block: Add idle_time_ns to BlockDeviceStats

This patch adds the new field 'idle_time_ns' to the BlockDeviceStats
structure, indicating the time that has passed since the previous I/O
operation.

It also adds the block_acct_idle_time_ns() call, to ensure that all
references to the clock type used for accounting are in the same
place. This will later allow us to use a different clock for iotests.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Message-id: 7d8cfcf931453e1a2443e6626e8c1edc347c7c8a.1446044837.git.berto@igalia.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

2 files changed, 15 insertions, 2 deletions

diff --git a/block/accounting.c b/block/accounting.c
index 6f4c0f12eb..d427fa8fb8 100644
--- a/block/accounting.c
+++ b/block/accounting.c
@@ -40,12 +40,15 @@ void block_acct_start(BlockAcctStats *stats, BlockAcctCookie *cookie,
 
 void block_acct_done(BlockAcctStats *stats, BlockAcctCookie *cookie)
 {
+    int64_t time_ns = qemu_clock_get_ns(clock_type);
+    int64_t latency_ns = time_ns - cookie->start_time_ns;
+
     assert(cookie->type < BLOCK_MAX_IOTYPE);
 
     stats->nr_bytes[cookie->type] += cookie->bytes;
     stats->nr_ops[cookie->type]++;
-    stats->total_time_ns[cookie->type] +=
-        qemu_clock_get_ns(clock_type) - cookie->start_time_ns;
+    stats->total_time_ns[cookie->type] += latency_ns;
+    stats->last_access_time_ns = time_ns;
 }
 
 
@@ -55,3 +58,8 @@ void block_acct_merge_done(BlockAcctStats *stats, enum BlockAcctType type,
     assert(type < BLOCK_MAX_IOTYPE);
     stats->merged[type] += num_requests;
 }
+
+int64_t block_acct_idle_time_ns(BlockAcctStats *stats)
+{
+    return qemu_clock_get_ns(clock_type) - stats->last_access_time_ns;
+}
diff --git a/block/qapi.c b/block/qapi.c
index 89d4274177..9799656761 100644
--- a/block/qapi.c
+++ b/block/qapi.c
@@ -357,6 +357,11 @@ static BlockStats *bdrv_query_stats(const BlockDriverState *bs,
         s->stats->wr_total_time_ns = stats->total_time_ns[BLOCK_ACCT_WRITE];
         s->stats->rd_total_time_ns = stats->total_time_ns[BLOCK_ACCT_READ];
         s->stats->flush_total_time_ns = stats->total_time_ns[BLOCK_ACCT_FLUSH];
+
+        s->stats->has_idle_time_ns = stats->last_access_time_ns > 0;
+        if (s->stats->has_idle_time_ns) {
+            s->stats->idle_time_ns = block_acct_idle_time_ns(stats);
+        }
     }
 
     s->stats->wr_highest_offset = bs->wr_highest_offset;