavioural change is that
zfcp_qdio_send() will unconditionally reduce the timeout to 1 HZ, rather
than leaving it at 10 Hz if it was last armed by the tasklet. This just
makes things more consistent. Also note that we can drop a lot of the
accumulated cruft in qdio_outbound_tasklet(), as zfcp doesn't even use PCI
interrupt requests any longer.

This also slightly touches the Response Queue processing, as
qdio_get_next_buffers() will no longer implicitly scan for Request Queue
completions. So complete the migration to qdio_inspect_queue() here as well
and make the tasklet_schedule() visible.

Link: https://lore.kernel.org/r/018d3ddd029f8d6ac00cf4184880288c637c4fd1.1618417667.git.bblock@linux.ibm.com
Reviewed-by: Benjamin Block <bblock@linux.ibm.com>
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: Benjamin Block <bblock@linux.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/s390/scsi/zfcp_qdio.c

@@ -20,6 +20,9 @@ static bool enable_multibuffer = true;
 module_param_named(datarouter, enable_multibuffer, bool, 0400);
 MODULE_PARM_DESC(datarouter, "Enable hardware data router support (default on)");
 
+#define ZFCP_QDIO_REQUEST_RESCAN_MSECS	(MSEC_PER_SEC * 10)
+#define ZFCP_QDIO_REQUEST_SCAN_MSECS	MSEC_PER_SEC
+
 static void zfcp_qdio_handler_error(struct zfcp_qdio *qdio, char *dbftag,
 				    unsigned int qdio_err)
 {
@@ -70,15 +73,41 @@ static void zfcp_qdio_int_req(struct ccw_device *cdev, unsigned int qdio_err,
 		zfcp_qdio_handler_error(qdio, "qdireq1", qdio_err);
 		return;
 	}
+}
 
+static void zfcp_qdio_request_tasklet(struct tasklet_struct *tasklet)
+{
+	struct zfcp_qdio *qdio = from_tasklet(qdio, tasklet, request_tasklet);
+	struct ccw_device *cdev = qdio->adapter->ccw_device;
+	unsigned int start, error;
+	int completed;
+
+	completed = qdio_inspect_queue(cdev, 0, false, &start, &error);
+	if (completed > 0) {
+		if (error) {
+			zfcp_qdio_handler_error(qdio, "qdreqt1", error);
+		} else {
 			/* cleanup all SBALs being program-owned now */
-	zfcp_qdio_zero_sbals(qdio->req_q, idx, count);
+			zfcp_qdio_zero_sbals(qdio->req_q, start, completed);
 
 			spin_lock_irq(&qdio->stat_lock);
 			zfcp_qdio_account(qdio);
 			spin_unlock_irq(&qdio->stat_lock);
-	atomic_add(count, &qdio->req_q_free);
+			atomic_add(completed, &qdio->req_q_free);
 			wake_up(&qdio->req_q_wq);
+		}
+	}
+
+	if (atomic_read(&qdio->req_q_free) < QDIO_MAX_BUFFERS_PER_Q)
+		timer_reduce(&qdio->request_timer,
+			     jiffies + msecs_to_jiffies(ZFCP_QDIO_REQUEST_RESCAN_MSECS));
+}
+
+static void zfcp_qdio_request_timer(struct timer_list *timer)
+{
+	struct zfcp_qdio *qdio = from_timer(qdio, timer, request_timer);
+
+	tasklet_schedule(&qdio->request_tasklet);
 }
 
 static void zfcp_qdio_int_resp(struct ccw_device *cdev, unsigned int qdio_err,
@@ -139,8 +168,11 @@ static void zfcp_qdio_irq_tasklet(struct tasklet_struct *tasklet)
 	unsigned int start, error;
 	int completed;
 
-	/* Check the Response Queue, and kick off the Request Queue tasklet: */
+	if (atomic_read(&qdio->req_q_free) < QDIO_MAX_BUFFERS_PER_Q)
-	completed = qdio_get_next_buffers(cdev, 0, &start, &error);
+		tasklet_schedule(&qdio->request_tasklet);
+
+	/* Check the Response Queue: */
+	completed = qdio_inspect_queue(cdev, 0, true, &start, &error);
 	if (completed < 0)
 		return;
 	if (completed > 0)
@@ -286,7 +318,7 @@ int zfcp_qdio_send(struct zfcp_qdio *qdio, struct zfcp_qdio_req *q_req)
 
 	/*
 	 * This should actually be a spin_lock_bh(stat_lock), to protect against
-	 * zfcp_qdio_int_req() in tasklet context.
+	 * Request Queue completion processing in tasklet context.
 	 * But we can't do so (and are safe), as we always get called with IRQs
 	 * disabled by spin_lock_irq[save](req_q_lock).
 	 */
@@ -308,6 +340,12 @@ int zfcp_qdio_send(struct zfcp_qdio *qdio, struct zfcp_qdio_req *q_req)
 		return retval;
 	}
 
+	if (atomic_read(&qdio->req_q_free) <= 2 * ZFCP_QDIO_MAX_SBALS_PER_REQ)
+		tasklet_schedule(&qdio->request_tasklet);
+	else
+		timer_reduce(&qdio->request_timer,
+			     jiffies + msecs_to_jiffies(ZFCP_QDIO_REQUEST_SCAN_MSECS));
+
 	/* account for transferred buffers */
 	qdio->req_q_idx += sbal_number;
 	qdio->req_q_idx %= QDIO_MAX_BUFFERS_PER_Q;
@@ -368,6 +406,8 @@ void zfcp_qdio_close(struct zfcp_qdio *qdio)
 	wake_up(&qdio->req_q_wq);
 
 	tasklet_disable(&qdio->irq_tasklet);
+	tasklet_disable(&qdio->request_tasklet);
+	del_timer_sync(&qdio->request_timer);
 	qdio_stop_irq(adapter->ccw_device);
 	qdio_shutdown(adapter->ccw_device, QDIO_FLAG_CLEANUP_USING_CLEAR);
 
@@ -428,8 +468,6 @@ int zfcp_qdio_open(struct zfcp_qdio *qdio)
 	init_data.int_parm = (unsigned long) qdio;
 	init_data.input_sbal_addr_array = input_sbals;
 	init_data.output_sbal_addr_array = output_sbals;
-	init_data.scan_threshold =
-		QDIO_MAX_BUFFERS_PER_Q - ZFCP_QDIO_MAX_SBALS_PER_REQ * 2;
 
 	if (qdio_establish(cdev, &init_data))
 		goto failed_establish;
@@ -471,6 +509,8 @@ int zfcp_qdio_open(struct zfcp_qdio *qdio)
 	atomic_set(&qdio->req_q_free, QDIO_MAX_BUFFERS_PER_Q);
 	atomic_or(ZFCP_STATUS_ADAPTER_QDIOUP, &qdio->adapter->status);
 
+	/* Enable processing for Request Queue completions: */
+	tasklet_enable(&qdio->request_tasklet);
 	/* Enable processing for QDIO interrupts: */
 	tasklet_enable(&qdio->irq_tasklet);
 	/* This results in a qdio_start_irq(): */
@@ -494,6 +534,7 @@ void zfcp_qdio_destroy(struct zfcp_qdio *qdio)
 		return;
 
 	tasklet_kill(&qdio->irq_tasklet);
+	tasklet_kill(&qdio->request_tasklet);
 
 	if (qdio->adapter->ccw_device)
 		qdio_free(qdio->adapter->ccw_device);
@@ -520,8 +561,11 @@ int zfcp_qdio_setup(struct zfcp_adapter *adapter)
 
 	spin_lock_init(&qdio->req_q_lock);
 	spin_lock_init(&qdio->stat_lock);
+	timer_setup(&qdio->request_timer, zfcp_qdio_request_timer, 0);
 	tasklet_setup(&qdio->irq_tasklet, zfcp_qdio_irq_tasklet);
+	tasklet_setup(&qdio->request_tasklet, zfcp_qdio_request_tasklet);
 	tasklet_disable(&qdio->irq_tasklet);
+	tasklet_disable(&qdio->request_tasklet);
 
 	adapter->qdio = qdio;
 	return 0;

drivers/s390/scsi/zfcp_qdio.h

@@ -30,6 +30,9 @@
  * @req_q_util: used for accounting
  * @req_q_full: queue full incidents
  * @req_q_wq: used to wait for SBAL availability
+ * @irq_tasklet: used for QDIO interrupt processing
+ * @request_tasklet: used for Request Queue completion processing
+ * @request_timer: used to trigger the Request Queue completion processing
  * @adapter: adapter used in conjunction with this qdio structure
  * @max_sbale_per_sbal: qdio limit per sbal
  * @max_sbale_per_req: qdio limit per request
@@ -46,6 +49,8 @@ struct zfcp_qdio {
 	atomic_t		req_q_full;
 	wait_queue_head_t	req_q_wq;
 	struct tasklet_struct	irq_tasklet;
+	struct tasklet_struct	request_tasklet;
+	struct timer_list	request_timer;
 	struct zfcp_adapter	*adapter;
 	u16			max_sbale_per_sbal;
 	u16			max_sbale_per_req;