1 files changed, 719 insertions, 0 deletions

diff --git a/block/kyber-iosched.c b/block/kyber-iosched.c
new file mode 100644
index 000000000000..fe4af5b97c0e
--- /dev/null
+++ b/block/kyber-iosched.c
@@ -0,0 +1,719 @@
+/*
+ * The Kyber I/O scheduler. Controls latency by throttling queue depths using
+ * scalable techniques.
+ *
+ * Copyright (C) 2017 Facebook
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#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-sched.h"
+#include "blk-mq-tag.h"
+#include "blk-stat.h"
+
+/* Scheduling domains. */
+enum {
+	KYBER_READ,
+	KYBER_SYNC_WRITE,
+	KYBER_OTHER, /* Async writes, discard, etc. */
+	KYBER_NUM_DOMAINS,
+};
+
+enum {
+	KYBER_MIN_DEPTH = 256,
+
+	/*
+	 * 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,
+};
+
+/*
+ * Initial device-wide depths 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_SYNC_WRITE] = 128,
+	[KYBER_OTHER] = 64,
+};
+
+/*
+ * Scheduling domain batch sizes. We favor reads.
+ */
+static const unsigned int kyber_batch_size[] = {
+	[KYBER_READ] = 16,
+	[KYBER_SYNC_WRITE] = 8,
+	[KYBER_OTHER] = 8,
+};
+
+struct kyber_queue_data {
+	struct request_queue *q;
+
+	struct blk_stat_callback *cb;
+
+	/*
+	 * The device is divided into multiple scheduling domains based on the
+	 * request type. Each domain has a fixed number of in-flight requests of
+	 * that type 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;
+
+	/* Target latencies in nanoseconds. */
+	u64 read_lat_nsec, write_lat_nsec;
+};
+
+struct kyber_hctx_data {
+	spinlock_t lock;
+	struct list_head rqs[KYBER_NUM_DOMAINS];
+	unsigned int cur_domain;
+	unsigned int batching;
+	wait_queue_t domain_wait[KYBER_NUM_DOMAINS];
+	atomic_t wait_index[KYBER_NUM_DOMAINS];
+};
+
+static unsigned int rq_sched_domain(const struct request *rq)
+{
+	unsigned int op = rq->cmd_flags;
+
+	if ((op & REQ_OP_MASK) == REQ_OP_READ)
+		return KYBER_READ;
+	else if ((op & REQ_OP_MASK) == REQ_OP_WRITE && op_is_sync(op))
+		return KYBER_SYNC_WRITE;
+	else
+		return KYBER_OTHER;
+}
+
+enum {
+	NONE = 0,
+	GOOD = 1,
+	GREAT = 2,
+	BAD = -1,
+	AWFUL = -2,
+};
+
+#define IS_GOOD(status) ((status) > 0)
+#define IS_BAD(status) ((status) < 0)
+
+static int kyber_lat_status(struct blk_stat_callback *cb,
+			    unsigned int sched_domain, u64 target)
+{
+	u64 latency;
+
+	if (!cb->stat[sched_domain].nr_samples)
+		return NONE;
+
+	latency = cb->stat[sched_domain].mean;
+	if (latency >= 2 * target)
+		return AWFUL;
+	else if (latency > target)
+		return BAD;
+	else if (latency <= target / 2)
+		return GREAT;
+	else /* (latency <= target) */
+		return GOOD;
+}
+
+/*
+ * Adjust the read or synchronous write depth given the status of reads and
+ * writes. The goal is that the latencies of the two domains are fair (i.e., if
+ * one is good, then the other is good).
+ */
+static void kyber_adjust_rw_depth(struct kyber_queue_data *kqd,
+				  unsigned int sched_domain, int this_status,
+				  int other_status)
+{
+	unsigned int orig_depth, depth;
+
+	/*
+	 * If this domain had no samples, or reads and writes are both good or
+	 * both bad, don't adjust the depth.
+	 */
+	if (this_status == NONE ||
+	    (IS_GOOD(this_status) && IS_GOOD(other_status)) ||
+	    (IS_BAD(this_status) && IS_BAD(other_status)))
+		return;
+
+	orig_depth = depth = kqd->domain_tokens[sched_domain].sb.depth;
+
+	if (other_status == NONE) {
+		depth++;
+	} else {
+		switch (this_status) {
+		case GOOD:
+			if (other_status == AWFUL)
+				depth -= max(depth / 4, 1U);
+			else
+				depth -= max(depth / 8, 1U);
+			break;
+		case GREAT:
+			if (other_status == AWFUL)
+				depth /= 2;
+			else
+				depth -= max(depth / 4, 1U);
+			break;
+		case BAD:
+			depth++;
+			break;
+		case AWFUL:
+			if (other_status == GREAT)
+				depth += 2;
+			else
+				depth++;
+			break;
+		}
+	}
+
+	depth = clamp(depth, 1U, kyber_depth[sched_domain]);
+	if (depth != orig_depth)
+		sbitmap_queue_resize(&kqd->domain_tokens[sched_domain], depth);
+}
+
+/*
+ * Adjust the depth of other requests given the status of reads and synchronous
+ * writes. As long as either domain is doing fine, we don't throttle, but if
+ * both domains are doing badly, we throttle heavily.
+ */
+static void kyber_adjust_other_depth(struct kyber_queue_data *kqd,
+				     int read_status, int write_status,
+				     bool have_samples)
+{
+	unsigned int orig_depth, depth;
+	int status;
+
+	orig_depth = depth = kqd->domain_tokens[KYBER_OTHER].sb.depth;
+
+	if (read_status == NONE && write_status == NONE) {
+		depth += 2;
+	} else if (have_samples) {
+		if (read_status == NONE)
+			status = write_status;
+		else if (write_status == NONE)
+			status = read_status;
+		else
+			status = max(read_status, write_status);
+		switch (status) {
+		case GREAT:
+			depth += 2;
+			break;
+		case GOOD:
+			depth++;
+			break;
+		case BAD:
+			depth -= max(depth / 4, 1U);
+			break;
+		case AWFUL:
+			depth /= 2;
+			break;
+		}
+	}
+
+	depth = clamp(depth, 1U, kyber_depth[KYBER_OTHER]);
+	if (depth != orig_depth)
+		sbitmap_queue_resize(&kqd->domain_tokens[KYBER_OTHER], depth);
+}
+
+/*
+ * Apply heuristics for limiting queue depths based on gathered latency
+ * statistics.
+ */
+static void kyber_stat_timer_fn(struct blk_stat_callback *cb)
+{
+	struct kyber_queue_data *kqd = cb->data;
+	int read_status, write_status;
+
+	read_status = kyber_lat_status(cb, KYBER_READ, kqd->read_lat_nsec);
+	write_status = kyber_lat_status(cb, KYBER_SYNC_WRITE, kqd->write_lat_nsec);
+
+	kyber_adjust_rw_depth(kqd, KYBER_READ, read_status, write_status);
+	kyber_adjust_rw_depth(kqd, KYBER_SYNC_WRITE, write_status, read_status);
+	kyber_adjust_other_depth(kqd, read_status, write_status,
+				 cb->stat[KYBER_OTHER].nr_samples != 0);
+
+	/*
+	 * Continue monitoring latencies if we aren't hitting the targets or
+	 * we're still throttling other requests.
+	 */
+	if (!blk_stat_is_active(kqd->cb) &&
+	    ((IS_BAD(read_status) || IS_BAD(write_status) ||
+	      kqd->domain_tokens[KYBER_OTHER].sb.depth < kyber_depth[KYBER_OTHER])))
+		blk_stat_activate_msecs(kqd->cb, 100);
+}
+
+static unsigned int kyber_sched_tags_shift(struct kyber_queue_data *kqd)
+{
+	/*
+	 * All of the hardware queues have the same depth, so we can just grab
+	 * the shift of the first one.
+	 */
+	return kqd->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 max_tokens;
+	unsigned int shift;
+	int ret = -ENOMEM;
+	int i;
+
+	kqd = kmalloc_node(sizeof(*kqd), GFP_KERNEL, q->node);
+	if (!kqd)
+		goto err;
+	kqd->q = q;
+
+	kqd->cb = blk_stat_alloc_callback(kyber_stat_timer_fn, rq_sched_domain,
+					  KYBER_NUM_DOMAINS, kqd);
+	if (!kqd->cb)
+		goto err_kqd;
+
+	/*
+	 * The maximum number of tokens for any scheduling domain is at least
+	 * the queue depth of a single hardware queue. If the hardware doesn't
+	 * have many tags, still provide a reasonable number.
+	 */
+	max_tokens = max_t(unsigned int, q->tag_set->queue_depth,
+			   KYBER_MIN_DEPTH);
+	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],
+					      max_tokens, -1, false, GFP_KERNEL,
+					      q->node);
+		if (ret) {
+			while (--i >= 0)
+				sbitmap_queue_free(&kqd->domain_tokens[i]);
+			goto err_cb;
+		}
+		sbitmap_queue_resize(&kqd->domain_tokens[i], kyber_depth[i]);
+	}
+
+	shift = kyber_sched_tags_shift(kqd);
+	kqd->async_depth = (1U << shift) * KYBER_ASYNC_PERCENT / 100U;
+
+	kqd->read_lat_nsec = 2000000ULL;
+	kqd->write_lat_nsec = 10000000ULL;
+
+	return kqd;
+
+err_cb:
+	blk_stat_free_callback(kqd->cb);
+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);
+	}
+
+	eq->elevator_data = kqd;
+	q->elevator = eq;
+
+	blk_stat_add_callback(q, kqd->cb);
+
+	return 0;
+}
+
+static void kyber_exit_sched(struct elevator_queue *e)
+{
+	struct kyber_queue_data *kqd = e->elevator_data;
+	struct request_queue *q = kqd->q;
+	int i;
+
+	blk_stat_remove_callback(q, kqd->cb);
+
+	for (i = 0; i < KYBER_NUM_DOMAINS; i++)
+		sbitmap_queue_free(&kqd->domain_tokens[i]);
+	blk_stat_free_callback(kqd->cb);
+	kfree(kqd);
+}
+
+static int kyber_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
+{
+	struct kyber_hctx_data *khd;
+	int i;
+
+	khd = kmalloc_node(sizeof(*khd), GFP_KERNEL, hctx->numa_node);
+	if (!khd)
+		return -ENOMEM;
+
+	spin_lock_init(&khd->lock);
+
+	for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
+		INIT_LIST_HEAD(&khd->rqs[i]);
+		INIT_LIST_HEAD(&khd->domain_wait[i].task_list);
+		atomic_set(&khd->wait_index[i], 0);
+	}
+
+	khd->cur_domain = 0;
+	khd->batching = 0;
+
+	hctx->sched_data = khd;
+
+	return 0;
+}
+
+static void kyber_exit_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
+{
+	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 = rq_sched_domain(rq);
+		sbitmap_queue_clear(&kqd->domain_tokens[sched_domain], nr,
+				    rq->mq_ctx->cpu);
+	}
+}
+
+static struct request *kyber_get_request(struct request_queue *q,
+					 unsigned int op,
+					 struct blk_mq_alloc_data *data)
+{
+	struct kyber_queue_data *kqd = q->elevator->elevator_data;
+	struct request *rq;
+
+	/*
+	 * We use the scheduler tags as per-hardware queue queueing tokens.
+	 * Async requests can be limited at this stage.
+	 */
+	if (!op_is_sync(op))
+		data->shallow_depth = kqd->async_depth;
+
+	rq = __blk_mq_alloc_request(data, op);
+	if (rq)
+		rq_set_domain_token(rq, -1);
+	return rq;
+}
+
+static void kyber_put_request(struct request *rq)
+{
+	struct request_queue *q = rq->q;
+	struct kyber_queue_data *kqd = q->elevator->elevator_data;
+
+	rq_clear_domain_token(kqd, rq);
+	blk_mq_finish_request(rq);
+}
+
+static void kyber_completed_request(struct request *rq)
+{
+	struct request_queue *q = rq->q;
+	struct kyber_queue_data *kqd = q->elevator->elevator_data;
+	unsigned int sched_domain;
+	u64 now, latency, target;
+
+	/*
+	 * Check if this request met our latency goal. If not, quickly gather
+	 * some statistics and start throttling.
+	 */
+	sched_domain = rq_sched_domain(rq);
+	switch (sched_domain) {
+	case KYBER_READ:
+		target = kqd->read_lat_nsec;
+		break;
+	case KYBER_SYNC_WRITE:
+		target = kqd->write_lat_nsec;
+		break;
+	default:
+		return;
+	}
+
+	/* If we are already monitoring latencies, don't check again. */
+	if (blk_stat_is_active(kqd->cb))
+		return;
+
+	now = __blk_stat_time(ktime_to_ns(ktime_get()));
+	if (now < blk_stat_time(&rq->issue_stat))
+		return;
+
+	latency = now - blk_stat_time(&rq->issue_stat);
+
+	if (latency > target)
+		blk_stat_activate_msecs(kqd->cb, 10);
+}
+
+static void kyber_flush_busy_ctxs(struct kyber_hctx_data *khd,
+				  struct blk_mq_hw_ctx *hctx)
+{
+	LIST_HEAD(rq_list);
+	struct request *rq, *next;
+
+	blk_mq_flush_busy_ctxs(hctx, &rq_list);
+	list_for_each_entry_safe(rq, next, &rq_list, queuelist) {
+		unsigned int sched_domain;
+
+		sched_domain = rq_sched_domain(rq);
+		list_move_tail(&rq->queuelist, &khd->rqs[sched_domain]);
+	}
+}
+
+static int kyber_domain_wake(wait_queue_t *wait, unsigned mode, int flags,
+			     void *key)
+{
+	struct blk_mq_hw_ctx *hctx = READ_ONCE(wait->private);
+
+	list_del_init(&wait->task_list);
+	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];
+	wait_queue_t *wait = &khd->domain_wait[sched_domain];
+	struct sbq_wait_state *ws;
+	int nr;
+
+	nr = __sbitmap_queue_get(domain_tokens);
+	if (nr >= 0)
+		return nr;
+
+	/*
+	 * 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 (list_empty_careful(&wait->task_list)) {
+		init_waitqueue_func_entry(wait, kyber_domain_wake);
+		wait->private = hctx;
+		ws = sbq_wait_ptr(domain_tokens,
+				  &khd->wait_index[sched_domain]);
+		add_wait_queue(&ws->wait, wait);
+
+		/*
+		 * Try again in case a token was freed before we got on the wait
+		 * queue.
+		 */
+		nr = __sbitmap_queue_get(domain_tokens);
+	}
+	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,
+			  bool *flushed)
+{
+	struct list_head *rqs;
+	struct request *rq;
+	int nr;
+
+	rqs = &khd->rqs[khd->cur_domain];
+	rq = list_first_entry_or_null(rqs, struct request, queuelist);
+
+	/*
+	 * If there wasn't already a pending request and we haven't flushed the
+	 * software queues yet, flush the software queues and check again.
+	 */
+	if (!rq && !*flushed) {
+		kyber_flush_busy_ctxs(khd, hctx);
+		*flushed = true;
+		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;
+		}
+	}
+
+	/* 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;
+	bool flushed = false;
+	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, &flushed);
+		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, &flushed);
+		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]))
+			return true;
+	}
+	return false;
+}
+
+#define KYBER_LAT_SHOW_STORE(op)					\
+static ssize_t kyber_##op##_lat_show(struct elevator_queue *e,		\
+				     char *page)			\
+{									\
+	struct kyber_queue_data *kqd = e->elevator_data;		\
+									\
+	return sprintf(page, "%llu\n", kqd->op##_lat_nsec);		\
+}									\
+									\
+static ssize_t kyber_##op##_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->op##_lat_nsec = nsec;					\
+									\
+	return count;							\
+}
+KYBER_LAT_SHOW_STORE(read);
+KYBER_LAT_SHOW_STORE(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
+
+static struct elevator_type kyber_sched = {
+	.ops.mq = {
+		.init_sched = kyber_init_sched,
+		.exit_sched = kyber_exit_sched,
+		.init_hctx = kyber_init_hctx,
+		.exit_hctx = kyber_exit_hctx,
+		.get_request = kyber_get_request,
+		.put_request = kyber_put_request,
+		.completed_request = kyber_completed_request,
+		.dispatch_request = kyber_dispatch_request,
+		.has_work = kyber_has_work,
+	},
+	.uses_mq = true,
+	.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");