blk-iocost: add three debug stat - cost.wait, indebt and indelay

These are really cheap to collect and can be useful in debugging iocost
behavior. Add them as debug stats for now.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-iocost.c

@@ -452,6 +452,9 @@ struct iocg_pcpu_stat {
 
 struct iocg_stat {
 	u64				usage_us;
+	u64				wait_us;
+	u64				indebt_us;
+	u64				indelay_us;
 };
 
 /* per device-cgroup pair */
@@ -538,6 +541,9 @@ struct ioc_gq {
 	struct iocg_stat		last_stat;
 	u64				last_stat_abs_vusage;
 	u64				usage_delta_us;
+	u64				wait_since;
+	u64				indebt_since;
+	u64				indelay_since;
 
 	/* this iocg's depth in the hierarchy and ancestors including self */
 	int				level;
@@ -1303,9 +1309,15 @@ static bool iocg_kick_delay(struct ioc_gq *iocg, struct ioc_now *now)
 	}
 
 	if (delay >= MIN_DELAY) {
+		if (!iocg->indelay_since)
+			iocg->indelay_since = now->now;
 		blkcg_set_delay(blkg, delay * NSEC_PER_USEC);
 		return true;
 	} else {
+		if (iocg->indelay_since) {
+			iocg->local_stat.indelay_us += now->now - iocg->indelay_since;
+			iocg->indelay_since = 0;
+		}
 		iocg->delay = 0;
 		blkcg_clear_delay(blkg);
 		return false;
@@ -1325,8 +1337,10 @@ static void iocg_incur_debt(struct ioc_gq *iocg, u64 abs_cost,
 	 * Once in debt, debt handling owns inuse. @iocg stays at the minimum
 	 * inuse donating all of it share to others until its debt is paid off.
 	 */
-	if (!iocg->abs_vdebt && abs_cost)
+	if (!iocg->abs_vdebt && abs_cost) {
+		iocg->indebt_since = now->now;
 		propagate_weights(iocg, iocg->active, 0, false, now);
+	}
 
 	iocg->abs_vdebt += abs_cost;
 
@@ -1348,9 +1362,13 @@ static void iocg_pay_debt(struct ioc_gq *iocg, u64 abs_vpay,
 	iocg->abs_vdebt -= min(abs_vpay, iocg->abs_vdebt);
 
 	/* if debt is paid in full, restore inuse */
-	if (!iocg->abs_vdebt)
+	if (!iocg->abs_vdebt) {
+		iocg->local_stat.indebt_us += now->now - iocg->indebt_since;
+		iocg->indebt_since = 0;
+
 		propagate_weights(iocg, iocg->active, iocg->last_inuse,
 				  false, now);
+	}
 }
 
 static int iocg_wake_fn(struct wait_queue_entry *wq_entry, unsigned mode,
@@ -1436,8 +1454,17 @@ static void iocg_kick_waitq(struct ioc_gq *iocg, bool pay_debt,
 
 	__wake_up_locked_key(&iocg->waitq, TASK_NORMAL, &ctx);
 
-	if (!waitqueue_active(&iocg->waitq))
+	if (!waitqueue_active(&iocg->waitq)) {
+		if (iocg->wait_since) {
+			iocg->local_stat.wait_us += now->now - iocg->wait_since;
+			iocg->wait_since = 0;
+		}
 		return;
+	}
+
+	if (!iocg->wait_since)
+		iocg->wait_since = now->now;
+
 	if (WARN_ON_ONCE(ctx.vbudget >= 0))
 		return;
 
@@ -1579,8 +1606,15 @@ static void iocg_flush_stat_one(struct ioc_gq *iocg, struct ioc_now *now)
 	iocg->usage_delta_us = div64_u64(vusage_delta, ioc->vtime_base_rate);
 	iocg->local_stat.usage_us += iocg->usage_delta_us;
 
+	/* propagate upwards */
 	new_stat.usage_us =
 		iocg->local_stat.usage_us + iocg->desc_stat.usage_us;
+	new_stat.wait_us =
+		iocg->local_stat.wait_us + iocg->desc_stat.wait_us;
+	new_stat.indebt_us =
+		iocg->local_stat.indebt_us + iocg->desc_stat.indebt_us;
+	new_stat.indelay_us =
+		iocg->local_stat.indelay_us + iocg->desc_stat.indelay_us;
 
 	/* propagate the deltas to the parent */
 	if (iocg->level > 0) {
@@ -1589,6 +1623,12 @@ static void iocg_flush_stat_one(struct ioc_gq *iocg, struct ioc_now *now)
 
 		parent_stat->usage_us +=
 			new_stat.usage_us - iocg->last_stat.usage_us;
+		parent_stat->wait_us +=
+			new_stat.wait_us - iocg->last_stat.wait_us;
+		parent_stat->indebt_us +=
+			new_stat.indebt_us - iocg->last_stat.indebt_us;
+		parent_stat->indelay_us +=
+			new_stat.indelay_us - iocg->last_stat.indelay_us;
 	}
 
 	iocg->last_stat = new_stat;
@@ -1961,8 +2001,6 @@ static void ioc_timer_fn(struct timer_list *timer)
 		return;
 	}
 
-	iocg_flush_stat(&ioc->active_iocgs, &now);
-
 	/*
 	 * Waiters determine the sleep durations based on the vrate they
 	 * saw at the time of sleep.  If vrate has increased, some waiters
@@ -1976,6 +2014,22 @@ static void ioc_timer_fn(struct timer_list *timer)
 
 		spin_lock(&iocg->waitq.lock);
 
+		/* flush wait and indebt stat deltas */
+		if (iocg->wait_since) {
+			iocg->local_stat.wait_us += now.now - iocg->wait_since;
+			iocg->wait_since = now.now;
+		}
+		if (iocg->indebt_since) {
+			iocg->local_stat.indebt_us +=
+				now.now - iocg->indebt_since;
+			iocg->indebt_since = now.now;
+		}
+		if (iocg->indelay_since) {
+			iocg->local_stat.indelay_us +=
+				now.now - iocg->indelay_since;
+			iocg->indelay_since = now.now;
+		}
+
 		if (waitqueue_active(&iocg->waitq) || iocg->abs_vdebt ||
 		    iocg->delay) {
 			/* might be oversleeping vtime / hweight changes, kick */
@@ -2010,6 +2064,12 @@ static void ioc_timer_fn(struct timer_list *timer)
 	}
 	commit_weights(ioc);
 
+	/*
+	 * Wait and indebt stat are flushed above and the donation calculation
+	 * below needs updated usage stat. Let's bring stat up-to-date.
+	 */
+	iocg_flush_stat(&ioc->active_iocgs, &now);
+
 	/* calc usage and see whether some weights need to be moved around */
 	list_for_each_entry(iocg, &ioc->active_iocgs, active_list) {
 		u64 vdone, vtime, usage_us, usage_dur;
@@ -2835,6 +2895,13 @@ static size_t ioc_pd_stat(struct blkg_policy_data *pd, char *buf, size_t size)
 	pos += scnprintf(buf + pos, size - pos, " cost.usage=%llu",
 			 iocg->last_stat.usage_us);
 
+	if (blkcg_debug_stats)
+		pos += scnprintf(buf + pos, size - pos,
+				 " cost.wait=%llu cost.indebt=%llu cost.indelay=%llu",
+				 iocg->last_stat.wait_us,
+				 iocg->last_stat.indebt_us,
+				 iocg->last_stat.indelay_us);
+
 	return pos;
 }