vmbus: add direct isr callback mode

Change the simple boolean batched_reading into a tri-value.
For future NAPI support in netvsc driver, the callback needs to
occur directly in interrupt handler.

Batched mode is also changed to disable host interrupts immediately
in interrupt routine (to avoid unnecessary host signals), and the
tasklet is rescheduled if more data is detected.

Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

4 files changed, 37 insertions, 26 deletions

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 2f6270d76b79..b2bb5aafaa2f 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -820,13 +820,6 @@ static void vmbus_onoffer(struct vmbus_channel_message_header *hdr)
 	}
 
 	/*
-	 * By default we setup state to enable batched
-	 * reading. A specific service can choose to
-	 * disable this prior to opening the channel.
-	 */
-	newchannel->batched_reading = true;
-
-	/*
 	 * Setup state for signalling the host.
 	 */
 	newchannel->sig_event = (struct hv_input_signal_event *)
diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index 27e72dc07e12..a8366fec1458 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -300,9 +300,7 @@ struct vmbus_channel *relid2channel(u32 relid)
 void vmbus_on_event(unsigned long data)
 {
 	struct vmbus_channel *channel = (void *) data;
-	void *arg;
-	bool read_state;
-	u32 bytes_to_read;
+	void (*callback_fn)(void *);
 
 	/*
 	 * A channel once created is persistent even when there
@@ -312,9 +310,13 @@ void vmbus_on_event(unsigned long data)
 	 * Thus, checking and invoking the driver specific callback takes
 	 * care of orderly unloading of the driver.
 	 */
-	if (channel->onchannel_callback != NULL) {
-		arg = channel->channel_callback_context;
-		read_state = channel->batched_reading;
+	callback_fn = READ_ONCE(channel->onchannel_callback);
+	if (unlikely(callback_fn == NULL))
+		return;
+
+	(*callback_fn)(channel->channel_callback_context);
+
+	if (channel->callback_mode == HV_CALL_BATCHED) {
 		/*
 		 * This callback reads the messages sent by the host.
 		 * We can optimize host to guest signaling by ensuring:
@@ -326,16 +328,11 @@ void vmbus_on_event(unsigned long data)
 		 *    state is set we check to see if additional packets are
 		 *    available to read. In this case we repeat the process.
 		 */
+		if (hv_end_read(&channel->inbound) != 0) {
+			hv_begin_read(&channel->inbound);
 
-		do {
-			if (read_state)
-				hv_begin_read(&channel->inbound);
-			channel->onchannel_callback(arg);
-			if (read_state)
-				bytes_to_read = hv_end_read(&channel->inbound);
-			else
-				bytes_to_read = 0;
-		} while (read_state && (bytes_to_read != 0));
+			tasklet_schedule(&channel->callback_event);
+		}
 	}
 }
 
diff --git a/drivers/hv/hv_util.c b/drivers/hv/hv_util.c
index 098cd3dc7db2..3042eaa13062 100644
--- a/drivers/hv/hv_util.c
+++ b/drivers/hv/hv_util.c
@@ -435,8 +435,7 @@ static int util_probe(struct hv_device *dev,
 	 * Turn off batched reading for all util drivers before we open the
 	 * channel.
 	 */
-
-	set_channel_read_state(dev->channel, false);
+	set_channel_read_mode(dev->channel, HV_CALL_DIRECT);
 
 	hv_set_drvdata(dev, srv);
 
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index eaf1a10b0245..f7f6b9144b07 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -887,6 +887,18 @@ msg_handled:
 
 
 /*
+ * Direct callback for channels using other deferred processing
+ */
+static void vmbus_channel_isr(struct vmbus_channel *channel)
+{
+	void (*callback_fn)(void *);
+
+	callback_fn = READ_ONCE(channel->onchannel_callback);
+	if (likely(callback_fn != NULL))
+		(*callback_fn)(channel->channel_callback_context);
+}
+
+/*
  * Schedule all channels with events pending
  */
 static void vmbus_chan_sched(struct hv_per_cpu_context *hv_cpu)
@@ -927,9 +939,19 @@ static void vmbus_chan_sched(struct hv_per_cpu_context *hv_cpu)
 
 		/* Find channel based on relid */
 		list_for_each_entry(channel, &hv_cpu->chan_list, percpu_list) {
-			if (channel->offermsg.child_relid == relid) {
-				tasklet_schedule(&channel->callback_event);
+			if (channel->offermsg.child_relid != relid)
+				continue;
+
+			switch (channel->callback_mode) {
+			case HV_CALL_ISR:
+				vmbus_channel_isr(channel);
 				break;
+
+			case HV_CALL_BATCHED:
+				hv_begin_read(&channel->inbound);
+				/* fallthrough */
+			case HV_CALL_DIRECT:
+				tasklet_schedule(&channel->callback_event);
 			}
 		}
 	}