To support hierarchical stats, it's necessary to remember stats from
dead children. Add cfqg->dead_stats and make a dying cfqg transfer
its stats to the parent's dead-stats.
The transfer happens form ->pd_offline_fn() and it is possible that
there are some residual IOs completing afterwards. Currently, we lose
these stats. Given that cgroup removal isn't a very high frequency
operation and the amount of residual IOs on offline are likely to be
nil or small, this shouldn't be a big deal and the complexity needed
to handle residual IOs - another callback and rather elaborate
synchronization to reach and lock the matching q - doesn't seem
justified.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
block/cfq-iosched.c | 57 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 56 insertions(+), 1 deletion(-)
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index f8b34bb..4d75b79 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -289,7 +289,8 @@ struct cfq_group {
/* number of requests that are on the dispatch list or inside driver */
int dispatched;
struct cfq_ttime ttime;
- struct cfqg_stats stats;
+ struct cfqg_stats stats; /* stats for this cfqg */
+ struct cfqg_stats dead_stats; /* stats pushed from dead children */
};
struct cfq_io_cq {
@@ -709,6 +710,47 @@ static void cfqg_stats_reset(struct cfqg_stats *stats)
#endif
}
+/* @to += @from */
+static void cfqg_stats_merge(struct cfqg_stats *to, struct cfqg_stats *from)
+{
+ /* queued stats shouldn't be cleared */
+ blkg_rwstat_merge(&to->service_bytes, &from->service_bytes);
+ blkg_rwstat_merge(&to->serviced, &from->serviced);
+ blkg_rwstat_merge(&to->merged, &from->merged);
+ blkg_rwstat_merge(&to->service_time, &from->service_time);
+ blkg_rwstat_merge(&to->wait_time, &from->wait_time);
+ blkg_stat_merge(&from->time, &from->time);
+#ifdef CONFIG_DEBUG_BLK_CGROUP
+ blkg_stat_merge(&to->unaccounted_time, &from->unaccounted_time);
+ blkg_stat_merge(&to->avg_queue_size_sum, &from->avg_queue_size_sum);
+ blkg_stat_merge(&to->avg_queue_size_samples, &from->avg_queue_size_samples);
+ blkg_stat_merge(&to->dequeue, &from->dequeue);
+ blkg_stat_merge(&to->group_wait_time, &from->group_wait_time);
+ blkg_stat_merge(&to->idle_time, &from->idle_time);
+ blkg_stat_merge(&to->empty_time, &from->empty_time);
+#endif
+}
+
+/*
+ * Transfer @cfqg's stats to its parent's dead_stats so that the ancestors'
+ * recursive stats can still account for the amount used by this cfqg after
+ * it's gone.
+ */
+static void cfqg_stats_xfer_dead(struct cfq_group *cfqg)
+{
+ struct cfq_group *parent = cfqg_parent(cfqg);
+
+ lockdep_assert_held(cfqg_to_blkg(cfqg)->q->queue_lock);
+
+ if (unlikely(!parent))
+ return;
+
+ cfqg_stats_merge(&parent->dead_stats, &cfqg->stats);
+ cfqg_stats_merge(&parent->dead_stats, &cfqg->dead_stats);
+ cfqg_stats_reset(&cfqg->stats);
+ cfqg_stats_reset(&cfqg->dead_stats);
+}
+
#else /* CONFIG_CFQ_GROUP_IOSCHED */
static inline struct cfq_group *cfqg_parent(struct cfq_group *cfqg) { return NULL; }
@@ -1475,11 +1517,23 @@ static void cfq_pd_init(struct blkcg_gq *blkg)
cfqg->leaf_weight = blkg->blkcg->cfq_leaf_weight;
}
+static void cfq_pd_offline(struct blkcg_gq *blkg)
+{
+ /*
+ * @blkg is going offline and will be ignored by
+ * blkg_[rw]stat_recursive_sum(). Transfer stats to the parent so
+ * that they don't get lost. If IOs complete after this point, the
+ * stats for them will be lost. Oh well...
+ */
+ cfqg_stats_xfer_dead(blkg_to_cfqg(blkg));
+}
+
static void cfq_pd_reset_stats(struct blkcg_gq *blkg)
{
struct cfq_group *cfqg = blkg_to_cfqg(blkg);
cfqg_stats_reset(&cfqg->stats);
+ cfqg_stats_reset(&cfqg->dead_stats);
}
/*
@@ -4408,6 +4462,7 @@ static struct blkcg_policy blkcg_policy_cfq = {
.cftypes = cfq_blkcg_files,
.pd_init_fn = cfq_pd_init,
+ .pd_offline_fn = cfq_pd_offline,
.pd_reset_stats_fn = cfq_pd_reset_stats,
};
#endif
--
1.8.0.2
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