qapi: add block latency histogram interface

Set (and clear) histograms through new command
block-latency-histogram-set and show new statistics in
query-blockstats results.

For now, the command is marked experimental with prefix 'x-',
to gain experience with the interface without being stuck
with design decisions.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20180309165212.97144-3-vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
[eblake: fix typos, mention x- prefix in commit message]
Signed-off-by: Eric Blake <eblake@redhat.com>

1 files changed, 41 insertions, 0 deletions

diff --git a/block/qapi.c b/block/qapi.c
index f2e0aa2..04c6fc6 100644
--- a/block/qapi.c
+++ b/block/qapi.c
@@ -394,6 +394,37 @@ static void bdrv_query_info(BlockBackend *blk, BlockInfo **p_info,
     qapi_free_BlockInfo(info);
 }
 
+static uint64List *uint64_list(uint64_t *list, int size)
+{
+    int i;
+    uint64List *out_list = NULL;
+    uint64List **pout_list = &out_list;
+
+    for (i = 0; i < size; i++) {
+        uint64List *entry = g_new(uint64List, 1);
+        entry->value = list[i];
+        *pout_list = entry;
+        pout_list = &entry->next;
+    }
+
+    *pout_list = NULL;
+
+    return out_list;
+}
+
+static void bdrv_latency_histogram_stats(BlockLatencyHistogram *hist,
+                                         bool *not_null,
+                                         BlockLatencyHistogramInfo **info)
+{
+    *not_null = hist->bins != NULL;
+    if (*not_null) {
+        *info = g_new0(BlockLatencyHistogramInfo, 1);
+
+        (*info)->boundaries = uint64_list(hist->boundaries, hist->nbins - 1);
+        (*info)->bins = uint64_list(hist->bins, hist->nbins);
+    }
+}
+
 static void bdrv_query_blk_stats(BlockDeviceStats *ds, BlockBackend *blk)
 {
     BlockAcctStats *stats = blk_get_stats(blk);
@@ -459,6 +490,16 @@ static void bdrv_query_blk_stats(BlockDeviceStats *ds, BlockBackend *blk)
         dev_stats->avg_wr_queue_depth =
             block_acct_queue_depth(ts, BLOCK_ACCT_WRITE);
     }
+
+    bdrv_latency_histogram_stats(&stats->latency_histogram[BLOCK_ACCT_READ],
+                                 &ds->has_x_rd_latency_histogram,
+                                 &ds->x_rd_latency_histogram);
+    bdrv_latency_histogram_stats(&stats->latency_histogram[BLOCK_ACCT_WRITE],
+                                 &ds->has_x_wr_latency_histogram,
+                                 &ds->x_wr_latency_histogram);
+    bdrv_latency_histogram_stats(&stats->latency_histogram[BLOCK_ACCT_FLUSH],
+                                 &ds->has_x_flush_latency_histogram,
+                                 &ds->x_flush_latency_histogram);
 }
 
 static BlockStats *bdrv_query_bds_stats(BlockDriverState *bs,