diff options
Diffstat (limited to 'block/kyber-iosched.c')
| -rw-r--r-- | block/kyber-iosched.c | 719 |
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..3b0090bc5dd1 --- /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 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"); |