Drivers: hv: vmbus: Expose counters for interrupts and full conditions

Counter values for per-channel interrupts and ring buffer full
conditions are useful for investigating performance.

Expose counters in sysfs for 2 types of guest to host interrupts:
1) Interrupts caused by the channel's outbound ring buffer transitioning
from empty to not empty
2) Interrupts caused by the channel's inbound ring buffer transitioning
from full to not full while a packet is waiting for enough buffer space to
become available

Expose 2 counters in sysfs for the number of times that write operations
encountered a full outbound ring buffer:
1) The total number of write operations that encountered a full
condition
2) The number of write operations that were the first to encounter a
full condition

Increment the outbound full condition counters in the
hv_ringbuffer_write() function because, for most drivers, a full
outbound ring buffer is detected in that function. Also increment the
outbound full condition counters in the set_channel_pending_send_size()
function. In the hv_sock driver, a full outbound ring buffer is detected
and set_channel_pending_send_size() is called before
hv_ringbuffer_write() is called.

I tested this patch by confirming that the sysfs files were created and
observing the counter values. The values seemed to increase by a
reasonable amount when the Hyper-v related drivers were in use.

Signed-off-by: Kimberly Brown <kimbrownkd@gmail.com>
Reviewed-by:  Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Documentation/ABI/stable/sysfs-bus-vmbus

@@ -146,3 +146,36 @@ KernelVersion:	4.16
 Contact:	Stephen Hemminger <sthemmin@microsoft.com>
 Description:	Binary file created by uio_hv_generic for ring buffer
 Users:		Userspace drivers
+
+What:           /sys/bus/vmbus/devices/<UUID>/channels/<N>/intr_in_full
+Date:           February 2019
+KernelVersion:  5.0
+Contact:        Michael Kelley <mikelley@microsoft.com>
+Description:    Number of guest to host interrupts caused by the inbound ring
+		buffer transitioning from full to not full while a packet is
+		waiting for buffer space to become available
+Users:          Debugging tools
+
+What:           /sys/bus/vmbus/devices/<UUID>/channels/<N>/intr_out_empty
+Date:           February 2019
+KernelVersion:  5.0
+Contact:        Michael Kelley <mikelley@microsoft.com>
+Description:    Number of guest to host interrupts caused by the outbound ring
+		buffer transitioning from empty to not empty
+Users:          Debugging tools
+
+What:           /sys/bus/vmbus/devices/<UUID>/channels/<N>/out_full_first
+Date:           February 2019
+KernelVersion:  5.0
+Contact:        Michael Kelley <mikelley@microsoft.com>
+Description:    Number of write operations that were the first to encounter an
+		outbound ring buffer full condition
+Users:          Debugging tools
+
+What:           /sys/bus/vmbus/devices/<UUID>/channels/<N>/out_full_total
+Date:           February 2019
+KernelVersion:  5.0
+Contact:        Michael Kelley <mikelley@microsoft.com>
+Description:    Total number of write operations that encountered an outbound
+		ring buffer full condition
+Users:          Debugging tools

drivers/hv/ring_buffer.c

@@ -74,8 +74,10 @@ static void hv_signal_on_write(u32 old_write, struct vmbus_channel *channel)
 	 * This is the only case we need to signal when the
 	 * ring transitions from being empty to non-empty.
 	 */
-	if (old_write == READ_ONCE(rbi->ring_buffer->read_index))
+	if (old_write == READ_ONCE(rbi->ring_buffer->read_index)) {
+		++channel->intr_out_empty;
 		vmbus_setevent(channel);
+	}
 }
 
 /* Get the next write location for the specified ring buffer. */
@@ -272,10 +274,19 @@ int hv_ringbuffer_write(struct vmbus_channel *channel,
 	 * is empty since the read index == write index.
 	 */
 	if (bytes_avail_towrite <= totalbytes_towrite) {
+		++channel->out_full_total;
+
+		if (!channel->out_full_flag) {
+			++channel->out_full_first;
+			channel->out_full_flag = true;
+		}
+
 		spin_unlock_irqrestore(&outring_info->ring_lock, flags);
 		return -EAGAIN;
 	}
 
+	channel->out_full_flag = false;
+
 	/* Write to the ring buffer */
 	next_write_location = hv_get_next_write_location(outring_info);
 
@@ -530,6 +541,7 @@ void hv_pkt_iter_close(struct vmbus_channel *channel)
 	if (curr_write_sz <= pending_sz)
 		return;
 
+	++channel->intr_in_full;
 	vmbus_setevent(channel);
 }
 EXPORT_SYMBOL_GPL(hv_pkt_iter_close);

drivers/hv/vmbus_drv.c

@@ -1484,6 +1484,38 @@ static ssize_t channel_events_show(const struct vmbus_channel *channel, char *bu
 }
 static VMBUS_CHAN_ATTR(events, S_IRUGO, channel_events_show, NULL);
 
+static ssize_t channel_intr_in_full_show(const struct vmbus_channel *channel,
+					 char *buf)
+{
+	return sprintf(buf, "%llu\n",
+		       (unsigned long long)channel->intr_in_full);
+}
+static VMBUS_CHAN_ATTR(intr_in_full, 0444, channel_intr_in_full_show, NULL);
+
+static ssize_t channel_intr_out_empty_show(const struct vmbus_channel *channel,
+					   char *buf)
+{
+	return sprintf(buf, "%llu\n",
+		       (unsigned long long)channel->intr_out_empty);
+}
+static VMBUS_CHAN_ATTR(intr_out_empty, 0444, channel_intr_out_empty_show, NULL);
+
+static ssize_t channel_out_full_first_show(const struct vmbus_channel *channel,
+					   char *buf)
+{
+	return sprintf(buf, "%llu\n",
+		       (unsigned long long)channel->out_full_first);
+}
+static VMBUS_CHAN_ATTR(out_full_first, 0444, channel_out_full_first_show, NULL);
+
+static ssize_t channel_out_full_total_show(const struct vmbus_channel *channel,
+					   char *buf)
+{
+	return sprintf(buf, "%llu\n",
+		       (unsigned long long)channel->out_full_total);
+}
+static VMBUS_CHAN_ATTR(out_full_total, 0444, channel_out_full_total_show, NULL);
+
 static ssize_t subchannel_monitor_id_show(const struct vmbus_channel *channel,
 					  char *buf)
 {
@@ -1509,6 +1541,10 @@ static struct attribute *vmbus_chan_attrs[] = {
 	&chan_attr_latency.attr,
 	&chan_attr_interrupts.attr,
 	&chan_attr_events.attr,
+	&chan_attr_intr_in_full.attr,
+	&chan_attr_intr_out_empty.attr,
+	&chan_attr_out_full_first.attr,
+	&chan_attr_out_full_total.attr,
 	&chan_attr_monitor_id.attr,
 	&chan_attr_subchannel_id.attr,
 	NULL

include/linux/hyperv.h

@@ -751,6 +751,19 @@ struct vmbus_channel {
 	u64	interrupts;	/* Host to Guest interrupts */
 	u64	sig_events;	/* Guest to Host events */
 
+	/*
+	 * Guest to host interrupts caused by the outbound ring buffer changing
+	 * from empty to not empty.
+	 */
+	u64 intr_out_empty;
+
+	/*
+	 * Indicates that a full outbound ring buffer was encountered. The flag
+	 * is set to true when a full outbound ring buffer is encountered and
+	 * set to false when a write to the outbound ring buffer is completed.
+	 */
+	bool out_full_flag;
+
 	/* Channel callback's invoked in softirq context */
 	struct tasklet_struct callback_event;
 	void (*onchannel_callback)(void *context);
@@ -903,6 +916,24 @@ struct vmbus_channel {
 	 * vmbus_connection.work_queue and hang: see vmbus_process_offer().
 	 */
 	struct work_struct add_channel_work;
+
+	/*
+	 * Guest to host interrupts caused by the inbound ring buffer changing
+	 * from full to not full while a packet is waiting.
+	 */
+	u64 intr_in_full;
+
+	/*
+	 * The total number of write operations that encountered a full
+	 * outbound ring buffer.
+	 */
+	u64 out_full_total;
+
+	/*
+	 * The number of write operations that were the first to encounter a
+	 * full outbound ring buffer.
+	 */
+	u64 out_full_first;
 };
 
 static inline bool is_hvsock_channel(const struct vmbus_channel *c)
@@ -936,6 +967,21 @@ static inline void *get_per_channel_state(struct vmbus_channel *c)
 static inline void set_channel_pending_send_size(struct vmbus_channel *c,
 						 u32 size)
 {
+	unsigned long flags;
+
+	if (size) {
+		spin_lock_irqsave(&c->outbound.ring_lock, flags);
+		++c->out_full_total;
+
+		if (!c->out_full_flag) {
+			++c->out_full_first;
+			c->out_full_flag = true;
+		}
+		spin_unlock_irqrestore(&c->outbound.ring_lock, flags);
+	} else {
+		c->out_full_flag = false;
+	}
+
 	c->outbound.ring_buffer->pending_send_sz = size;
 }