blk-throttle: remove CONFIG_BLK_DEV_THROTTLING_LOW

One the one hand, it's marked EXPERIMENTAL since 2017, and looks like
there are no users since then, and no testers and no developers, it's
just not active at all.

On the other hand, even if the config is disabled, there are still many
fields in throtl_grp and throtl_data and many functions that are only
used for throtl low.

At last, currently blk-throtl is initialized during disk initialization,
and destroyed during disk removal, and it exposes many functions to be
called directly from block layer.

Remove throtl low to make code much more cleaner and follow up work much
easier.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20240509121107.3195568-2-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 38 insertions, 850 deletions

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index c515e1a96fad..d907040859f9 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -25,18 +25,6 @@
 #define DFL_THROTL_SLICE_HD (HZ / 10)
 #define DFL_THROTL_SLICE_SSD (HZ / 50)
 #define MAX_THROTL_SLICE (HZ)
-#define MAX_IDLE_TIME (5L * 1000 * 1000) /* 5 s */
-#define MIN_THROTL_BPS (320 * 1024)
-#define MIN_THROTL_IOPS (10)
-#define DFL_LATENCY_TARGET (-1L)
-#define DFL_IDLE_THRESHOLD (0)
-#define DFL_HD_BASELINE_LATENCY (4000L) /* 4ms */
-#define LATENCY_FILTERED_SSD (0)
-/*
- * For HD, very small latency comes from sequential IO. Such IO is helpless to
- * help determine if its IO is impacted by others, hence we ignore the IO
- */
-#define LATENCY_FILTERED_HD (1000L) /* 1ms */
 
 /* A workqueue to queue throttle related work */
 static struct workqueue_struct *kthrotld_workqueue;
@@ -70,19 +58,6 @@ struct throtl_data
 
 	/* Work for dispatching throttled bios */
 	struct work_struct dispatch_work;
-	unsigned int limit_index;
-	bool limit_valid[LIMIT_CNT];
-
-	unsigned long low_upgrade_time;
-	unsigned long low_downgrade_time;
-
-	unsigned int scale;
-
-	struct latency_bucket tmp_buckets[2][LATENCY_BUCKET_SIZE];
-	struct avg_latency_bucket avg_buckets[2][LATENCY_BUCKET_SIZE];
-	struct latency_bucket __percpu *latency_buckets[2];
-	unsigned long last_calculate_time;
-	unsigned long filtered_latency;
 
 	bool track_bio_latency;
 };
@@ -126,84 +101,24 @@ static struct throtl_data *sq_to_td(struct throtl_service_queue *sq)
 		return container_of(sq, struct throtl_data, service_queue);
 }
 
-/*
- * cgroup's limit in LIMIT_MAX is scaled if low limit is set. This scale is to
- * make the IO dispatch more smooth.
- * Scale up: linearly scale up according to elapsed time since upgrade. For
- *           every throtl_slice, the limit scales up 1/2 .low limit till the
- *           limit hits .max limit
- * Scale down: exponentially scale down if a cgroup doesn't hit its .low limit
- */
-static uint64_t throtl_adjusted_limit(uint64_t low, struct throtl_data *td)
-{
-	/* arbitrary value to avoid too big scale */
-	if (td->scale < 4096 && time_after_eq(jiffies,
-	    td->low_upgrade_time + td->scale * td->throtl_slice))
-		td->scale = (jiffies - td->low_upgrade_time) / td->throtl_slice;
-
-	return low + (low >> 1) * td->scale;
-}
-
 static uint64_t tg_bps_limit(struct throtl_grp *tg, int rw)
 {
 	struct blkcg_gq *blkg = tg_to_blkg(tg);
-	struct throtl_data *td;
-	uint64_t ret;
 
 	if (cgroup_subsys_on_dfl(io_cgrp_subsys) && !blkg->parent)
 		return U64_MAX;
 
-	td = tg->td;
-	ret = tg->bps[rw][td->limit_index];
-	if (ret == 0 && td->limit_index == LIMIT_LOW) {
-		/* intermediate node or iops isn't 0 */
-		if (!list_empty(&blkg->blkcg->css.children) ||
-		    tg->iops[rw][td->limit_index])
-			return U64_MAX;
-		else
-			return MIN_THROTL_BPS;
-	}
-
-	if (td->limit_index == LIMIT_MAX && tg->bps[rw][LIMIT_LOW] &&
-	    tg->bps[rw][LIMIT_LOW] != tg->bps[rw][LIMIT_MAX]) {
-		uint64_t adjusted;
-
-		adjusted = throtl_adjusted_limit(tg->bps[rw][LIMIT_LOW], td);
-		ret = min(tg->bps[rw][LIMIT_MAX], adjusted);
-	}
-	return ret;
+	return tg->bps[rw];
 }
 
 static unsigned int tg_iops_limit(struct throtl_grp *tg, int rw)
 {
 	struct blkcg_gq *blkg = tg_to_blkg(tg);
-	struct throtl_data *td;
-	unsigned int ret;
 
 	if (cgroup_subsys_on_dfl(io_cgrp_subsys) && !blkg->parent)
 		return UINT_MAX;
 
-	td = tg->td;
-	ret = tg->iops[rw][td->limit_index];
-	if (ret == 0 && tg->td->limit_index == LIMIT_LOW) {
-		/* intermediate node or bps isn't 0 */
-		if (!list_empty(&blkg->blkcg->css.children) ||
-		    tg->bps[rw][td->limit_index])
-			return UINT_MAX;
-		else
-			return MIN_THROTL_IOPS;
-	}
-
-	if (td->limit_index == LIMIT_MAX && tg->iops[rw][LIMIT_LOW] &&
-	    tg->iops[rw][LIMIT_LOW] != tg->iops[rw][LIMIT_MAX]) {
-		uint64_t adjusted;
-
-		adjusted = throtl_adjusted_limit(tg->iops[rw][LIMIT_LOW], td);
-		if (adjusted > UINT_MAX)
-			adjusted = UINT_MAX;
-		ret = min_t(unsigned int, tg->iops[rw][LIMIT_MAX], adjusted);
-	}
-	return ret;
+	return tg->iops[rw];
 }
 
 #define request_bucket_index(sectors) \
@@ -359,20 +274,10 @@ static struct blkg_policy_data *throtl_pd_alloc(struct gendisk *disk,
 	}
 
 	RB_CLEAR_NODE(&tg->rb_node);
-	tg->bps[READ][LIMIT_MAX] = U64_MAX;
-	tg->bps[WRITE][LIMIT_MAX] = U64_MAX;
-	tg->iops[READ][LIMIT_MAX] = UINT_MAX;
-	tg->iops[WRITE][LIMIT_MAX] = UINT_MAX;
-	tg->bps_conf[READ][LIMIT_MAX] = U64_MAX;
-	tg->bps_conf[WRITE][LIMIT_MAX] = U64_MAX;
-	tg->iops_conf[READ][LIMIT_MAX] = UINT_MAX;
-	tg->iops_conf[WRITE][LIMIT_MAX] = UINT_MAX;
-	/* LIMIT_LOW will have default value 0 */
-
-	tg->latency_target = DFL_LATENCY_TARGET;
-	tg->latency_target_conf = DFL_LATENCY_TARGET;
-	tg->idletime_threshold = DFL_IDLE_THRESHOLD;
-	tg->idletime_threshold_conf = DFL_IDLE_THRESHOLD;
+	tg->bps[READ] = U64_MAX;
+	tg->bps[WRITE] = U64_MAX;
+	tg->iops[READ] = UINT_MAX;
+	tg->iops[WRITE] = UINT_MAX;
 
 	return &tg->pd;
 
@@ -418,18 +323,15 @@ static void throtl_pd_init(struct blkg_policy_data *pd)
 static void tg_update_has_rules(struct throtl_grp *tg)
 {
 	struct throtl_grp *parent_tg = sq_to_tg(tg->service_queue.parent_sq);
-	struct throtl_data *td = tg->td;
 	int rw;
 
 	for (rw = READ; rw <= WRITE; rw++) {
 		tg->has_rules_iops[rw] =
 			(parent_tg && parent_tg->has_rules_iops[rw]) ||
-			(td->limit_valid[td->limit_index] &&
-			  tg_iops_limit(tg, rw) != UINT_MAX);
+			tg_iops_limit(tg, rw) != UINT_MAX;
 		tg->has_rules_bps[rw] =
 			(parent_tg && parent_tg->has_rules_bps[rw]) ||
-			(td->limit_valid[td->limit_index] &&
-			 (tg_bps_limit(tg, rw) != U64_MAX));
+			tg_bps_limit(tg, rw) != U64_MAX;
 	}
 }
 
@@ -443,49 +345,6 @@ static void throtl_pd_online(struct blkg_policy_data *pd)
 	tg_update_has_rules(tg);
 }
 
-#ifdef CONFIG_BLK_DEV_THROTTLING_LOW
-static void blk_throtl_update_limit_valid(struct throtl_data *td)
-{
-	struct cgroup_subsys_state *pos_css;
-	struct blkcg_gq *blkg;
-	bool low_valid = false;
-
-	rcu_read_lock();
-	blkg_for_each_descendant_post(blkg, pos_css, td->queue->root_blkg) {
-		struct throtl_grp *tg = blkg_to_tg(blkg);
-
-		if (tg->bps[READ][LIMIT_LOW] || tg->bps[WRITE][LIMIT_LOW] ||
-		    tg->iops[READ][LIMIT_LOW] || tg->iops[WRITE][LIMIT_LOW]) {
-			low_valid = true;
-			break;
-		}
-	}
-	rcu_read_unlock();
-
-	td->limit_valid[LIMIT_LOW] = low_valid;
-}
-#else
-static inline void blk_throtl_update_limit_valid(struct throtl_data *td)
-{
-}
-#endif
-
-static void throtl_upgrade_state(struct throtl_data *td);
-static void throtl_pd_offline(struct blkg_policy_data *pd)
-{
-	struct throtl_grp *tg = pd_to_tg(pd);
-
-	tg->bps[READ][LIMIT_LOW] = 0;
-	tg->bps[WRITE][LIMIT_LOW] = 0;
-	tg->iops[READ][LIMIT_LOW] = 0;
-	tg->iops[WRITE][LIMIT_LOW] = 0;
-
-	blk_throtl_update_limit_valid(tg->td);
-
-	if (!tg->td->limit_valid[tg->td->limit_index])
-		throtl_upgrade_state(tg->td);
-}
-
 static void throtl_pd_free(struct blkg_policy_data *pd)
 {
 	struct throtl_grp *tg = pd_to_tg(pd);
@@ -1151,8 +1010,6 @@ static int throtl_select_dispatch(struct throtl_service_queue *parent_sq)
 	return nr_disp;
 }
 
-static bool throtl_can_upgrade(struct throtl_data *td,
-	struct throtl_grp *this_tg);
 /**
  * throtl_pending_timer_fn - timer function for service_queue->pending_timer
  * @t: the pending_timer member of the throtl_service_queue being serviced
@@ -1189,9 +1046,6 @@ static void throtl_pending_timer_fn(struct timer_list *t)
 	if (!q->root_blkg)
 		goto out_unlock;
 
-	if (throtl_can_upgrade(td, NULL))
-		throtl_upgrade_state(td);
-
 again:
 	parent_sq = sq->parent_sq;
 	dispatched = false;
@@ -1331,22 +1185,12 @@ static void tg_conf_updated(struct throtl_grp *tg, bool global)
 	blkg_for_each_descendant_pre(blkg, pos_css,
 			global ? tg->td->queue->root_blkg : tg_to_blkg(tg)) {
 		struct throtl_grp *this_tg = blkg_to_tg(blkg);
-		struct throtl_grp *parent_tg;
 
 		tg_update_has_rules(this_tg);
 		/* ignore root/second level */
 		if (!cgroup_subsys_on_dfl(io_cgrp_subsys) || !blkg->parent ||
 		    !blkg->parent->parent)
 			continue;
-		parent_tg = blkg_to_tg(blkg->parent);
-		/*
-		 * make sure all children has lower idle time threshold and
-		 * higher latency target
-		 */
-		this_tg->idletime_threshold = min(this_tg->idletime_threshold,
-				parent_tg->idletime_threshold);
-		this_tg->latency_target = max(this_tg->latency_target,
-				parent_tg->latency_target);
 	}
 	rcu_read_unlock();
 
@@ -1444,25 +1288,25 @@ static int tg_print_rwstat_recursive(struct seq_file *sf, void *v)
 static struct cftype throtl_legacy_files[] = {
 	{
 		.name = "throttle.read_bps_device",
-		.private = offsetof(struct throtl_grp, bps[READ][LIMIT_MAX]),
+		.private = offsetof(struct throtl_grp, bps[READ]),
 		.seq_show = tg_print_conf_u64,
 		.write = tg_set_conf_u64,
 	},
 	{
 		.name = "throttle.write_bps_device",
-		.private = offsetof(struct throtl_grp, bps[WRITE][LIMIT_MAX]),
+		.private = offsetof(struct throtl_grp, bps[WRITE]),
 		.seq_show = tg_print_conf_u64,
 		.write = tg_set_conf_u64,
 	},
 	{
 		.name = "throttle.read_iops_device",
-		.private = offsetof(struct throtl_grp, iops[READ][LIMIT_MAX]),
+		.private = offsetof(struct throtl_grp, iops[READ]),
 		.seq_show = tg_print_conf_uint,
 		.write = tg_set_conf_uint,
 	},
 	{
 		.name = "throttle.write_iops_device",
-		.private = offsetof(struct throtl_grp, iops[WRITE][LIMIT_MAX]),
+		.private = offsetof(struct throtl_grp, iops[WRITE]),
 		.seq_show = tg_print_conf_uint,
 		.write = tg_set_conf_uint,
 	},
@@ -1500,55 +1344,36 @@ static u64 tg_prfill_limit(struct seq_file *sf, struct blkg_policy_data *pd,
 	if (!dname)
 		return 0;
 
-	if (off == LIMIT_LOW) {
-		bps_dft = 0;
-		iops_dft = 0;
-	} else {
-		bps_dft = U64_MAX;
-		iops_dft = UINT_MAX;
-	}
+	bps_dft = U64_MAX;
+	iops_dft = UINT_MAX;
 
-	if (tg->bps_conf[READ][off] == bps_dft &&
-	    tg->bps_conf[WRITE][off] == bps_dft &&
-	    tg->iops_conf[READ][off] == iops_dft &&
-	    tg->iops_conf[WRITE][off] == iops_dft &&
-	    (off != LIMIT_LOW ||
-	     (tg->idletime_threshold_conf == DFL_IDLE_THRESHOLD &&
-	      tg->latency_target_conf == DFL_LATENCY_TARGET)))
+	if (tg->bps_conf[READ] == bps_dft &&
+	    tg->bps_conf[WRITE] == bps_dft &&
+	    tg->iops_conf[READ] == iops_dft &&
+	    tg->iops_conf[WRITE] == iops_dft)
 		return 0;
 
 	seq_printf(sf, "%s", dname);
-	if (tg->bps_conf[READ][off] == U64_MAX)
+	if (tg->bps_conf[READ] == U64_MAX)
 		seq_printf(sf, " rbps=max");
 	else
-		seq_printf(sf, " rbps=%llu", tg->bps_conf[READ][off]);
+		seq_printf(sf, " rbps=%llu", tg->bps_conf[READ]);
 
-	if (tg->bps_conf[WRITE][off] == U64_MAX)
+	if (tg->bps_conf[WRITE] == U64_MAX)
 		seq_printf(sf, " wbps=max");
 	else
-		seq_printf(sf, " wbps=%llu", tg->bps_conf[WRITE][off]);
+		seq_printf(sf, " wbps=%llu", tg->bps_conf[WRITE]);
 
-	if (tg->iops_conf[READ][off] == UINT_MAX)
+	if (tg->iops_conf[READ] == UINT_MAX)
 		seq_printf(sf, " riops=max");
 	else
-		seq_printf(sf, " riops=%u", tg->iops_conf[READ][off]);
+		seq_printf(sf, " riops=%u", tg->iops_conf[READ]);
 
-	if (tg->iops_conf[WRITE][off] == UINT_MAX)
+	if (tg->iops_conf[WRITE] == UINT_MAX)
 		seq_printf(sf, " wiops=max");
 	else
-		seq_printf(sf, " wiops=%u", tg->iops_conf[WRITE][off]);
+		seq_printf(sf, " wiops=%u", tg->iops_conf[WRITE]);
 
-	if (off == LIMIT_LOW) {
-		if (tg->idletime_threshold_conf == ULONG_MAX)
-			seq_printf(sf, " idle=max");
-		else
-			seq_printf(sf, " idle=%lu", tg->idletime_threshold_conf);
-
-		if (tg->latency_target_conf == ULONG_MAX)
-			seq_printf(sf, " latency=max");
-		else
-			seq_printf(sf, " latency=%lu", tg->latency_target_conf);
-	}
 	seq_printf(sf, "\n");
 	return 0;
 }
@@ -1567,10 +1392,7 @@ static ssize_t tg_set_limit(struct kernfs_open_file *of,
 	struct blkg_conf_ctx ctx;
 	struct throtl_grp *tg;
 	u64 v[4];
-	unsigned long idle_time;
-	unsigned long latency_time;
 	int ret;
-	int index = of_cft(of)->private;
 
 	blkg_conf_init(&ctx, buf);
 
@@ -1581,13 +1403,11 @@ static ssize_t tg_set_limit(struct kernfs_open_file *of,
 	tg = blkg_to_tg(ctx.blkg);
 	tg_update_carryover(tg);
 
-	v[0] = tg->bps_conf[READ][index];
-	v[1] = tg->bps_conf[WRITE][index];
-	v[2] = tg->iops_conf[READ][index];
-	v[3] = tg->iops_conf[WRITE][index];
+	v[0] = tg->bps[READ];
+	v[1] = tg->bps[WRITE];
+	v[2] = tg->iops[READ];
+	v[3] = tg->iops[WRITE];
 
-	idle_time = tg->idletime_threshold_conf;
-	latency_time = tg->latency_target_conf;
 	while (true) {
 		char tok[27];	/* wiops=18446744073709551616 */
 		char *p;
@@ -1619,60 +1439,16 @@ static ssize_t tg_set_limit(struct kernfs_open_file *of,
 			v[2] = min_t(u64, val, UINT_MAX);
 		else if (!strcmp(tok, "wiops") && val > 1)
 			v[3] = min_t(u64, val, UINT_MAX);
-		else if (off == LIMIT_LOW && !strcmp(tok, "idle"))
-			idle_time = val;
-		else if (off == LIMIT_LOW && !strcmp(tok, "latency"))
-			latency_time = val;
 		else
 			goto out_finish;
 	}
 
-	tg->bps_conf[READ][index] = v[0];
-	tg->bps_conf[WRITE][index] = v[1];
-	tg->iops_conf[READ][index] = v[2];
-	tg->iops_conf[WRITE][index] = v[3];
+	tg->bps[READ] = v[0];
+	tg->bps[WRITE] = v[1];
+	tg->iops[READ] = v[2];
+	tg->iops[WRITE] = v[3];
 
-	if (index == LIMIT_MAX) {
-		tg->bps[READ][index] = v[0];
-		tg->bps[WRITE][index] = v[1];
-		tg->iops[READ][index] = v[2];
-		tg->iops[WRITE][index] = v[3];
-	}
-	tg->bps[READ][LIMIT_LOW] = min(tg->bps_conf[READ][LIMIT_LOW],
-		tg->bps_conf[READ][LIMIT_MAX]);
-	tg->bps[WRITE][LIMIT_LOW] = min(tg->bps_conf[WRITE][LIMIT_LOW],
-		tg->bps_conf[WRITE][LIMIT_MAX]);
-	tg->iops[READ][LIMIT_LOW] = min(tg->iops_conf[READ][LIMIT_LOW],
-		tg->iops_conf[READ][LIMIT_MAX]);
-	tg->iops[WRITE][LIMIT_LOW] = min(tg->iops_conf[WRITE][LIMIT_LOW],
-		tg->iops_conf[WRITE][LIMIT_MAX]);
-	tg->idletime_threshold_conf = idle_time;
-	tg->latency_target_conf = latency_time;
-
-	/* force user to configure all settings for low limit  */
-	if (!(tg->bps[READ][LIMIT_LOW] || tg->iops[READ][LIMIT_LOW] ||
-	      tg->bps[WRITE][LIMIT_LOW] || tg->iops[WRITE][LIMIT_LOW]) ||
-	    tg->idletime_threshold_conf == DFL_IDLE_THRESHOLD ||
-	    tg->latency_target_conf == DFL_LATENCY_TARGET) {
-		tg->bps[READ][LIMIT_LOW] = 0;
-		tg->bps[WRITE][LIMIT_LOW] = 0;
-		tg->iops[READ][LIMIT_LOW] = 0;
-		tg->iops[WRITE][LIMIT_LOW] = 0;
-		tg->idletime_threshold = DFL_IDLE_THRESHOLD;
-		tg->latency_target = DFL_LATENCY_TARGET;
-	} else if (index == LIMIT_LOW) {
-		tg->idletime_threshold = tg->idletime_threshold_conf;
-		tg->latency_target = tg->latency_target_conf;
-	}
-
-	blk_throtl_update_limit_valid(tg->td);
-	if (tg->td->limit_valid[LIMIT_LOW]) {
-		if (index == LIMIT_LOW)
-			tg->td->limit_index = LIMIT_LOW;
-	} else
-		tg->td->limit_index = LIMIT_MAX;
-	tg_conf_updated(tg, index == LIMIT_LOW &&
-		tg->td->limit_valid[LIMIT_LOW]);
+	tg_conf_updated(tg, false);
 	ret = 0;
 out_finish:
 	blkg_conf_exit(&ctx);
@@ -1680,21 +1456,11 @@ out_finish:
 }
 
 static struct cftype throtl_files[] = {
-#ifdef CONFIG_BLK_DEV_THROTTLING_LOW
-	{
-		.name = "low",
-		.flags = CFTYPE_NOT_ON_ROOT,
-		.seq_show = tg_print_limit,
-		.write = tg_set_limit,
-		.private = LIMIT_LOW,
-	},
-#endif
 	{
 		.name = "max",
 		.flags = CFTYPE_NOT_ON_ROOT,
 		.seq_show = tg_print_limit,
 		.write = tg_set_limit,
-		.private = LIMIT_MAX,
 	},
 	{ }	/* terminate */
 };
@@ -1713,7 +1479,6 @@ struct blkcg_policy blkcg_policy_throtl = {
 	.pd_alloc_fn		= throtl_pd_alloc,
 	.pd_init_fn		= throtl_pd_init,
 	.pd_online_fn		= throtl_pd_online,
-	.pd_offline_fn		= throtl_pd_offline,
 	.pd_free_fn		= throtl_pd_free,
 };
 
@@ -1762,418 +1527,6 @@ void blk_throtl_cancel_bios(struct gendisk *disk)
 	spin_unlock_irq(&q->queue_lock);
 }
 
-#ifdef CONFIG_BLK_DEV_THROTTLING_LOW
-static unsigned long __tg_last_low_overflow_time(struct throtl_grp *tg)
-{
-	unsigned long rtime = jiffies, wtime = jiffies;
-
-	if (tg->bps[READ][LIMIT_LOW] || tg->iops[READ][LIMIT_LOW])
-		rtime = tg->last_low_overflow_time[READ];
-	if (tg->bps[WRITE][LIMIT_LOW] || tg->iops[WRITE][LIMIT_LOW])
-		wtime = tg->last_low_overflow_time[WRITE];
-	return min(rtime, wtime);
-}
-
-static unsigned long tg_last_low_overflow_time(struct throtl_grp *tg)
-{
-	struct throtl_service_queue *parent_sq;
-	struct throtl_grp *parent = tg;
-	unsigned long ret = __tg_last_low_overflow_time(tg);
-
-	while (true) {
-		parent_sq = parent->service_queue.parent_sq;
-		parent = sq_to_tg(parent_sq);
-		if (!parent)
-			break;
-
-		/*
-		 * The parent doesn't have low limit, it always reaches low
-		 * limit. Its overflow time is useless for children
-		 */
-		if (!parent->bps[READ][LIMIT_LOW] &&
-		    !parent->iops[READ][LIMIT_LOW] &&
-		    !parent->bps[WRITE][LIMIT_LOW] &&
-		    !parent->iops[WRITE][LIMIT_LOW])
-			continue;
-		if (time_after(__tg_last_low_overflow_time(parent), ret))
-			ret = __tg_last_low_overflow_time(parent);
-	}
-	return ret;
-}
-
-static bool throtl_tg_is_idle(struct throtl_grp *tg)
-{
-	/*
-	 * cgroup is idle if:
-	 * - single idle is too long, longer than a fixed value (in case user
-	 *   configure a too big threshold) or 4 times of idletime threshold
-	 * - average think time is more than threshold
-	 * - IO latency is largely below threshold
-	 */
-	unsigned long time;
-	bool ret;
-
-	time = min_t(unsigned long, MAX_IDLE_TIME, 4 * tg->idletime_threshold);
-	ret = tg->latency_target == DFL_LATENCY_TARGET ||
-	      tg->idletime_threshold == DFL_IDLE_THRESHOLD ||
-	      (blk_time_get_ns() >> 10) - tg->last_finish_time > time ||
-	      tg->avg_idletime > tg->idletime_threshold ||
-	      (tg->latency_target && tg->bio_cnt &&
-		tg->bad_bio_cnt * 5 < tg->bio_cnt);
-	throtl_log(&tg->service_queue,
-		"avg_idle=%ld, idle_threshold=%ld, bad_bio=%d, total_bio=%d, is_idle=%d, scale=%d",
-		tg->avg_idletime, tg->idletime_threshold, tg->bad_bio_cnt,
-		tg->bio_cnt, ret, tg->td->scale);
-	return ret;
-}
-
-static bool throtl_low_limit_reached(struct throtl_grp *tg, int rw)
-{
-	struct throtl_service_queue *sq = &tg->service_queue;
-	bool limit = tg->bps[rw][LIMIT_LOW] || tg->iops[rw][LIMIT_LOW];
-
-	/*
-	 * if low limit is zero, low limit is always reached.
-	 * if low limit is non-zero, we can check if there is any request
-	 * is queued to determine if low limit is reached as we throttle
-	 * request according to limit.
-	 */
-	return !limit || sq->nr_queued[rw];
-}
-
-static bool throtl_tg_can_upgrade(struct throtl_grp *tg)
-{
-	/*
-	 * cgroup reaches low limit when low limit of READ and WRITE are
-	 * both reached, it's ok to upgrade to next limit if cgroup reaches
-	 * low limit
-	 */
-	if (throtl_low_limit_reached(tg, READ) &&
-	    throtl_low_limit_reached(tg, WRITE))
-		return true;
-
-	if (time_after_eq(jiffies,
-		tg_last_low_overflow_time(tg) + tg->td->throtl_slice) &&
-	    throtl_tg_is_idle(tg))
-		return true;
-	return false;
-}
-
-static bool throtl_hierarchy_can_upgrade(struct throtl_grp *tg)
-{
-	while (true) {
-		if (throtl_tg_can_upgrade(tg))
-			return true;
-		tg = sq_to_tg(tg->service_queue.parent_sq);
-		if (!tg || !tg_to_blkg(tg)->parent)
-			return false;
-	}
-	return false;
-}
-
-static bool throtl_can_upgrade(struct throtl_data *td,
-	struct throtl_grp *this_tg)
-{
-	struct cgroup_subsys_state *pos_css;
-	struct blkcg_gq *blkg;
-
-	if (td->limit_index != LIMIT_LOW)
-		return false;
-
-	if (time_before(jiffies, td->low_downgrade_time + td->throtl_slice))
-		return false;
-
-	rcu_read_lock();
-	blkg_for_each_descendant_post(blkg, pos_css, td->queue->root_blkg) {
-		struct throtl_grp *tg = blkg_to_tg(blkg);
-
-		if (tg == this_tg)
-			continue;
-		if (!list_empty(&tg_to_blkg(tg)->blkcg->css.children))
-			continue;
-		if (!throtl_hierarchy_can_upgrade(tg)) {
-			rcu_read_unlock();
-			return false;
-		}
-	}
-	rcu_read_unlock();
-	return true;
-}
-
-static void throtl_upgrade_check(struct throtl_grp *tg)
-{
-	unsigned long now = jiffies;
-
-	if (tg->td->limit_index != LIMIT_LOW)
-		return;
-
-	if (time_after(tg->last_check_time + tg->td->throtl_slice, now))
-		return;
-
-	tg->last_check_time = now;
-
-	if (!time_after_eq(now,
-	     __tg_last_low_overflow_time(tg) + tg->td->throtl_slice))
-		return;
-
-	if (throtl_can_upgrade(tg->td, NULL))
-		throtl_upgrade_state(tg->td);
-}
-
-static void throtl_upgrade_state(struct throtl_data *td)
-{
-	struct cgroup_subsys_state *pos_css;
-	struct blkcg_gq *blkg;
-
-	throtl_log(&td->service_queue, "upgrade to max");
-	td->limit_index = LIMIT_MAX;
-	td->low_upgrade_time = jiffies;
-	td->scale = 0;
-	rcu_read_lock();
-	blkg_for_each_descendant_post(blkg, pos_css, td->queue->root_blkg) {
-		struct throtl_grp *tg = blkg_to_tg(blkg);
-		struct throtl_service_queue *sq = &tg->service_queue;
-
-		tg->disptime = jiffies - 1;
-		throtl_select_dispatch(sq);
-		throtl_schedule_next_dispatch(sq, true);
-	}
-	rcu_read_unlock();
-	throtl_select_dispatch(&td->service_queue);
-	throtl_schedule_next_dispatch(&td->service_queue, true);
-	queue_work(kthrotld_workqueue, &td->dispatch_work);
-}
-
-static void throtl_downgrade_state(struct throtl_data *td)
-{
-	td->scale /= 2;
-
-	throtl_log(&td->service_queue, "downgrade, scale %d", td->scale);
-	if (td->scale) {
-		td->low_upgrade_time = jiffies - td->scale * td->throtl_slice;
-		return;
-	}
-
-	td->limit_index = LIMIT_LOW;
-	td->low_downgrade_time = jiffies;
-}
-
-static bool throtl_tg_can_downgrade(struct throtl_grp *tg)
-{
-	struct throtl_data *td = tg->td;
-	unsigned long now = jiffies;
-
-	/*
-	 * If cgroup is below low limit, consider downgrade and throttle other
-	 * cgroups
-	 */
-	if (time_after_eq(now, tg_last_low_overflow_time(tg) +
-					td->throtl_slice) &&
-	    (!throtl_tg_is_idle(tg) ||
-	     !list_empty(&tg_to_blkg(tg)->blkcg->css.children)))
-		return true;
-	return false;
-}
-
-static bool throtl_hierarchy_can_downgrade(struct throtl_grp *tg)
-{
-	struct throtl_data *td = tg->td;
-
-	if (time_before(jiffies, td->low_upgrade_time + td->throtl_slice))
-		return false;
-
-	while (true) {
-		if (!throtl_tg_can_downgrade(tg))
-			return false;
-		tg = sq_to_tg(tg->service_queue.parent_sq);
-		if (!tg || !tg_to_blkg(tg)->parent)
-			break;
-	}
-	return true;
-}
-
-static void throtl_downgrade_check(struct throtl_grp *tg)
-{
-	uint64_t bps;
-	unsigned int iops;
-	unsigned long elapsed_time;
-	unsigned long now = jiffies;
-
-	if (tg->td->limit_index != LIMIT_MAX ||
-	    !tg->td->limit_valid[LIMIT_LOW])
-		return;
-	if (!list_empty(&tg_to_blkg(tg)->blkcg->css.children))
-		return;
-	if (time_after(tg->last_check_time + tg->td->throtl_slice, now))
-		return;
-
-	elapsed_time = now - tg->last_check_time;
-	tg->last_check_time = now;
-
-	if (time_before(now, tg_last_low_overflow_time(tg) +
-			tg->td->throtl_slice))
-		return;
-
-	if (tg->bps[READ][LIMIT_LOW]) {
-		bps = tg->last_bytes_disp[READ] * HZ;
-		do_div(bps, elapsed_time);
-		if (bps >= tg->bps[READ][LIMIT_LOW])
-			tg->last_low_overflow_time[READ] = now;
-	}
-
-	if (tg->bps[WRITE][LIMIT_LOW]) {
-		bps = tg->last_bytes_disp[WRITE] * HZ;
-		do_div(bps, elapsed_time);
-		if (bps >= tg->bps[WRITE][LIMIT_LOW])
-			tg->last_low_overflow_time[WRITE] = now;
-	}
-
-	if (tg->iops[READ][LIMIT_LOW]) {
-		iops = tg->last_io_disp[READ] * HZ / elapsed_time;
-		if (iops >= tg->iops[READ][LIMIT_LOW])
-			tg->last_low_overflow_time[READ] = now;
-	}
-
-	if (tg->iops[WRITE][LIMIT_LOW]) {
-		iops = tg->last_io_disp[WRITE] * HZ / elapsed_time;
-		if (iops >= tg->iops[WRITE][LIMIT_LOW])
-			tg->last_low_overflow_time[WRITE] = now;
-	}
-
-	/*
-	 * If cgroup is below low limit, consider downgrade and throttle other
-	 * cgroups
-	 */
-	if (throtl_hierarchy_can_downgrade(tg))
-		throtl_downgrade_state(tg->td);
-
-	tg->last_bytes_disp[READ] = 0;
-	tg->last_bytes_disp[WRITE] = 0;
-	tg->last_io_disp[READ] = 0;
-	tg->last_io_disp[WRITE] = 0;
-}
-
-static void blk_throtl_update_idletime(struct throtl_grp *tg)
-{
-	unsigned long now;
-	unsigned long last_finish_time = tg->last_finish_time;
-
-	if (last_finish_time == 0)
-		return;
-
-	now = blk_time_get_ns() >> 10;
-	if (now <= last_finish_time ||
-	    last_finish_time == tg->checked_last_finish_time)
-		return;
-
-	tg->avg_idletime = (tg->avg_idletime * 7 + now - last_finish_time) >> 3;
-	tg->checked_last_finish_time = last_finish_time;
-}
-
-static void throtl_update_latency_buckets(struct throtl_data *td)
-{
-	struct avg_latency_bucket avg_latency[2][LATENCY_BUCKET_SIZE];
-	int i, cpu, rw;
-	unsigned long last_latency[2] = { 0 };
-	unsigned long latency[2];
-
-	if (!blk_queue_nonrot(td->queue) || !td->limit_valid[LIMIT_LOW])
-		return;
-	if (time_before(jiffies, td->last_calculate_time + HZ))
-		return;
-	td->last_calculate_time = jiffies;
-
-	memset(avg_latency, 0, sizeof(avg_latency));
-	for (rw = READ; rw <= WRITE; rw++) {
-		for (i = 0; i < LATENCY_BUCKET_SIZE; i++) {
-			struct latency_bucket *tmp = &td->tmp_buckets[rw][i];
-
-			for_each_possible_cpu(cpu) {
-				struct latency_bucket *bucket;
-
-				/* this isn't race free, but ok in practice */
-				bucket = per_cpu_ptr(td->latency_buckets[rw],
-					cpu);
-				tmp->total_latency += bucket[i].total_latency;
-				tmp->samples += bucket[i].samples;
-				bucket[i].total_latency = 0;
-				bucket[i].samples = 0;
-			}
-
-			if (tmp->samples >= 32) {
-				int samples = tmp->samples;
-
-				latency[rw] = tmp->total_latency;
-
-				tmp->total_latency = 0;
-				tmp->samples = 0;
-				latency[rw] /= samples;
-				if (latency[rw] == 0)
-					continue;
-				avg_latency[rw][i].latency = latency[rw];
-			}
-		}
-	}
-
-	for (rw = READ; rw <= WRITE; rw++) {
-		for (i = 0; i < LATENCY_BUCKET_SIZE; i++) {
-			if (!avg_latency[rw][i].latency) {
-				if (td->avg_buckets[rw][i].latency < last_latency[rw])
-					td->avg_buckets[rw][i].latency =
-						last_latency[rw];
-				continue;
-			}
-
-			if (!td->avg_buckets[rw][i].valid)
-				latency[rw] = avg_latency[rw][i].latency;
-			else
-				latency[rw] = (td->avg_buckets[rw][i].latency * 7 +
-					avg_latency[rw][i].latency) >> 3;
-
-			td->avg_buckets[rw][i].latency = max(latency[rw],
-				last_latency[rw]);
-			td->avg_buckets[rw][i].valid = true;
-			last_latency[rw] = td->avg_buckets[rw][i].latency;
-		}
-	}
-
-	for (i = 0; i < LATENCY_BUCKET_SIZE; i++)
-		throtl_log(&td->service_queue,
-			"Latency bucket %d: read latency=%ld, read valid=%d, "
-			"write latency=%ld, write valid=%d", i,
-			td->avg_buckets[READ][i].latency,
-			td->avg_buckets[READ][i].valid,
-			td->avg_buckets[WRITE][i].latency,
-			td->avg_buckets[WRITE][i].valid);
-}
-#else
-static inline void throtl_update_latency_buckets(struct throtl_data *td)
-{
-}
-
-static void blk_throtl_update_idletime(struct throtl_grp *tg)
-{
-}
-
-static void throtl_downgrade_check(struct throtl_grp *tg)
-{
-}
-
-static void throtl_upgrade_check(struct throtl_grp *tg)
-{
-}
-
-static bool throtl_can_upgrade(struct throtl_data *td,
-	struct throtl_grp *this_tg)
-{
-	return false;
-}
-
-static void throtl_upgrade_state(struct throtl_data *td)
-{
-}
-#endif
-
 bool __blk_throtl_bio(struct bio *bio)
 {
 	struct request_queue *q = bdev_get_queue(bio->bi_bdev);
@@ -2186,21 +1539,12 @@ bool __blk_throtl_bio(struct bio *bio)
 	struct throtl_data *td = tg->td;
 
 	rcu_read_lock();
-
 	spin_lock_irq(&q->queue_lock);
-
-	throtl_update_latency_buckets(td);
-
-	blk_throtl_update_idletime(tg);
-
 	sq = &tg->service_queue;
 
-again:
 	while (true) {
 		if (tg->last_low_overflow_time[rw] == 0)
 			tg->last_low_overflow_time[rw] = jiffies;
-		throtl_downgrade_check(tg);
-		throtl_upgrade_check(tg);
 		/* throtl is FIFO - if bios are already queued, should queue */
 		if (sq->nr_queued[rw])
 			break;
@@ -2208,10 +1552,6 @@ again:
 		/* if above limits, break to queue */
 		if (!tg_may_dispatch(tg, bio, NULL)) {
 			tg->last_low_overflow_time[rw] = jiffies;
-			if (throtl_can_upgrade(td, tg)) {
-				throtl_upgrade_state(td);
-				goto again;
-			}
 			break;
 		}
 
@@ -2271,101 +1611,12 @@ again:
 	}
 
 out_unlock:
-#ifdef CONFIG_BLK_DEV_THROTTLING_LOW
-	if (throttled || !td->track_bio_latency)
-		bio->bi_issue.value |= BIO_ISSUE_THROTL_SKIP_LATENCY;
-#endif
 	spin_unlock_irq(&q->queue_lock);
 
 	rcu_read_unlock();
 	return throttled;
 }
 
-#ifdef CONFIG_BLK_DEV_THROTTLING_LOW
-static void throtl_track_latency(struct throtl_data *td, sector_t size,
-				 enum req_op op, unsigned long time)
-{
-	const bool rw = op_is_write(op);
-	struct latency_bucket *latency;
-	int index;
-
-	if (!td || td->limit_index != LIMIT_LOW ||
-	    !(op == REQ_OP_READ || op == REQ_OP_WRITE) ||
-	    !blk_queue_nonrot(td->queue))
-		return;
-
-	index = request_bucket_index(size);
-
-	latency = get_cpu_ptr(td->latency_buckets[rw]);
-	latency[index].total_latency += time;
-	latency[index].samples++;
-	put_cpu_ptr(td->latency_buckets[rw]);
-}
-
-void blk_throtl_stat_add(struct request *rq, u64 time_ns)
-{
-	struct request_queue *q = rq->q;
-	struct throtl_data *td = q->td;
-
-	throtl_track_latency(td, blk_rq_stats_sectors(rq), req_op(rq),
-			     time_ns >> 10);
-}
-
-void blk_throtl_bio_endio(struct bio *bio)
-{
-	struct blkcg_gq *blkg;
-	struct throtl_grp *tg;
-	u64 finish_time_ns;
-	unsigned long finish_time;
-	unsigned long start_time;
-	unsigned long lat;
-	int rw = bio_data_dir(bio);
-
-	blkg = bio->bi_blkg;
-	if (!blkg)
-		return;
-	tg = blkg_to_tg(blkg);
-	if (!tg->td->limit_valid[LIMIT_LOW])
-		return;
-
-	finish_time_ns = blk_time_get_ns();
-	tg->last_finish_time = finish_time_ns >> 10;
-
-	start_time = bio_issue_time(&bio->bi_issue) >> 10;
-	finish_time = __bio_issue_time(finish_time_ns) >> 10;
-	if (!start_time || finish_time <= start_time)
-		return;
-
-	lat = finish_time - start_time;
-	/* this is only for bio based driver */
-	if (!(bio->bi_issue.value & BIO_ISSUE_THROTL_SKIP_LATENCY))
-		throtl_track_latency(tg->td, bio_issue_size(&bio->bi_issue),
-				     bio_op(bio), lat);
-
-	if (tg->latency_target && lat >= tg->td->filtered_latency) {
-		int bucket;
-		unsigned int threshold;
-
-		bucket = request_bucket_index(bio_issue_size(&bio->bi_issue));
-		threshold = tg->td->avg_buckets[rw][bucket].latency +
-			tg->latency_target;
-		if (lat > threshold)
-			tg->bad_bio_cnt++;
-		/*
-		 * Not race free, could get wrong count, which means cgroups
-		 * will be throttled
-		 */
-		tg->bio_cnt++;
-	}
-
-	if (time_after(jiffies, tg->bio_cnt_reset_time) || tg->bio_cnt > 1024) {
-		tg->bio_cnt_reset_time = tg->td->throtl_slice + jiffies;
-		tg->bio_cnt /= 2;
-		tg->bad_bio_cnt /= 2;
-	}
-}
-#endif
-
 int blk_throtl_init(struct gendisk *disk)
 {
 	struct request_queue *q = disk->queue;
@@ -2375,19 +1626,6 @@ int blk_throtl_init(struct gendisk *disk)
 	td = kzalloc_node(sizeof(*td), GFP_KERNEL, q->node);
 	if (!td)
 		return -ENOMEM;
-	td->latency_buckets[READ] = __alloc_percpu(sizeof(struct latency_bucket) *
-		LATENCY_BUCKET_SIZE, __alignof__(u64));
-	if (!td->latency_buckets[READ]) {
-		kfree(td);
-		return -ENOMEM;
-	}
-	td->latency_buckets[WRITE] = __alloc_percpu(sizeof(struct latency_bucket) *
-		LATENCY_BUCKET_SIZE, __alignof__(u64));
-	if (!td->latency_buckets[WRITE]) {
-		free_percpu(td->latency_buckets[READ]);
-		kfree(td);
-		return -ENOMEM;
-	}
 
 	INIT_WORK(&td->dispatch_work, blk_throtl_dispatch_work_fn);
 	throtl_service_queue_init(&td->service_queue);
@@ -2395,18 +1633,10 @@ int blk_throtl_init(struct gendisk *disk)
 	q->td = td;
 	td->queue = q;
 
-	td->limit_valid[LIMIT_MAX] = true;
-	td->limit_index = LIMIT_MAX;
-	td->low_upgrade_time = jiffies;
-	td->low_downgrade_time = jiffies;
-
 	/* activate policy */
 	ret = blkcg_activate_policy(disk, &blkcg_policy_throtl);
-	if (ret) {
-		free_percpu(td->latency_buckets[READ]);
-		free_percpu(td->latency_buckets[WRITE]);
+	if (ret)
 		kfree(td);
-	}
 	return ret;
 }
 
@@ -2418,8 +1648,6 @@ void blk_throtl_exit(struct gendisk *disk)
 	del_timer_sync(&q->td->service_queue.pending_timer);
 	throtl_shutdown_wq(q);
 	blkcg_deactivate_policy(disk, &blkcg_policy_throtl);
-	free_percpu(q->td->latency_buckets[READ]);
-	free_percpu(q->td->latency_buckets[WRITE]);
 	kfree(q->td);
 }
 
@@ -2427,58 +1655,18 @@ void blk_throtl_register(struct gendisk *disk)
 {
 	struct request_queue *q = disk->queue;
 	struct throtl_data *td;
-	int i;
 
 	td = q->td;
 	BUG_ON(!td);
 
-	if (blk_queue_nonrot(q)) {
+	if (blk_queue_nonrot(q))
 		td->throtl_slice = DFL_THROTL_SLICE_SSD;
-		td->filtered_latency = LATENCY_FILTERED_SSD;
-	} else {
+	else
 		td->throtl_slice = DFL_THROTL_SLICE_HD;
-		td->filtered_latency = LATENCY_FILTERED_HD;
-		for (i = 0; i < LATENCY_BUCKET_SIZE; i++) {
-			td->avg_buckets[READ][i].latency = DFL_HD_BASELINE_LATENCY;
-			td->avg_buckets[WRITE][i].latency = DFL_HD_BASELINE_LATENCY;
-		}
-	}
-#ifndef CONFIG_BLK_DEV_THROTTLING_LOW
-	/* if no low limit, use previous default */
-	td->throtl_slice = DFL_THROTL_SLICE_HD;
-
-#else
 	td->track_bio_latency = !queue_is_mq(q);
 	if (!td->track_bio_latency)
 		blk_stat_enable_accounting(q);
-#endif
-}
-
-#ifdef CONFIG_BLK_DEV_THROTTLING_LOW
-ssize_t blk_throtl_sample_time_show(struct request_queue *q, char *page)
-{
-	if (!q->td)
-		return -EINVAL;
-	return sprintf(page, "%u\n", jiffies_to_msecs(q->td->throtl_slice));
-}
-
-ssize_t blk_throtl_sample_time_store(struct request_queue *q,
-	const char *page, size_t count)
-{
-	unsigned long v;
-	unsigned long t;
-
-	if (!q->td)
-		return -EINVAL;
-	if (kstrtoul(page, 10, &v))
-		return -EINVAL;
-	t = msecs_to_jiffies(v);
-	if (t == 0 || t > MAX_THROTL_SLICE)
-		return -EINVAL;
-	q->td->throtl_slice = t;
-	return count;
 }
-#endif
 
 static int __init throtl_init(void)
 {