[Qemu-devel] [PATCH V3 for-1.6 5/5] block: Add throttling percentage metrics.

["Benoît Canet" <benoit@irqsave.net>]

This metrics show how many percent of the time I/Os are put on hold by the
throttling algorithm.
This metric could be used by system administrators or cloud stack developpers
to decide when the throttling settings must be changed.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
---
 block.c                   |   27 ++++++++++++++++++++++++++-
 block/qapi.c              |    4 ++++
 hmp.c                     |    6 ++++--
 include/block/block_int.h |    2 ++
 qapi-schema.json          |    4 +++-
 5 files changed, 39 insertions(+), 4 deletions(-)

diff --git a/block.c b/block.c
index bb4f8e4..6bb8570 100644
--- a/block.c
+++ b/block.c
@@ -118,12 +118,21 @@ int is_windows_drive(const char *filename)
 #endif
 
 /* throttling disk I/O limits */
+static void bdrv_reset_throttling_metrics(BlockDriverState *bs)
+{
+    /* iddle -> reset values */
+    bs->throttling_percentage = 0;
+    bs->full_since = 0;
+}
+
 void bdrv_io_limits_disable(BlockDriverState *bs)
 {
     bs->io_limits_enabled = false;
 
     while (qemu_co_enter_next(&bs->throttled_reqs)) {
     }
+
+    bdrv_reset_throttling_metrics(bs);
 }
 
 static void bdrv_make_bps_buckets_leak(BlockDriverState *bs, int64_t delta)
@@ -213,7 +222,8 @@ static void bdrv_make_iops_buckets_leak(BlockDriverState *bs, int64_t delta)
 static void bdrv_leak_if_needed(BlockDriverState *bs)
 {
     int64_t now;
-    int64_t delta;
+    int64_t delta; /* the delta that would be ideally the timer period */
+    int64_t delta_full; /* the delta where the bucket is full */
 
     if (!bs->must_leak) {
         return;
@@ -223,6 +233,14 @@ static void bdrv_leak_if_needed(BlockDriverState *bs)
 
     now = qemu_get_clock_ns(rt_clock);
     delta = now - bs->previous_leak;
+    /* compute throttle percentage reflecting how long IO are hold on average */
+    if (bs->full_since) {
+        delta_full = now - bs->full_since;
+        bs->throttling_percentage = (delta_full * 100) / delta;
+        bs->full_since = 0;
+    } else {
+        bs->throttling_percentage = 0;
+    }
     bs->previous_leak = now;
 
     bdrv_make_bps_buckets_leak(bs, delta);
@@ -260,6 +278,7 @@ static void bdrv_block_timer(void *opaque)
     /* disable throttling time on iddle for economy purpose */
     if (bdrv_throttling_is_iddle(bs)) {
         bdrv_block_timer_disable(bs);
+        bdrv_reset_throttling_metrics(bs);
         return;
     }
 
@@ -280,6 +299,7 @@ static void bdrv_block_timer_enable(BlockDriverState *bs)
 
     bs->block_timer = qemu_new_timer_ns(vm_clock, bdrv_block_timer, bs);
     bs->previous_leak = qemu_get_clock_ns(rt_clock);
+    bdrv_reset_throttling_metrics(bs);
     qemu_mod_timer(bs->block_timer,
                    qemu_get_clock_ns(vm_clock) +
                    BLOCK_IO_THROTTLE_PERIOD);
@@ -432,6 +452,11 @@ static void bdrv_io_limits_intercept(BlockDriverState *bs,
      * not full
      */
     while (bdrv_is_any_threshold_exceeded(bs, nb_sectors, is_write)) {
+        /* remember since when the code decided to block the first I/O */
+        if (qemu_co_queue_empty(&bs->throttled_reqs)) {
+            bs->full_since = qemu_get_clock_ns(rt_clock);
+        }
+
         bdrv_leak_if_needed(bs);
         qemu_co_queue_wait_insert_head(&bs->throttled_reqs);
         bdrv_leak_if_needed(bs);
diff --git a/block/qapi.c b/block/qapi.c
index f81081c..bd1c6af 100644
--- a/block/qapi.c
+++ b/block/qapi.c
@@ -263,6 +263,10 @@ void bdrv_query_info(BlockDriverState *bs,
                            bs->io_limits.iops_sector_count;
             info->inserted->iops_sector_count =
                            bs->io_limits.iops_sector_count;
+            info->inserted->has_throttling_percentage =
+                           bs->throttling_percentage;
+            info->inserted->throttling_percentage =
+                           bs->throttling_percentage;
         }
 
         bs0 = bs;
diff --git a/hmp.c b/hmp.c
index 3912305..9dc4862 100644
--- a/hmp.c
+++ b/hmp.c
@@ -348,7 +348,8 @@ void hmp_info_block(Monitor *mon, const QDict *qdict)
                             " iops_threshold=%" PRId64
                             " iops_rd_threshold=%" PRId64
                             " iops_wr_threshold=%" PRId64
-                            " iops_sector_count=%" PRId64 "\n",
+                            " iops_sector_count=%" PRId64
+                            " throttling_percentage=%" PRId64 "\n",
                             info->value->inserted->bps,
                             info->value->inserted->bps_rd,
                             info->value->inserted->bps_wr,
@@ -361,7 +362,8 @@ void hmp_info_block(Monitor *mon, const QDict *qdict)
                             info->value->inserted->iops_threshold,
                             info->value->inserted->iops_rd_threshold,
                             info->value->inserted->iops_wr_threshold,
-                            info->value->inserted->iops_sector_count);
+                            info->value->inserted->iops_sector_count,
+                            info->value->inserted->throttling_percentage);
         } else {
             monitor_printf(mon, " [not inserted]");
         }
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 74d7503..4487cd9 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -271,6 +271,8 @@ struct BlockDriverState {
     BlockIOLimit io_limits;
     BlockIOBaseValue leaky_buckets;
     int64_t      previous_leak;
+    int64_t      full_since;
+    int          throttling_percentage;
     bool         must_leak;
     CoQueue      throttled_reqs;
     QEMUTimer    *block_timer;
diff --git a/qapi-schema.json b/qapi-schema.json
index d579fda..14a02e7 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -783,6 +783,8 @@
 #
 # @iops_sector_count: #optional an I/O size in sector (Since 1.6)
 #
+# @throttling_percentage: #optional reflect throttling activity (Since 1.6)
+#
 # Since: 0.14.0
 #
 # Notes: This interface is only found in @BlockInfo.
@@ -797,7 +799,7 @@
             '*bps_threshold': 'int', '*bps_rd_threshold': 'int',
             '*bps_wr_threshold': 'int', '*iops_threshold': 'int',
             '*iops_rd_threshold': 'int', '*iops_wr_threshold': 'int',
-            '*iops_sector_count': 'int' } }
+            '*iops_sector_count': 'int', '*throttling_percentage': 'int' } }
 
 ##
 # @BlockDeviceIoStatus:
-- 
1.7.10.4