Drivers: hv: vmbus: Implement multi-channel support

Starting with Win8, the host supports multiple sub-channels for a given
device. As in the past, the initial channel offer specifies the device and
is associated with both the type and the instance GUIDs. For performance
critical devices, the host may support multiple sub-channels. The sub-channels
share the same type and instance GUID as the primary channel. The number of
sub-channels offerrred to the guest depends on the number of virtual CPUs
assigned to the guest. The guest can request the creation of these sub-channels
and once created and opened, the guest can distribute the traffic across all
the channels (the primary and the sub-channels). A request sent on a sub-channel
will have the response delivered on the same sub-channel.

At channel (sub-channel) creation we bind the channel interrupt to a CPU and
with this sub-channel support we will be able to spread the interrupt load
of a given device across all available CPUs.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 115 insertions, 4 deletions

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 21ef68934a20..0df75908200e 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -115,6 +115,9 @@ static struct vmbus_channel *alloc_channel(void)
 		return NULL;
 
 	spin_lock_init(&channel->inbound_lock);
+	spin_lock_init(&channel->sc_lock);
+
+	INIT_LIST_HEAD(&channel->sc_list);
 
 	channel->controlwq = create_workqueue("hv_vmbus_ctl");
 	if (!channel->controlwq) {
@@ -166,6 +169,7 @@ static void vmbus_process_rescind_offer(struct work_struct *work)
 						     struct vmbus_channel,
 						     work);
 	unsigned long flags;
+	struct vmbus_channel *primary_channel;
 	struct vmbus_channel_relid_released msg;
 
 	vmbus_device_unregister(channel->device_obj);
@@ -174,9 +178,16 @@ static void vmbus_process_rescind_offer(struct work_struct *work)
 	msg.header.msgtype = CHANNELMSG_RELID_RELEASED;
 	vmbus_post_msg(&msg, sizeof(struct vmbus_channel_relid_released));
 
-	spin_lock_irqsave(&vmbus_connection.channel_lock, flags);
-	list_del(&channel->listentry);
-	spin_unlock_irqrestore(&vmbus_connection.channel_lock, flags);
+	if (channel->primary_channel == NULL) {
+		spin_lock_irqsave(&vmbus_connection.channel_lock, flags);
+		list_del(&channel->listentry);
+		spin_unlock_irqrestore(&vmbus_connection.channel_lock, flags);
+	} else {
+		primary_channel = channel->primary_channel;
+		spin_lock_irqsave(&primary_channel->sc_lock, flags);
+		list_del(&channel->listentry);
+		spin_unlock_irqrestore(&primary_channel->sc_lock, flags);
+	}
 	free_channel(channel);
 }
 
@@ -228,6 +239,24 @@ static void vmbus_process_offer(struct work_struct *work)
 	spin_unlock_irqrestore(&vmbus_connection.channel_lock, flags);
 
 	if (!fnew) {
+		/*
+		 * Check to see if this is a sub-channel.
+		 */
+		if (newchannel->offermsg.offer.sub_channel_index != 0) {
+			/*
+			 * Process the sub-channel.
+			 */
+			newchannel->primary_channel = channel;
+			spin_lock_irqsave(&channel->sc_lock, flags);
+			list_add_tail(&newchannel->sc_list, &channel->sc_list);
+			spin_unlock_irqrestore(&channel->sc_lock, flags);
+			newchannel->state = CHANNEL_OPEN_STATE;
+			if (channel->sc_creation_callback != NULL)
+				channel->sc_creation_callback(newchannel);
+
+			return;
+		}
+
 		free_channel(newchannel);
 		return;
 	}
@@ -685,4 +714,86 @@ cleanup:
 	return ret;
 }
 
-/* eof */
+/*
+ * Retrieve the (sub) channel on which to send an outgoing request.
+ * When a primary channel has multiple sub-channels, we choose a
+ * channel whose VCPU binding is closest to the VCPU on which
+ * this call is being made.
+ */
+struct vmbus_channel *vmbus_get_outgoing_channel(struct vmbus_channel *primary)
+{
+	struct list_head *cur, *tmp;
+	int cur_cpu = hv_context.vp_index[smp_processor_id()];
+	struct vmbus_channel *cur_channel;
+	struct vmbus_channel *outgoing_channel = primary;
+	int cpu_distance, new_cpu_distance;
+
+	if (list_empty(&primary->sc_list))
+		return outgoing_channel;
+
+	list_for_each_safe(cur, tmp, &primary->sc_list) {
+		cur_channel = list_entry(cur, struct vmbus_channel, sc_list);
+		if (cur_channel->state != CHANNEL_OPENED_STATE)
+			continue;
+
+		if (cur_channel->target_vp == cur_cpu)
+			return cur_channel;
+
+		cpu_distance = ((outgoing_channel->target_vp > cur_cpu) ?
+				(outgoing_channel->target_vp - cur_cpu) :
+				(cur_cpu - outgoing_channel->target_vp));
+
+		new_cpu_distance = ((cur_channel->target_vp > cur_cpu) ?
+				(cur_channel->target_vp - cur_cpu) :
+				(cur_cpu - cur_channel->target_vp));
+
+		if (cpu_distance < new_cpu_distance)
+			continue;
+
+		outgoing_channel = cur_channel;
+	}
+
+	return outgoing_channel;
+}
+EXPORT_SYMBOL_GPL(vmbus_get_outgoing_channel);
+
+static void invoke_sc_cb(struct vmbus_channel *primary_channel)
+{
+	struct list_head *cur, *tmp;
+	struct vmbus_channel *cur_channel;
+
+	if (primary_channel->sc_creation_callback == NULL)
+		return;
+
+	list_for_each_safe(cur, tmp, &primary_channel->sc_list) {
+		cur_channel = list_entry(cur, struct vmbus_channel, sc_list);
+
+		primary_channel->sc_creation_callback(cur_channel);
+	}
+}
+
+void vmbus_set_sc_create_callback(struct vmbus_channel *primary_channel,
+				void (*sc_cr_cb)(struct vmbus_channel *new_sc))
+{
+	primary_channel->sc_creation_callback = sc_cr_cb;
+}
+EXPORT_SYMBOL_GPL(vmbus_set_sc_create_callback);
+
+bool vmbus_are_subchannels_present(struct vmbus_channel *primary)
+{
+	bool ret;
+
+	ret = !list_empty(&primary->sc_list);
+
+	if (ret) {
+		/*
+		 * Invoke the callback on sub-channel creation.
+		 * This will present a uniform interface to the
+		 * clients.
+		 */
+		invoke_sc_cb(primary);
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(vmbus_are_subchannels_present);