Adding upstream version 5.10.209.upstream/5.10.209upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1051 insertions, 0 deletions

diff --git a/block/kyber-iosched.c b/block/kyber-iosched.c
new file mode 100644
index 000000000..7f9ef773b
--- /dev/null
+++ b/block/kyber-iosched.c
@@ -0,0 +1,1051 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * The Kyber I/O scheduler. Controls latency by throttling queue depths using
+ * scalable techniques.
+ *
+ * Copyright (C) 2017 Facebook
+ */
+
+#include <linux/kernel.h>
+#include <linux/blkdev.h>
+#include <linux/blk-mq.h>
+#include <linux/elevator.h>
+#include <linux/module.h>
+#include <linux/sbitmap.h>
+
+#include "blk.h"
+#include "blk-mq.h"
+#include "blk-mq-debugfs.h"
+#include "blk-mq-sched.h"
+#include "blk-mq-tag.h"
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/kyber.h>
+
+/*
+ * Scheduling domains: the device is divided into multiple domains based on the
+ * request type.
+ */
+enum {
+	KYBER_READ,
+	KYBER_WRITE,
+	KYBER_DISCARD,
+	KYBER_OTHER,
+	KYBER_NUM_DOMAINS,
+};
+
+static const char *kyber_domain_names[] = {
+	[KYBER_READ] = "READ",
+	[KYBER_WRITE] = "WRITE",
+	[KYBER_DISCARD] = "DISCARD",
+	[KYBER_OTHER] = "OTHER",
+};
+
+enum {
+	/*
+	 * In order to prevent starvation of synchronous requests by a flood of
+	 * asynchronous requests, we reserve 25% of requests for synchronous
+	 * operations.
+	 */
+	KYBER_ASYNC_PERCENT = 75,
+};
+
+/*
+ * Maximum device-wide depth for each scheduling domain.
+ *
+ * Even for fast devices with lots of tags like NVMe, you can saturate the
+ * device with only a fraction of the maximum possible queue depth. So, we cap
+ * these to a reasonable value.
+ */
+static const unsigned int kyber_depth[] = {
+	[KYBER_READ] = 256,
+	[KYBER_WRITE] = 128,
+	[KYBER_DISCARD] = 64,
+	[KYBER_OTHER] = 16,
+};
+
+/*
+ * Default latency targets for each scheduling domain.
+ */
+static const u64 kyber_latency_targets[] = {
+	[KYBER_READ] = 2ULL * NSEC_PER_MSEC,
+	[KYBER_WRITE] = 10ULL * NSEC_PER_MSEC,
+	[KYBER_DISCARD] = 5ULL * NSEC_PER_SEC,
+};
+
+/*
+ * Batch size (number of requests we'll dispatch in a row) for each scheduling
+ * domain.
+ */
+static const unsigned int kyber_batch_size[] = {
+	[KYBER_READ] = 16,
+	[KYBER_WRITE] = 8,
+	[KYBER_DISCARD] = 1,
+	[KYBER_OTHER] = 1,
+};
+
+/*
+ * Requests latencies are recorded in a histogram with buckets defined relative
+ * to the target latency:
+ *
+ * <= 1/4 * target latency
+ * <= 1/2 * target latency
+ * <= 3/4 * target latency
+ * <= target latency
+ * <= 1 1/4 * target latency
+ * <= 1 1/2 * target latency
+ * <= 1 3/4 * target latency
+ * > 1 3/4 * target latency
+ */
+enum {
+	/*
+	 * The width of the latency histogram buckets is
+	 * 1 / (1 << KYBER_LATENCY_SHIFT) * target latency.
+	 */
+	KYBER_LATENCY_SHIFT = 2,
+	/*
+	 * The first (1 << KYBER_LATENCY_SHIFT) buckets are <= target latency,
+	 * thus, "good".
+	 */
+	KYBER_GOOD_BUCKETS = 1 << KYBER_LATENCY_SHIFT,
+	/* There are also (1 << KYBER_LATENCY_SHIFT) "bad" buckets. */
+	KYBER_LATENCY_BUCKETS = 2 << KYBER_LATENCY_SHIFT,
+};
+
+/*
+ * We measure both the total latency and the I/O latency (i.e., latency after
+ * submitting to the device).
+ */
+enum {
+	KYBER_TOTAL_LATENCY,
+	KYBER_IO_LATENCY,
+};
+
+static const char *kyber_latency_type_names[] = {
+	[KYBER_TOTAL_LATENCY] = "total",
+	[KYBER_IO_LATENCY] = "I/O",
+};
+
+/*
+ * Per-cpu latency histograms: total latency and I/O latency for each scheduling
+ * domain except for KYBER_OTHER.
+ */
+struct kyber_cpu_latency {
+	atomic_t buckets[KYBER_OTHER][2][KYBER_LATENCY_BUCKETS];
+};
+
+/*
+ * There is a same mapping between ctx & hctx and kcq & khd,
+ * we use request->mq_ctx->index_hw to index the kcq in khd.
+ */
+struct kyber_ctx_queue {
+	/*
+	 * Used to ensure operations on rq_list and kcq_map to be an atmoic one.
+	 * Also protect the rqs on rq_list when merge.
+	 */
+	spinlock_t lock;
+	struct list_head rq_list[KYBER_NUM_DOMAINS];
+} ____cacheline_aligned_in_smp;
+
+struct kyber_queue_data {
+	struct request_queue *q;
+
+	/*
+	 * Each scheduling domain has a limited number of in-flight requests
+	 * device-wide, limited by these tokens.
+	 */
+	struct sbitmap_queue domain_tokens[KYBER_NUM_DOMAINS];
+
+	/*
+	 * Async request percentage, converted to per-word depth for
+	 * sbitmap_get_shallow().
+	 */
+	unsigned int async_depth;
+
+	struct kyber_cpu_latency __percpu *cpu_latency;
+
+	/* Timer for stats aggregation and adjusting domain tokens. */
+	struct timer_list timer;
+
+	unsigned int latency_buckets[KYBER_OTHER][2][KYBER_LATENCY_BUCKETS];
+
+	unsigned long latency_timeout[KYBER_OTHER];
+
+	int domain_p99[KYBER_OTHER];
+
+	/* Target latencies in nanoseconds. */
+	u64 latency_targets[KYBER_OTHER];
+};
+
+struct kyber_hctx_data {
+	spinlock_t lock;
+	struct list_head rqs[KYBER_NUM_DOMAINS];
+	unsigned int cur_domain;
+	unsigned int batching;
+	struct kyber_ctx_queue *kcqs;
+	struct sbitmap kcq_map[KYBER_NUM_DOMAINS];
+	struct sbq_wait domain_wait[KYBER_NUM_DOMAINS];
+	struct sbq_wait_state *domain_ws[KYBER_NUM_DOMAINS];
+	atomic_t wait_index[KYBER_NUM_DOMAINS];
+};
+
+static int kyber_domain_wake(wait_queue_entry_t *wait, unsigned mode, int flags,
+			     void *key);
+
+static unsigned int kyber_sched_domain(unsigned int op)
+{
+	switch (op & REQ_OP_MASK) {
+	case REQ_OP_READ:
+		return KYBER_READ;
+	case REQ_OP_WRITE:
+		return KYBER_WRITE;
+	case REQ_OP_DISCARD:
+		return KYBER_DISCARD;
+	default:
+		return KYBER_OTHER;
+	}
+}
+
+static void flush_latency_buckets(struct kyber_queue_data *kqd,
+				  struct kyber_cpu_latency *cpu_latency,
+				  unsigned int sched_domain, unsigned int type)
+{
+	unsigned int *buckets = kqd->latency_buckets[sched_domain][type];
+	atomic_t *cpu_buckets = cpu_latency->buckets[sched_domain][type];
+	unsigned int bucket;
+
+	for (bucket = 0; bucket < KYBER_LATENCY_BUCKETS; bucket++)
+		buckets[bucket] += atomic_xchg(&cpu_buckets[bucket], 0);
+}
+
+/*
+ * Calculate the histogram bucket with the given percentile rank, or -1 if there
+ * aren't enough samples yet.
+ */
+static int calculate_percentile(struct kyber_queue_data *kqd,
+				unsigned int sched_domain, unsigned int type,
+				unsigned int percentile)
+{
+	unsigned int *buckets = kqd->latency_buckets[sched_domain][type];
+	unsigned int bucket, samples = 0, percentile_samples;
+
+	for (bucket = 0; bucket < KYBER_LATENCY_BUCKETS; bucket++)
+		samples += buckets[bucket];
+
+	if (!samples)
+		return -1;
+
+	/*
+	 * We do the calculation once we have 500 samples or one second passes
+	 * since the first sample was recorded, whichever comes first.
+	 */
+	if (!kqd->latency_timeout[sched_domain])
+		kqd->latency_timeout[sched_domain] = max(jiffies + HZ, 1UL);
+	if (samples < 500 &&
+	    time_is_after_jiffies(kqd->latency_timeout[sched_domain])) {
+		return -1;
+	}
+	kqd->latency_timeout[sched_domain] = 0;
+
+	percentile_samples = DIV_ROUND_UP(samples * percentile, 100);
+	for (bucket = 0; bucket < KYBER_LATENCY_BUCKETS - 1; bucket++) {
+		if (buckets[bucket] >= percentile_samples)
+			break;
+		percentile_samples -= buckets[bucket];
+	}
+	memset(buckets, 0, sizeof(kqd->latency_buckets[sched_domain][type]));
+
+	trace_kyber_latency(kqd->q, kyber_domain_names[sched_domain],
+			    kyber_latency_type_names[type], percentile,
+			    bucket + 1, 1 << KYBER_LATENCY_SHIFT, samples);
+
+	return bucket;
+}
+
+static void kyber_resize_domain(struct kyber_queue_data *kqd,
+				unsigned int sched_domain, unsigned int depth)
+{
+	depth = clamp(depth, 1U, kyber_depth[sched_domain]);
+	if (depth != kqd->domain_tokens[sched_domain].sb.depth) {
+		sbitmap_queue_resize(&kqd->domain_tokens[sched_domain], depth);
+		trace_kyber_adjust(kqd->q, kyber_domain_names[sched_domain],
+				   depth);
+	}
+}
+
+static void kyber_timer_fn(struct timer_list *t)
+{
+	struct kyber_queue_data *kqd = from_timer(kqd, t, timer);
+	unsigned int sched_domain;
+	int cpu;
+	bool bad = false;
+
+	/* Sum all of the per-cpu latency histograms. */
+	for_each_online_cpu(cpu) {
+		struct kyber_cpu_latency *cpu_latency;
+
+		cpu_latency = per_cpu_ptr(kqd->cpu_latency, cpu);
+		for (sched_domain = 0; sched_domain < KYBER_OTHER; sched_domain++) {
+			flush_latency_buckets(kqd, cpu_latency, sched_domain,
+					      KYBER_TOTAL_LATENCY);
+			flush_latency_buckets(kqd, cpu_latency, sched_domain,
+					      KYBER_IO_LATENCY);
+		}
+	}
+
+	/*
+	 * Check if any domains have a high I/O latency, which might indicate
+	 * congestion in the device. Note that we use the p90; we don't want to
+	 * be too sensitive to outliers here.
+	 */
+	for (sched_domain = 0; sched_domain < KYBER_OTHER; sched_domain++) {
+		int p90;
+
+		p90 = calculate_percentile(kqd, sched_domain, KYBER_IO_LATENCY,
+					   90);
+		if (p90 >= KYBER_GOOD_BUCKETS)
+			bad = true;
+	}
+
+	/*
+	 * Adjust the scheduling domain depths. If we determined that there was
+	 * congestion, we throttle all domains with good latencies. Either way,
+	 * we ease up on throttling domains with bad latencies.
+	 */
+	for (sched_domain = 0; sched_domain < KYBER_OTHER; sched_domain++) {
+		unsigned int orig_depth, depth;
+		int p99;
+
+		p99 = calculate_percentile(kqd, sched_domain,
+					   KYBER_TOTAL_LATENCY, 99);
+		/*
+		 * This is kind of subtle: different domains will not
+		 * necessarily have enough samples to calculate the latency
+		 * percentiles during the same window, so we have to remember
+		 * the p99 for the next time we observe congestion; once we do,
+		 * we don't want to throttle again until we get more data, so we
+		 * reset it to -1.
+		 */
+		if (bad) {
+			if (p99 < 0)
+				p99 = kqd->domain_p99[sched_domain];
+			kqd->domain_p99[sched_domain] = -1;
+		} else if (p99 >= 0) {
+			kqd->domain_p99[sched_domain] = p99;
+		}
+		if (p99 < 0)
+			continue;
+
+		/*
+		 * If this domain has bad latency, throttle less. Otherwise,
+		 * throttle more iff we determined that there is congestion.
+		 *
+		 * The new depth is scaled linearly with the p99 latency vs the
+		 * latency target. E.g., if the p99 is 3/4 of the target, then
+		 * we throttle down to 3/4 of the current depth, and if the p99
+		 * is 2x the target, then we double the depth.
+		 */
+		if (bad || p99 >= KYBER_GOOD_BUCKETS) {
+			orig_depth = kqd->domain_tokens[sched_domain].sb.depth;
+			depth = (orig_depth * (p99 + 1)) >> KYBER_LATENCY_SHIFT;
+			kyber_resize_domain(kqd, sched_domain, depth);
+		}
+	}
+}
+
+static unsigned int kyber_sched_tags_shift(struct request_queue *q)
+{
+	/*
+	 * All of the hardware queues have the same depth, so we can just grab
+	 * the shift of the first one.
+	 */
+	return q->queue_hw_ctx[0]->sched_tags->bitmap_tags->sb.shift;
+}
+
+static struct kyber_queue_data *kyber_queue_data_alloc(struct request_queue *q)
+{
+	struct kyber_queue_data *kqd;
+	unsigned int shift;
+	int ret = -ENOMEM;
+	int i;
+
+	kqd = kzalloc_node(sizeof(*kqd), GFP_KERNEL, q->node);
+	if (!kqd)
+		goto err;
+
+	kqd->q = q;
+
+	kqd->cpu_latency = alloc_percpu_gfp(struct kyber_cpu_latency,
+					    GFP_KERNEL | __GFP_ZERO);
+	if (!kqd->cpu_latency)
+		goto err_kqd;
+
+	timer_setup(&kqd->timer, kyber_timer_fn, 0);
+
+	for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
+		WARN_ON(!kyber_depth[i]);
+		WARN_ON(!kyber_batch_size[i]);
+		ret = sbitmap_queue_init_node(&kqd->domain_tokens[i],
+					      kyber_depth[i], -1, false,
+					      GFP_KERNEL, q->node);
+		if (ret) {
+			while (--i >= 0)
+				sbitmap_queue_free(&kqd->domain_tokens[i]);
+			goto err_buckets;
+		}
+	}
+
+	for (i = 0; i < KYBER_OTHER; i++) {
+		kqd->domain_p99[i] = -1;
+		kqd->latency_targets[i] = kyber_latency_targets[i];
+	}
+
+	shift = kyber_sched_tags_shift(q);
+	kqd->async_depth = (1U << shift) * KYBER_ASYNC_PERCENT / 100U;
+
+	return kqd;
+
+err_buckets:
+	free_percpu(kqd->cpu_latency);
+err_kqd:
+	kfree(kqd);
+err:
+	return ERR_PTR(ret);
+}
+
+static int kyber_init_sched(struct request_queue *q, struct elevator_type *e)
+{
+	struct kyber_queue_data *kqd;
+	struct elevator_queue *eq;
+
+	eq = elevator_alloc(q, e);
+	if (!eq)
+		return -ENOMEM;
+
+	kqd = kyber_queue_data_alloc(q);
+	if (IS_ERR(kqd)) {
+		kobject_put(&eq->kobj);
+		return PTR_ERR(kqd);
+	}
+
+	blk_stat_enable_accounting(q);
+
+	eq->elevator_data = kqd;
+	q->elevator = eq;
+
+	return 0;
+}
+
+static void kyber_exit_sched(struct elevator_queue *e)
+{
+	struct kyber_queue_data *kqd = e->elevator_data;
+	int i;
+
+	del_timer_sync(&kqd->timer);
+
+	for (i = 0; i < KYBER_NUM_DOMAINS; i++)
+		sbitmap_queue_free(&kqd->domain_tokens[i]);
+	free_percpu(kqd->cpu_latency);
+	kfree(kqd);
+}
+
+static void kyber_ctx_queue_init(struct kyber_ctx_queue *kcq)
+{
+	unsigned int i;
+
+	spin_lock_init(&kcq->lock);
+	for (i = 0; i < KYBER_NUM_DOMAINS; i++)
+		INIT_LIST_HEAD(&kcq->rq_list[i]);
+}
+
+static int kyber_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
+{
+	struct kyber_queue_data *kqd = hctx->queue->elevator->elevator_data;
+	struct kyber_hctx_data *khd;
+	int i;
+
+	khd = kmalloc_node(sizeof(*khd), GFP_KERNEL, hctx->numa_node);
+	if (!khd)
+		return -ENOMEM;
+
+	khd->kcqs = kmalloc_array_node(hctx->nr_ctx,
+				       sizeof(struct kyber_ctx_queue),
+				       GFP_KERNEL, hctx->numa_node);
+	if (!khd->kcqs)
+		goto err_khd;
+
+	for (i = 0; i < hctx->nr_ctx; i++)
+		kyber_ctx_queue_init(&khd->kcqs[i]);
+
+	for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
+		if (sbitmap_init_node(&khd->kcq_map[i], hctx->nr_ctx,
+				      ilog2(8), GFP_KERNEL, hctx->numa_node)) {
+			while (--i >= 0)
+				sbitmap_free(&khd->kcq_map[i]);
+			goto err_kcqs;
+		}
+	}
+
+	spin_lock_init(&khd->lock);
+
+	for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
+		INIT_LIST_HEAD(&khd->rqs[i]);
+		khd->domain_wait[i].sbq = NULL;
+		init_waitqueue_func_entry(&khd->domain_wait[i].wait,
+					  kyber_domain_wake);
+		khd->domain_wait[i].wait.private = hctx;
+		INIT_LIST_HEAD(&khd->domain_wait[i].wait.entry);
+		atomic_set(&khd->wait_index[i], 0);
+	}
+
+	khd->cur_domain = 0;
+	khd->batching = 0;
+
+	hctx->sched_data = khd;
+	sbitmap_queue_min_shallow_depth(hctx->sched_tags->bitmap_tags,
+					kqd->async_depth);
+
+	return 0;
+
+err_kcqs:
+	kfree(khd->kcqs);
+err_khd:
+	kfree(khd);
+	return -ENOMEM;
+}
+
+static void kyber_exit_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
+{
+	struct kyber_hctx_data *khd = hctx->sched_data;
+	int i;
+
+	for (i = 0; i < KYBER_NUM_DOMAINS; i++)
+		sbitmap_free(&khd->kcq_map[i]);
+	kfree(khd->kcqs);
+	kfree(hctx->sched_data);
+}
+
+static int rq_get_domain_token(struct request *rq)
+{
+	return (long)rq->elv.priv[0];
+}
+
+static void rq_set_domain_token(struct request *rq, int token)
+{
+	rq->elv.priv[0] = (void *)(long)token;
+}
+
+static void rq_clear_domain_token(struct kyber_queue_data *kqd,
+				  struct request *rq)
+{
+	unsigned int sched_domain;
+	int nr;
+
+	nr = rq_get_domain_token(rq);
+	if (nr != -1) {
+		sched_domain = kyber_sched_domain(rq->cmd_flags);
+		sbitmap_queue_clear(&kqd->domain_tokens[sched_domain], nr,
+				    rq->mq_ctx->cpu);
+	}
+}
+
+static void kyber_limit_depth(unsigned int op, struct blk_mq_alloc_data *data)
+{
+	/*
+	 * We use the scheduler tags as per-hardware queue queueing tokens.
+	 * Async requests can be limited at this stage.
+	 */
+	if (!op_is_sync(op)) {
+		struct kyber_queue_data *kqd = data->q->elevator->elevator_data;
+
+		data->shallow_depth = kqd->async_depth;
+	}
+}
+
+static bool kyber_bio_merge(struct request_queue *q, struct bio *bio,
+		unsigned int nr_segs)
+{
+	struct blk_mq_ctx *ctx = blk_mq_get_ctx(q);
+	struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, bio->bi_opf, ctx);
+	struct kyber_hctx_data *khd = hctx->sched_data;
+	struct kyber_ctx_queue *kcq = &khd->kcqs[ctx->index_hw[hctx->type]];
+	unsigned int sched_domain = kyber_sched_domain(bio->bi_opf);
+	struct list_head *rq_list = &kcq->rq_list[sched_domain];
+	bool merged;
+
+	spin_lock(&kcq->lock);
+	merged = blk_bio_list_merge(hctx->queue, rq_list, bio, nr_segs);
+	spin_unlock(&kcq->lock);
+
+	return merged;
+}
+
+static void kyber_prepare_request(struct request *rq)
+{
+	rq_set_domain_token(rq, -1);
+}
+
+static void kyber_insert_requests(struct blk_mq_hw_ctx *hctx,
+				  struct list_head *rq_list, bool at_head)
+{
+	struct kyber_hctx_data *khd = hctx->sched_data;
+	struct request *rq, *next;
+
+	list_for_each_entry_safe(rq, next, rq_list, queuelist) {
+		unsigned int sched_domain = kyber_sched_domain(rq->cmd_flags);
+		struct kyber_ctx_queue *kcq = &khd->kcqs[rq->mq_ctx->index_hw[hctx->type]];
+		struct list_head *head = &kcq->rq_list[sched_domain];
+
+		spin_lock(&kcq->lock);
+		if (at_head)
+			list_move(&rq->queuelist, head);
+		else
+			list_move_tail(&rq->queuelist, head);
+		sbitmap_set_bit(&khd->kcq_map[sched_domain],
+				rq->mq_ctx->index_hw[hctx->type]);
+		blk_mq_sched_request_inserted(rq);
+		spin_unlock(&kcq->lock);
+	}
+}
+
+static void kyber_finish_request(struct request *rq)
+{
+	struct kyber_queue_data *kqd = rq->q->elevator->elevator_data;
+
+	rq_clear_domain_token(kqd, rq);
+}
+
+static void add_latency_sample(struct kyber_cpu_latency *cpu_latency,
+			       unsigned int sched_domain, unsigned int type,
+			       u64 target, u64 latency)
+{
+	unsigned int bucket;
+	u64 divisor;
+
+	if (latency > 0) {
+		divisor = max_t(u64, target >> KYBER_LATENCY_SHIFT, 1);
+		bucket = min_t(unsigned int, div64_u64(latency - 1, divisor),
+			       KYBER_LATENCY_BUCKETS - 1);
+	} else {
+		bucket = 0;
+	}
+
+	atomic_inc(&cpu_latency->buckets[sched_domain][type][bucket]);
+}
+
+static void kyber_completed_request(struct request *rq, u64 now)
+{
+	struct kyber_queue_data *kqd = rq->q->elevator->elevator_data;
+	struct kyber_cpu_latency *cpu_latency;
+	unsigned int sched_domain;
+	u64 target;
+
+	sched_domain = kyber_sched_domain(rq->cmd_flags);
+	if (sched_domain == KYBER_OTHER)
+		return;
+
+	cpu_latency = get_cpu_ptr(kqd->cpu_latency);
+	target = kqd->latency_targets[sched_domain];
+	add_latency_sample(cpu_latency, sched_domain, KYBER_TOTAL_LATENCY,
+			   target, now - rq->start_time_ns);
+	add_latency_sample(cpu_latency, sched_domain, KYBER_IO_LATENCY, target,
+			   now - rq->io_start_time_ns);
+	put_cpu_ptr(kqd->cpu_latency);
+
+	timer_reduce(&kqd->timer, jiffies + HZ / 10);
+}
+
+struct flush_kcq_data {
+	struct kyber_hctx_data *khd;
+	unsigned int sched_domain;
+	struct list_head *list;
+};
+
+static bool flush_busy_kcq(struct sbitmap *sb, unsigned int bitnr, void *data)
+{
+	struct flush_kcq_data *flush_data = data;
+	struct kyber_ctx_queue *kcq = &flush_data->khd->kcqs[bitnr];
+
+	spin_lock(&kcq->lock);
+	list_splice_tail_init(&kcq->rq_list[flush_data->sched_domain],
+			      flush_data->list);
+	sbitmap_clear_bit(sb, bitnr);
+	spin_unlock(&kcq->lock);
+
+	return true;
+}
+
+static void kyber_flush_busy_kcqs(struct kyber_hctx_data *khd,
+				  unsigned int sched_domain,
+				  struct list_head *list)
+{
+	struct flush_kcq_data data = {
+		.khd = khd,
+		.sched_domain = sched_domain,
+		.list = list,
+	};
+
+	sbitmap_for_each_set(&khd->kcq_map[sched_domain],
+			     flush_busy_kcq, &data);
+}
+
+static int kyber_domain_wake(wait_queue_entry_t *wqe, unsigned mode, int flags,
+			     void *key)
+{
+	struct blk_mq_hw_ctx *hctx = READ_ONCE(wqe->private);
+	struct sbq_wait *wait = container_of(wqe, struct sbq_wait, wait);
+
+	sbitmap_del_wait_queue(wait);
+	blk_mq_run_hw_queue(hctx, true);
+	return 1;
+}
+
+static int kyber_get_domain_token(struct kyber_queue_data *kqd,
+				  struct kyber_hctx_data *khd,
+				  struct blk_mq_hw_ctx *hctx)
+{
+	unsigned int sched_domain = khd->cur_domain;
+	struct sbitmap_queue *domain_tokens = &kqd->domain_tokens[sched_domain];
+	struct sbq_wait *wait = &khd->domain_wait[sched_domain];
+	struct sbq_wait_state *ws;
+	int nr;
+
+	nr = __sbitmap_queue_get(domain_tokens);
+
+	/*
+	 * If we failed to get a domain token, make sure the hardware queue is
+	 * run when one becomes available. Note that this is serialized on
+	 * khd->lock, but we still need to be careful about the waker.
+	 */
+	if (nr < 0 && list_empty_careful(&wait->wait.entry)) {
+		ws = sbq_wait_ptr(domain_tokens,
+				  &khd->wait_index[sched_domain]);
+		khd->domain_ws[sched_domain] = ws;
+		sbitmap_add_wait_queue(domain_tokens, ws, wait);
+
+		/*
+		 * Try again in case a token was freed before we got on the wait
+		 * queue.
+		 */
+		nr = __sbitmap_queue_get(domain_tokens);
+	}
+
+	/*
+	 * If we got a token while we were on the wait queue, remove ourselves
+	 * from the wait queue to ensure that all wake ups make forward
+	 * progress. It's possible that the waker already deleted the entry
+	 * between the !list_empty_careful() check and us grabbing the lock, but
+	 * list_del_init() is okay with that.
+	 */
+	if (nr >= 0 && !list_empty_careful(&wait->wait.entry)) {
+		ws = khd->domain_ws[sched_domain];
+		spin_lock_irq(&ws->wait.lock);
+		sbitmap_del_wait_queue(wait);
+		spin_unlock_irq(&ws->wait.lock);
+	}
+
+	return nr;
+}
+
+static struct request *
+kyber_dispatch_cur_domain(struct kyber_queue_data *kqd,
+			  struct kyber_hctx_data *khd,
+			  struct blk_mq_hw_ctx *hctx)
+{
+	struct list_head *rqs;
+	struct request *rq;
+	int nr;
+
+	rqs = &khd->rqs[khd->cur_domain];
+
+	/*
+	 * If we already have a flushed request, then we just need to get a
+	 * token for it. Otherwise, if there are pending requests in the kcqs,
+	 * flush the kcqs, but only if we can get a token. If not, we should
+	 * leave the requests in the kcqs so that they can be merged. Note that
+	 * khd->lock serializes the flushes, so if we observed any bit set in
+	 * the kcq_map, we will always get a request.
+	 */
+	rq = list_first_entry_or_null(rqs, struct request, queuelist);
+	if (rq) {
+		nr = kyber_get_domain_token(kqd, khd, hctx);
+		if (nr >= 0) {
+			khd->batching++;
+			rq_set_domain_token(rq, nr);
+			list_del_init(&rq->queuelist);
+			return rq;
+		} else {
+			trace_kyber_throttled(kqd->q,
+					      kyber_domain_names[khd->cur_domain]);
+		}
+	} else if (sbitmap_any_bit_set(&khd->kcq_map[khd->cur_domain])) {
+		nr = kyber_get_domain_token(kqd, khd, hctx);
+		if (nr >= 0) {
+			kyber_flush_busy_kcqs(khd, khd->cur_domain, rqs);
+			rq = list_first_entry(rqs, struct request, queuelist);
+			khd->batching++;
+			rq_set_domain_token(rq, nr);
+			list_del_init(&rq->queuelist);
+			return rq;
+		} else {
+			trace_kyber_throttled(kqd->q,
+					      kyber_domain_names[khd->cur_domain]);
+		}
+	}
+
+	/* There were either no pending requests or no tokens. */
+	return NULL;
+}
+
+static struct request *kyber_dispatch_request(struct blk_mq_hw_ctx *hctx)
+{
+	struct kyber_queue_data *kqd = hctx->queue->elevator->elevator_data;
+	struct kyber_hctx_data *khd = hctx->sched_data;
+	struct request *rq;
+	int i;
+
+	spin_lock(&khd->lock);
+
+	/*
+	 * First, if we are still entitled to batch, try to dispatch a request
+	 * from the batch.
+	 */
+	if (khd->batching < kyber_batch_size[khd->cur_domain]) {
+		rq = kyber_dispatch_cur_domain(kqd, khd, hctx);
+		if (rq)
+			goto out;
+	}
+
+	/*
+	 * Either,
+	 * 1. We were no longer entitled to a batch.
+	 * 2. The domain we were batching didn't have any requests.
+	 * 3. The domain we were batching was out of tokens.
+	 *
+	 * Start another batch. Note that this wraps back around to the original
+	 * domain if no other domains have requests or tokens.
+	 */
+	khd->batching = 0;
+	for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
+		if (khd->cur_domain == KYBER_NUM_DOMAINS - 1)
+			khd->cur_domain = 0;
+		else
+			khd->cur_domain++;
+
+		rq = kyber_dispatch_cur_domain(kqd, khd, hctx);
+		if (rq)
+			goto out;
+	}
+
+	rq = NULL;
+out:
+	spin_unlock(&khd->lock);
+	return rq;
+}
+
+static bool kyber_has_work(struct blk_mq_hw_ctx *hctx)
+{
+	struct kyber_hctx_data *khd = hctx->sched_data;
+	int i;
+
+	for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
+		if (!list_empty_careful(&khd->rqs[i]) ||
+		    sbitmap_any_bit_set(&khd->kcq_map[i]))
+			return true;
+	}
+
+	return false;
+}
+
+#define KYBER_LAT_SHOW_STORE(domain, name)				\
+static ssize_t kyber_##name##_lat_show(struct elevator_queue *e,	\
+				       char *page)			\
+{									\
+	struct kyber_queue_data *kqd = e->elevator_data;		\
+									\
+	return sprintf(page, "%llu\n", kqd->latency_targets[domain]);	\
+}									\
+									\
+static ssize_t kyber_##name##_lat_store(struct elevator_queue *e,	\
+					const char *page, size_t count)	\
+{									\
+	struct kyber_queue_data *kqd = e->elevator_data;		\
+	unsigned long long nsec;					\
+	int ret;							\
+									\
+	ret = kstrtoull(page, 10, &nsec);				\
+	if (ret)							\
+		return ret;						\
+									\
+	kqd->latency_targets[domain] = nsec;				\
+									\
+	return count;							\
+}
+KYBER_LAT_SHOW_STORE(KYBER_READ, read);
+KYBER_LAT_SHOW_STORE(KYBER_WRITE, write);
+#undef KYBER_LAT_SHOW_STORE
+
+#define KYBER_LAT_ATTR(op) __ATTR(op##_lat_nsec, 0644, kyber_##op##_lat_show, kyber_##op##_lat_store)
+static struct elv_fs_entry kyber_sched_attrs[] = {
+	KYBER_LAT_ATTR(read),
+	KYBER_LAT_ATTR(write),
+	__ATTR_NULL
+};
+#undef KYBER_LAT_ATTR
+
+#ifdef CONFIG_BLK_DEBUG_FS
+#define KYBER_DEBUGFS_DOMAIN_ATTRS(domain, name)			\
+static int kyber_##name##_tokens_show(void *data, struct seq_file *m)	\
+{									\
+	struct request_queue *q = data;					\
+	struct kyber_queue_data *kqd = q->elevator->elevator_data;	\
+									\
+	sbitmap_queue_show(&kqd->domain_tokens[domain], m);		\
+	return 0;							\
+}									\
+									\
+static void *kyber_##name##_rqs_start(struct seq_file *m, loff_t *pos)	\
+	__acquires(&khd->lock)						\
+{									\
+	struct blk_mq_hw_ctx *hctx = m->private;			\
+	struct kyber_hctx_data *khd = hctx->sched_data;			\
+									\
+	spin_lock(&khd->lock);						\
+	return seq_list_start(&khd->rqs[domain], *pos);			\
+}									\
+									\
+static void *kyber_##name##_rqs_next(struct seq_file *m, void *v,	\
+				     loff_t *pos)			\
+{									\
+	struct blk_mq_hw_ctx *hctx = m->private;			\
+	struct kyber_hctx_data *khd = hctx->sched_data;			\
+									\
+	return seq_list_next(v, &khd->rqs[domain], pos);		\
+}									\
+									\
+static void kyber_##name##_rqs_stop(struct seq_file *m, void *v)	\
+	__releases(&khd->lock)						\
+{									\
+	struct blk_mq_hw_ctx *hctx = m->private;			\
+	struct kyber_hctx_data *khd = hctx->sched_data;			\
+									\
+	spin_unlock(&khd->lock);					\
+}									\
+									\
+static const struct seq_operations kyber_##name##_rqs_seq_ops = {	\
+	.start	= kyber_##name##_rqs_start,				\
+	.next	= kyber_##name##_rqs_next,				\
+	.stop	= kyber_##name##_rqs_stop,				\
+	.show	= blk_mq_debugfs_rq_show,				\
+};									\
+									\
+static int kyber_##name##_waiting_show(void *data, struct seq_file *m)	\
+{									\
+	struct blk_mq_hw_ctx *hctx = data;				\
+	struct kyber_hctx_data *khd = hctx->sched_data;			\
+	wait_queue_entry_t *wait = &khd->domain_wait[domain].wait;	\
+									\
+	seq_printf(m, "%d\n", !list_empty_careful(&wait->entry));	\
+	return 0;							\
+}
+KYBER_DEBUGFS_DOMAIN_ATTRS(KYBER_READ, read)
+KYBER_DEBUGFS_DOMAIN_ATTRS(KYBER_WRITE, write)
+KYBER_DEBUGFS_DOMAIN_ATTRS(KYBER_DISCARD, discard)
+KYBER_DEBUGFS_DOMAIN_ATTRS(KYBER_OTHER, other)
+#undef KYBER_DEBUGFS_DOMAIN_ATTRS
+
+static int kyber_async_depth_show(void *data, struct seq_file *m)
+{
+	struct request_queue *q = data;
+	struct kyber_queue_data *kqd = q->elevator->elevator_data;
+
+	seq_printf(m, "%u\n", kqd->async_depth);
+	return 0;
+}
+
+static int kyber_cur_domain_show(void *data, struct seq_file *m)
+{
+	struct blk_mq_hw_ctx *hctx = data;
+	struct kyber_hctx_data *khd = hctx->sched_data;
+
+	seq_printf(m, "%s\n", kyber_domain_names[khd->cur_domain]);
+	return 0;
+}
+
+static int kyber_batching_show(void *data, struct seq_file *m)
+{
+	struct blk_mq_hw_ctx *hctx = data;
+	struct kyber_hctx_data *khd = hctx->sched_data;
+
+	seq_printf(m, "%u\n", khd->batching);
+	return 0;
+}
+
+#define KYBER_QUEUE_DOMAIN_ATTRS(name)	\
+	{#name "_tokens", 0400, kyber_##name##_tokens_show}
+static const struct blk_mq_debugfs_attr kyber_queue_debugfs_attrs[] = {
+	KYBER_QUEUE_DOMAIN_ATTRS(read),
+	KYBER_QUEUE_DOMAIN_ATTRS(write),
+	KYBER_QUEUE_DOMAIN_ATTRS(discard),
+	KYBER_QUEUE_DOMAIN_ATTRS(other),
+	{"async_depth", 0400, kyber_async_depth_show},
+	{},
+};
+#undef KYBER_QUEUE_DOMAIN_ATTRS
+
+#define KYBER_HCTX_DOMAIN_ATTRS(name)					\
+	{#name "_rqs", 0400, .seq_ops = &kyber_##name##_rqs_seq_ops},	\
+	{#name "_waiting", 0400, kyber_##name##_waiting_show}
+static const struct blk_mq_debugfs_attr kyber_hctx_debugfs_attrs[] = {
+	KYBER_HCTX_DOMAIN_ATTRS(read),
+	KYBER_HCTX_DOMAIN_ATTRS(write),
+	KYBER_HCTX_DOMAIN_ATTRS(discard),
+	KYBER_HCTX_DOMAIN_ATTRS(other),
+	{"cur_domain", 0400, kyber_cur_domain_show},
+	{"batching", 0400, kyber_batching_show},
+	{},
+};
+#undef KYBER_HCTX_DOMAIN_ATTRS
+#endif
+
+static struct elevator_type kyber_sched = {
+	.ops = {
+		.init_sched = kyber_init_sched,
+		.exit_sched = kyber_exit_sched,
+		.init_hctx = kyber_init_hctx,
+		.exit_hctx = kyber_exit_hctx,
+		.limit_depth = kyber_limit_depth,
+		.bio_merge = kyber_bio_merge,
+		.prepare_request = kyber_prepare_request,
+		.insert_requests = kyber_insert_requests,
+		.finish_request = kyber_finish_request,
+		.requeue_request = kyber_finish_request,
+		.completed_request = kyber_completed_request,
+		.dispatch_request = kyber_dispatch_request,
+		.has_work = kyber_has_work,
+	},
+#ifdef CONFIG_BLK_DEBUG_FS
+	.queue_debugfs_attrs = kyber_queue_debugfs_attrs,
+	.hctx_debugfs_attrs = kyber_hctx_debugfs_attrs,
+#endif
+	.elevator_attrs = kyber_sched_attrs,
+	.elevator_name = "kyber",
+	.elevator_owner = THIS_MODULE,
+};
+
+static int __init kyber_init(void)
+{
+	return elv_register(&kyber_sched);
+}
+
+static void __exit kyber_exit(void)
+{
+	elv_unregister(&kyber_sched);
+}
+
+module_init(kyber_init);
+module_exit(kyber_exit);
+
+MODULE_AUTHOR("Omar Sandoval");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Kyber I/O scheduler");