[PATCH v3] Drivers: hv: vmbus: Expose counters for interrupts and full conditions

Kimberly Brown
2019-01-17T04:38:06Z

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

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>
---
Changes in v3:
- Used the outbound ring buffer spinlock to protect the the full
condition counters in set_channel_pending_send_size()
- Corrected the KernelVersion values for the new entries in
Documentation/ABI/stable/sysfs-bus-vmbus

Changes in v2:
- Added mailing lists to the cc list
- Removed the host to guest interrupt counters proposed in v1 because
they were not accurate
- Added full condition counters for the channel's outbound ring buffer

Documentation/ABI/stable/sysfs-bus-vmbus | 33 ++++++++++++++++++++
drivers/hv/ring_buffer.c | 14 ++++++++-
drivers/hv/vmbus_drv.c | 32 ++++++++++++++++++++
include/linux/hyperv.h | 38 ++++++++++++++++++++++++
4 files changed, 116 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/stable/sysfs-bus-vmbus b/Documentation/ABI/stable/sysfs-bus-vmbus
index 3fed8fdb873d..a0304c563467 100644
--- a/Documentation/ABI/stable/sysfs-bus-vmbus
+++ b/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: January 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: January 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: January 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: January 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
diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
index 1f1a55e07733..9e8b31ccc142 100644
--- a/drivers/hv/ring_buffer.c
+++ b/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);
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 403fee01572c..e291a7d3180c 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -1496,6 +1496,34 @@ 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", 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", 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", 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", 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)
{
@@ -1521,6 +1549,10 @@ 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
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index dcb6977afce9..7e5239123276 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -751,6 +751,27 @@ struct vmbus_channel {
u64 interrupts; /* Host to Guest interrupts */
u64 sig_events; /* Guest to Host events */

+ /* Interrupt counts for 2 types of Guest to Host interrupts */
+ u64 intr_in_full; /* in ring buffer, full to not full */
+ u64 intr_out_empty; /* out ring buffer, empty to not empty */
+
+ /*
+ * 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;
+ /*
+ * 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);
@@ -936,6 +957,23 @@ 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;
+
+ spin_lock_irqsave(&c->outbound.ring_lock, flags);
+
+ if (size) {
+ ++c->out_full_total;
+
+ if (!c->out_full_flag) {
+ ++c->out_full_first;
+ c->out_full_flag = true;
+ }
+ } else {
+ c->out_full_flag = false;
+ }
+
+ spin_unlock_irqrestore(&c->outbound.ring_lock, flags);
+
c->outbound.ring_buffer->pending_send_sz = size;
}

--
2.17.1