--- /dev/null
+/*
+ * 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");
projects / linux-2.6-microblaze.git / commitdiff