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>

2 files changed, 17 insertions, 0 deletions

diff --git a/block/accounting.c b/block/accounting.c
index 61de8ce..a941931 100644
--- a/block/accounting.c
+++ b/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;
+}
diff --git a/block/qapi.c b/block/qapi.c
index 6169a22..d20262d 100644
--- a/block/qapi.c
+++ b/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);
         }
     }