block: Add average I/O queue depth to BlockDeviceTimedStats

This patch adds two new fields to BlockDeviceTimedStats that track the
average number of pending read and write requests for a block device.

The values are calculated for the period of time defined for that
interval.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Message-id: fd31fef53e2714f2f30d59ed58ca2f67ec9ab926.1446044837.git.berto@igalia.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/accounting.c

@@ -143,3 +143,15 @@ int64_t block_acct_idle_time_ns(BlockAcctStats *stats)
 {
     return qemu_clock_get_ns(clock_type) - stats->last_access_time_ns;
 }
+
+double block_acct_queue_depth(BlockAcctTimedStats *stats,
+                              enum BlockAcctType type)
+{
+    uint64_t sum, elapsed;
+
+    assert(type < BLOCK_MAX_IOTYPE);
+
+    sum = timed_average_sum(&stats->latency[type], &elapsed);
+
+    return (double) sum / elapsed;
+}

block/qapi.c

@@ -402,6 +402,11 @@ static BlockStats *bdrv_query_stats(const BlockDriverState *bs,
             dev_stats->min_flush_latency_ns = timed_average_min(fl);
             dev_stats->max_flush_latency_ns = timed_average_max(fl);
             dev_stats->avg_flush_latency_ns = timed_average_avg(fl);
+
+            dev_stats->avg_rd_queue_depth =
+                block_acct_queue_depth(ts, BLOCK_ACCT_READ);
+            dev_stats->avg_wr_queue_depth =
+                block_acct_queue_depth(ts, BLOCK_ACCT_WRITE);
         }
     }
 

include/block/accounting.h

@@ -78,5 +78,7 @@ void block_acct_invalid(BlockAcctStats *stats, enum BlockAcctType type);
 void block_acct_merge_done(BlockAcctStats *stats, enum BlockAcctType type,
                            int num_requests);
 int64_t block_acct_idle_time_ns(BlockAcctStats *stats);
+double block_acct_queue_depth(BlockAcctTimedStats *stats,
+                              enum BlockAcctType type);
 
 #endif

include/qemu/timed-average.h

@@ -59,5 +59,6 @@ void timed_average_account(TimedAverage *ta, uint64_t value);
 uint64_t timed_average_min(TimedAverage *ta);
 uint64_t timed_average_avg(TimedAverage *ta);
 uint64_t timed_average_max(TimedAverage *ta);
+uint64_t timed_average_sum(TimedAverage *ta, uint64_t *elapsed);
 
 #endif

qapi/block-core.json

@@ -450,6 +450,12 @@
 # @avg_flush_latency_ns: Average latency of flush operations in the
 #                        defined interval, in nanoseconds.
 #
+# @avg_rd_queue_depth: Average number of pending read operations
+#                      in the defined interval.
+#
+# @avg_wr_queue_depth: Average number of pending write operations
+#                      in the defined interval.
+#
 # Since: 2.5
 ##
 
@@ -458,7 +464,8 @@
             'max_rd_latency_ns': 'int', 'avg_rd_latency_ns': 'int',
             'min_wr_latency_ns': 'int', 'max_wr_latency_ns': 'int',
             'avg_wr_latency_ns': 'int', 'min_flush_latency_ns': 'int',
-            'max_flush_latency_ns': 'int', 'avg_flush_latency_ns': 'int' } }
+            'max_flush_latency_ns': 'int', 'avg_flush_latency_ns': 'int',
+            'avg_rd_queue_depth': 'number', 'avg_wr_queue_depth': 'number' } }
 
 ##
 # @BlockDeviceStats:

qmp-commands.hx

@@ -2635,6 +2635,12 @@ Each json-object contain the following:
         - "avg_flush_latency_ns": average latency of flush operations
                                   in the defined interval, in
                                   nanoseconds (json-int)
+        - "avg_rd_queue_depth": average number of pending read
+                                operations in the defined interval
+                                (json-number)
+        - "avg_wr_queue_depth": average number of pending write
+                                operations in the defined interval
+                                (json-number).
 - "parent": Contains recursively the statistics of the underlying
             protocol (e.g. the host file for a qcow2 image). If there is
             no underlying protocol, this field is omitted

util/timed-average.c

@@ -120,8 +120,10 @@ void timed_average_init(TimedAverage *ta, QEMUClockType clock_type,
  * expiration time if that's the case.
  *
  * @ta: the TimedAverage structure
+ * @elapsed: if non-NULL, the elapsed time (in ns) within the current
+ *           window will be stored here
  */
-static void check_expirations(TimedAverage *ta)
+static void check_expirations(TimedAverage *ta, uint64_t *elapsed)
 {
     int64_t now = qemu_clock_get_ns(ta->clock_type);
     int i;
@@ -143,6 +145,12 @@ static void check_expirations(TimedAverage *ta)
     } else {
         ta->current = 1;
     }
+
+    /* Calculate the elapsed time within the current window */
+    if (elapsed) {
+        int64_t remaining = ta->windows[ta->current].expiration - now;
+        *elapsed = ta->period - remaining;
+    }
 }
 
 /* Account a value
@@ -153,7 +161,7 @@ static void check_expirations(TimedAverage *ta)
 void timed_average_account(TimedAverage *ta, uint64_t value)
 {
     int i;
-    check_expirations(ta);
+    check_expirations(ta, NULL);
 
     /* Do the accounting in both windows at the same time */
     for (i = 0; i < 2; i++) {
@@ -180,7 +188,7 @@ void timed_average_account(TimedAverage *ta, uint64_t value)
 uint64_t timed_average_min(TimedAverage *ta)
 {
     TimedAverageWindow *w;
-    check_expirations(ta);
+    check_expirations(ta, NULL);
     w = current_window(ta);
     return w->min < UINT64_MAX ? w->min : 0;
 }
@@ -193,7 +201,7 @@ uint64_t timed_average_min(TimedAverage *ta)
 uint64_t timed_average_avg(TimedAverage *ta)
 {
     TimedAverageWindow *w;
-    check_expirations(ta);
+    check_expirations(ta, NULL);
     w = current_window(ta);
     return w->count > 0 ? w->sum / w->count : 0;
 }
@@ -205,6 +213,19 @@ uint64_t timed_average_avg(TimedAverage *ta)
  */
 uint64_t timed_average_max(TimedAverage *ta)
 {
-    check_expirations(ta);
+    check_expirations(ta, NULL);
     return current_window(ta)->max;
 }
+
+/* Get the sum of all accounted values
+ * @ta:      the TimedAverage structure
+ * @elapsed: if non-NULL, the elapsed time (in ns) will be stored here
+ * @ret:     the sum of all accounted values
+ */
+uint64_t timed_average_sum(TimedAverage *ta, uint64_t *elapsed)
+{
+    TimedAverageWindow *w;
+    check_expirations(ta, elapsed);
+    w = current_window(ta);
+    return w->sum;
+}