blkio: Add io_queued and avg_queue_size stats

These stats are useful for getting a feel for the queue depth of the cgroup,
i.e., how filled up its queues are at a given instant and over the existence of
the cgroup. This ability is useful when debugging problems in the wild as it
helps understand the application's IO pattern w/o having to read through the
userspace code (coz its tedious or just not available) or w/o the ability
to run blktrace (since you may not have root access and/or not want to disturb
performance).

Signed-off-by: Divyesh Shah<dpshah@google.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

3 files changed, 123 insertions, 6 deletions

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index d23b538858ce..1e0c4970b35d 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -81,6 +81,71 @@ static void blkio_add_stat(uint64_t *stat, uint64_t add, bool direction,
                 stat[BLKIO_STAT_ASYNC] += add;
 }
 
+/*
+ * Decrements the appropriate stat variable if non-zero depending on the
+ * request type. Panics on value being zero.
+ * This should be called with the blkg->stats_lock held.
+ */
+static void blkio_check_and_dec_stat(uint64_t *stat, bool direction, bool sync)
+{
+        if (direction) {
+                BUG_ON(stat[BLKIO_STAT_WRITE] == 0);
+                stat[BLKIO_STAT_WRITE]--;
+        } else {
+                BUG_ON(stat[BLKIO_STAT_READ] == 0);
+                stat[BLKIO_STAT_READ]--;
+        }
+        if (sync) {
+                BUG_ON(stat[BLKIO_STAT_SYNC] == 0);
+                stat[BLKIO_STAT_SYNC]--;
+        } else {
+                BUG_ON(stat[BLKIO_STAT_ASYNC] == 0);
+                stat[BLKIO_STAT_ASYNC]--;
+        }
+}
+
+#ifdef CONFIG_DEBUG_BLK_CGROUP
+void blkiocg_update_set_active_queue_stats(struct blkio_group *blkg)
+{
+        unsigned long flags;
+        struct blkio_group_stats *stats;
+
+        spin_lock_irqsave(&blkg->stats_lock, flags);
+        stats = &blkg->stats;
+        stats->avg_queue_size_sum +=
+                        stats->stat_arr[BLKIO_STAT_QUEUED][BLKIO_STAT_READ] +
+                        stats->stat_arr[BLKIO_STAT_QUEUED][BLKIO_STAT_WRITE];
+        stats->avg_queue_size_samples++;
+        spin_unlock_irqrestore(&blkg->stats_lock, flags);
+}
+EXPORT_SYMBOL_GPL(blkiocg_update_set_active_queue_stats);
+#endif
+
+void blkiocg_update_request_add_stats(struct blkio_group *blkg,
+                        struct blkio_group *curr_blkg, bool direction,
+                        bool sync)
+{
+        unsigned long flags;
+
+        spin_lock_irqsave(&blkg->stats_lock, flags);
+        blkio_add_stat(blkg->stats.stat_arr[BLKIO_STAT_QUEUED], 1, direction,
+                        sync);
+        spin_unlock_irqrestore(&blkg->stats_lock, flags);
+}
+EXPORT_SYMBOL_GPL(blkiocg_update_request_add_stats);
+
+void blkiocg_update_request_remove_stats(struct blkio_group *blkg,
+                                                bool direction, bool sync)
+{
+        unsigned long flags;
+
+        spin_lock_irqsave(&blkg->stats_lock, flags);
+        blkio_check_and_dec_stat(blkg->stats.stat_arr[BLKIO_STAT_QUEUED],
+                                        direction, sync);
+        spin_unlock_irqrestore(&blkg->stats_lock, flags);
+}
+EXPORT_SYMBOL_GPL(blkiocg_update_request_remove_stats);
+
 void blkiocg_update_timeslice_used(struct blkio_group *blkg, unsigned long time)
 {
         unsigned long flags;
@@ -253,14 +318,18 @@ blkiocg_reset_stats(struct cgroup *cgroup, struct cftype *cftype, u64 val)
         struct blkio_cgroup *blkcg;
         struct blkio_group *blkg;
         struct hlist_node *n;
-        struct blkio_group_stats *stats;
+        uint64_t queued[BLKIO_STAT_TOTAL];
+        int i;
 
         blkcg = cgroup_to_blkio_cgroup(cgroup);
         spin_lock_irq(&blkcg->lock);
         hlist_for_each_entry(blkg, n, &blkcg->blkg_list, blkcg_node) {
                 spin_lock(&blkg->stats_lock);
-                stats = &blkg->stats;
-                memset(stats, 0, sizeof(struct blkio_group_stats));
+                for (i = 0; i < BLKIO_STAT_TOTAL; i++)
+                        queued[i] = blkg->stats.stat_arr[BLKIO_STAT_QUEUED][i];
+                memset(&blkg->stats, 0, sizeof(struct blkio_group_stats));
+                for (i = 0; i < BLKIO_STAT_TOTAL; i++)
+                        blkg->stats.stat_arr[BLKIO_STAT_QUEUED][i] = queued[i];
                 spin_unlock(&blkg->stats_lock);
         }
         spin_unlock_irq(&blkcg->lock);
@@ -323,6 +392,15 @@ static uint64_t blkio_get_stat(struct blkio_group *blkg,
                 return blkio_fill_stat(key_str, MAX_KEY_LEN - 1,
                                         blkg->stats.sectors, cb, dev);
 #ifdef CONFIG_DEBUG_BLK_CGROUP
+        if (type == BLKIO_STAT_AVG_QUEUE_SIZE) {
+                uint64_t sum = blkg->stats.avg_queue_size_sum;
+                uint64_t samples = blkg->stats.avg_queue_size_samples;
+                if (samples)
+                        do_div(sum, samples);
+                else
+                        sum = 0;
+                return blkio_fill_stat(key_str, MAX_KEY_LEN - 1, sum, cb, dev);
+        }
         if (type == BLKIO_STAT_DEQUEUE)
                 return blkio_fill_stat(key_str, MAX_KEY_LEN - 1,
                                         blkg->stats.dequeue, cb, dev);
@@ -376,8 +454,10 @@ SHOW_FUNCTION_PER_GROUP(io_serviced, BLKIO_STAT_SERVICED, 1);
 SHOW_FUNCTION_PER_GROUP(io_service_time, BLKIO_STAT_SERVICE_TIME, 1);
 SHOW_FUNCTION_PER_GROUP(io_wait_time, BLKIO_STAT_WAIT_TIME, 1);
 SHOW_FUNCTION_PER_GROUP(io_merged, BLKIO_STAT_MERGED, 1);
+SHOW_FUNCTION_PER_GROUP(io_queued, BLKIO_STAT_QUEUED, 1);
 #ifdef CONFIG_DEBUG_BLK_CGROUP
 SHOW_FUNCTION_PER_GROUP(dequeue, BLKIO_STAT_DEQUEUE, 0);
+SHOW_FUNCTION_PER_GROUP(avg_queue_size, BLKIO_STAT_AVG_QUEUE_SIZE, 0);
 #endif
 #undef SHOW_FUNCTION_PER_GROUP
 
@@ -425,14 +505,22 @@ struct cftype blkio_files[] = {
                 .read_map = blkiocg_io_merged_read,
         },
         {
+                .name = "io_queued",
+                .read_map = blkiocg_io_queued_read,
+        },
+        {
                 .name = "reset_stats",
                 .write_u64 = blkiocg_reset_stats,
         },
 #ifdef CONFIG_DEBUG_BLK_CGROUP
-       {
+        {
+                .name = "avg_queue_size",
+                .read_map = blkiocg_avg_queue_size_read,
+        },
+        {
                 .name = "dequeue",
                 .read_map = blkiocg_dequeue_read,
-       },
+        },
 #endif
 };
 
diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 470a29db6bec..bea7f3b9a88e 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -36,10 +36,13 @@ enum stat_type {
         BLKIO_STAT_WAIT_TIME,
         /* Number of IOs merged */
         BLKIO_STAT_MERGED,
+        /* Number of IOs queued up */
+        BLKIO_STAT_QUEUED,
         /* All the single valued stats go below this */
         BLKIO_STAT_TIME,
         BLKIO_STAT_SECTORS,
 #ifdef CONFIG_DEBUG_BLK_CGROUP
+        BLKIO_STAT_AVG_QUEUE_SIZE,
         BLKIO_STAT_DEQUEUE
 #endif
 };
@@ -63,8 +66,12 @@ struct blkio_group_stats {
         /* total disk time and nr sectors dispatched by this group */
         uint64_t time;
         uint64_t sectors;
-        uint64_t stat_arr[BLKIO_STAT_MERGED + 1][BLKIO_STAT_TOTAL];
+        uint64_t stat_arr[BLKIO_STAT_QUEUED + 1][BLKIO_STAT_TOTAL];