[PATCH V2 05/13] blk-throttling: detect inactive cgroup

[Shaohua Li]

We don't have a tree to maintain active cgroups. If a cgroup is inactive
for some time, it should be excluded from bandwidth calculation.
Otherwise we will only assign partial bandwidth to active cgroups,
active cgroups will dispatch less IO, the estimated queue bandwidth
drops, which will cause active cgroups dispatch even less IO.

Signed-off-by: Shaohua Li <shli@xxxxxx>
---
 block/blk-throttle.c | 79 ++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 74 insertions(+), 5 deletions(-)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index fafe9c2..43de1dc 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -18,6 +18,8 @@
 #define DFT_WEIGHT (100)
 #define SHARE_SHIFT (14)
 #define MAX_SHARE (1 << SHARE_SHIFT)
+/* must be less than the interval we update bandwidth */
+#define CGCHECK_TIME (msecs_to_jiffies(100))
 
 /* Max dispatch from a group in 1 round */
 static int throtl_grp_quantum = 8;
@@ -83,8 +85,11 @@ struct throtl_service_queue {
 	struct timer_list	pending_timer;	/* fires on first_pending_disptime */
 
 	unsigned int		weight; /* this queue's weight against siblings */
+	unsigned int		acting_weight; /* actual weight of the queue */
 	unsigned int		children_weight; /* children weight */
 	unsigned int		share; /* disk bandwidth share of the queue */
+
+	unsigned long active_timestamp;
 };
 
 enum tg_state_flags {
@@ -184,6 +189,7 @@ struct throtl_data
 	/* Work for dispatching throttled bios */
 	struct work_struct dispatch_work;
 	enum run_mode mode;
+	unsigned long last_check_timestamp;
 };
 
 static bool td_weight_based(struct throtl_data *td)
@@ -444,7 +450,7 @@ static void throtl_pd_init(struct blkg_policy_data *pd)
 	if (cgroup_subsys_on_dfl(io_cgrp_subsys) && blkg->parent)
 		sq->parent_sq = &blkg_to_tg(blkg->parent)->service_queue;
 	sq->weight = DFT_WEIGHT;
-	sq->parent_sq->children_weight += sq->weight;
+	sq->acting_weight = 0;
 	tg->td = td;
 }
 
@@ -483,8 +489,10 @@ static void throtl_pd_free(struct blkg_policy_data *pd)
 	struct throtl_grp *tg = pd_to_tg(pd);
 	struct throtl_service_queue *sq = &tg->service_queue;
 
-	if (sq->parent_sq)
-		sq->parent_sq->children_weight -= sq->weight;
+	if (sq->acting_weight && sq->parent_sq) {
+		sq->parent_sq->children_weight -= sq->acting_weight;
+		sq->acting_weight = 0;
+	}
 
 	del_timer_sync(&tg->service_queue.pending_timer);
 	kfree(tg);
@@ -1096,16 +1104,74 @@ static void tg_update_share(struct throtl_data *td, struct throtl_grp *tg)
 		child = blkg_to_tg(blkg);
 		sq = &child->service_queue;
 
-		if (!sq->parent_sq)
+		if (!sq->parent_sq || !sq->acting_weight)
 			continue;
 
 		sq->share = max_t(unsigned int,
-			sq->parent_sq->share * sq->weight /
+			sq->parent_sq->share * sq->acting_weight /
 				sq->parent_sq->children_weight,
 			1);
 	}
 }
 
+static void tg_update_active_time(struct throtl_grp *tg)
+{
+	struct throtl_service_queue *sq = &tg->service_queue;
+	unsigned long now = jiffies;
+
+	tg = NULL;
+	while (sq->parent_sq) {
+		sq->active_timestamp = now;
+		if (!sq->acting_weight) {
+			sq->acting_weight = sq->weight;
+			sq->parent_sq->children_weight += sq->acting_weight;
+			tg = sq_to_tg(sq);
+		}
+		sq = sq->parent_sq;
+	}
+
+	if (tg)
+		tg_update_share(tg->td, tg);
+}
+
+static void detect_inactive_cg(struct throtl_grp *tg)
+{
+	struct throtl_data *td = tg->td;
+	struct throtl_service_queue *sq = &tg->service_queue;
+	unsigned long now = jiffies;
+	struct cgroup_subsys_state *pos_css;
+	struct blkcg_gq *blkg;
+	bool update_share = false;
+
+	tg_update_active_time(tg);
+
+	if (time_before(now, td->last_check_timestamp + CGCHECK_TIME))
+		return;
+	td->last_check_timestamp = now;
+
+	blkg_for_each_descendant_post(blkg, pos_css, td->queue->root_blkg) {
+		tg = blkg_to_tg(blkg);
+		sq = &tg->service_queue;
+		/* '/' cgroup of cgroup2 */
+		if (cgroup_subsys_on_dfl(io_cgrp_subsys) &&
+		    !tg_to_blkg(tg)->parent)
+			continue;
+
+		if (sq->parent_sq &&
+		    time_before(sq->active_timestamp + CGCHECK_TIME, now) &&
+		    !(sq->nr_queued[READ] || sq->nr_queued[WRITE])) {
+			if (sq->acting_weight && sq->parent_sq) {
+				sq->parent_sq->children_weight -= sq->acting_weight;
+				sq->acting_weight = 0;
+				update_share = true;
+			}
+		}
+	}
+
+	if (update_share)
+		tg_update_share(td, NULL);
+}
+
 static void tg_dispatch_one_bio(struct throtl_grp *tg, bool rw)
 {
 	struct throtl_service_queue *sq = &tg->service_queue;
@@ -1186,6 +1252,7 @@ static int throtl_dispatch_tg(struct throtl_grp *tg)
 			break;
 	}
 	if (nr_reads + nr_writes) {
+		detect_inactive_cg(tg);
 		tg_update_perf(tg);
 	}
 
@@ -1639,6 +1706,7 @@ bool blk_throtl_bio(struct request_queue *q, struct blkcg_gq *blkg,
 
 	sq = &tg->service_queue;
 
+	detect_inactive_cg(tg);
 	while (true) {
 		/* throtl is FIFO - if bios are already queued, should queue */
 		if (sq->nr_queued[index])
@@ -1791,6 +1859,7 @@ int blk_throtl_init(struct request_queue *q)
 	throtl_service_queue_init(&td->service_queue);
 	td->service_queue.share = MAX_SHARE;
 	td->mode = MODE_NONE;
+	td->service_queue.acting_weight = DFT_WEIGHT;
 
 	q->td = td;
 	td->queue = q;
-- 
2.6.5