bdev: add tracking for time spent processing I/O.

Two extra fields are added to the iostat rpc.
1. io_time. The amount of time since queue depth tracking was
enabled that has been spent on I/O processing.
2. weighted_io_time. Incremented each time this bdev's queue depth is
polled by the amount of time spent processing I/O since the last polling
event times the measured queue depth.

Change-Id: Ie70489ec24dee83f3eeac8f4f813ec7074ff458f
Signed-off-by: Seth Howell <seth.howell@intel.com>
Reviewed-on: https://review.gerrithub.io/419031
Chandler-Test-Pool: SPDK Automated Test System <sys_sgsw@intel.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>

include/spdk/bdev.h

@@ -430,6 +430,40 @@ spdk_bdev_get_qd_sampling_period(const struct spdk_bdev *bdev);
  */
 void spdk_bdev_set_qd_sampling_period(struct spdk_bdev *bdev, uint64_t period);
 
+/**
+ * Get the time spent processing IO for this device.
+ *
+ * This value is dependent upon the queue depth sampling period and is
+ * incremented at sampling time by the sampling period only if the measured
+ * queue depth is greater than 0.
+ *
+ * The disk utilization can be calculated by the following formula:
+ * disk_util = (io_time_2 - io_time_1) / elapsed_time.
+ * The user is responsible for tracking the elapsed time between two measurements.
+ *
+ * \param bdev Block device to query.
+ *
+ * \return The io time for this device in microseconds.
+ */
+uint64_t spdk_bdev_get_io_time(const struct spdk_bdev *bdev);
+
+/**
+ * Get the weighted IO processing time for this bdev.
+ *
+ * This value is dependent upon the queue depth sampling period and is
+ * equal to the time spent reading from or writing to a device times
+ * the measured queue depth during each sampling period.
+ *
+ * The average queue depth can be calculated by the following formula:
+ * queue_depth = (weighted_io_time_2 - weighted_io_time_1) / elapsed_time.
+ * The user is responsible for tracking the elapsed time between two measurements.
+ *
+ * \param bdev Block device to query.
+ *
+ * \return The weighted io time for this device in microseconds.
+ */
+uint64_t spdk_bdev_get_weighted_io_time(const struct spdk_bdev *bdev);
+
 /**
  * Obtain an I/O channel for the block device opened by the specified
  * descriptor. I/O channels are bound to threads, so the resulting I/O

include/spdk/bdev_module.h

@@ -318,6 +318,12 @@ struct spdk_bdev {
 		/** queue depth as calculated the last time the telemetry poller checked. */
 		uint64_t measured_queue_depth;
 
+		/** most recent value of ticks spent performing I/O. Used to calculate the weighted time doing I/O */
+		uint64_t io_time;
+
+		/** weighted time performing I/O. Equal to measured_queue_depth * period */
+		uint64_t weighted_io_time;
+
 	} internal;
 };
 

lib/bdev/bdev.c

@@ -1641,12 +1641,28 @@ spdk_bdev_get_qd_sampling_period(const struct spdk_bdev *bdev)
 	return bdev->internal.period;
 }
 
+uint64_t
+spdk_bdev_get_weighted_io_time(const struct spdk_bdev *bdev)
+{
+	return bdev->internal.weighted_io_time;
+}
+
+uint64_t
+spdk_bdev_get_io_time(const struct spdk_bdev *bdev)
+{
+	return bdev->internal.io_time;
+}
+
 static void
 _calculate_measured_qd_cpl(struct spdk_io_channel_iter *i, int status)
 {
 	struct spdk_bdev *bdev = spdk_io_channel_iter_get_ctx(i);
 
 	bdev->internal.measured_queue_depth = bdev->internal.temporary_queue_depth;
+
+	if (bdev->internal.measured_queue_depth) {
+		bdev->internal.weighted_io_time += bdev->internal.period * bdev->internal.measured_queue_depth;
+	}
 }
 
 static void

lib/bdev/rpc/bdev_rpc.c

@@ -88,6 +88,12 @@ spdk_rpc_get_bdevs_iostat_cb(struct spdk_bdev *bdev,
 
 			spdk_json_write_name(w, "queue_depth");
 			spdk_json_write_uint64(w, spdk_bdev_get_qd(bdev));
+
+			spdk_json_write_name(w, "io_time");
+			spdk_json_write_uint64(w, spdk_bdev_get_io_time(bdev));
+
+			spdk_json_write_name(w, "weighted_io_time");
+			spdk_json_write_uint64(w, spdk_bdev_get_weighted_io_time(bdev));
 		}
 
 		spdk_json_write_object_end(w);