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>

1 files changed, 46 insertions, 0 deletions

diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index d5678a0fe598..64698ec8f2ac 100644
--- a/include/linux/hyperv.h
+++ b/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;
 }