linux/block/kyber-iosched.c
Jan Kara b6e68ee825 blk-mq: Improve performance of non-mq IO schedulers with multiple HW queues
Currently when non-mq aware IO scheduler (BFQ, mq-deadline) is used for
a queue with multiple HW queues, the performance it rather bad. The
problem is that these IO schedulers use queue-wide locking and their
dispatch function does not respect the hctx it is passed in and returns
any request it finds appropriate. Thus locality of request access is
broken and dispatch from multiple CPUs just contends on IO scheduler
locks. For these IO schedulers there's little point in dispatching from
multiple CPUs. Instead dispatch always only from a single CPU to limit
contention.

Below is a comparison of dbench runs on XFS filesystem where the storage
is a raid card with 64 HW queues and to it attached a single rotating
disk. BFQ is used as IO scheduler:

      clients           MQ                     SQ             MQ-Patched
Amean 1      39.12 (0.00%)       43.29 * -10.67%*       36.09 *   7.74%*
Amean 2     128.58 (0.00%)      101.30 *  21.22%*       96.14 *  25.23%*
Amean 4     577.42 (0.00%)      494.47 *  14.37%*      508.49 *  11.94%*
Amean 8     610.95 (0.00%)      363.86 *  40.44%*      362.12 *  40.73%*
Amean 16    391.78 (0.00%)      261.49 *  33.25%*      282.94 *  27.78%*
Amean 32    324.64 (0.00%)      267.71 *  17.54%*      233.00 *  28.23%*
Amean 64    295.04 (0.00%)      253.02 *  14.24%*      242.37 *  17.85%*
Amean 512 10281.61 (0.00%)    10211.16 *   0.69%*    10447.53 *  -1.61%*

Numbers are times so lower is better. MQ is stock 5.10-rc6 kernel. SQ is
the same kernel with megaraid_sas.host_tagset_enable=0 so that the card
advertises just a single HW queue. MQ-Patched is a kernel with this
patch applied.

You can see multiple hardware queues heavily hurt performance in
combination with BFQ. The patch restores the performance.

Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2021-01-24 18:19:46 -07:00

1052 lines
28 KiB
C

// 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 blk_mq_hw_ctx *hctx, struct bio *bio,
unsigned int nr_segs)
{
struct kyber_hctx_data *khd = hctx->sched_data;
struct blk_mq_ctx *ctx = blk_mq_get_ctx(hctx->queue);
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_features = ELEVATOR_F_MQ_AWARE,
.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");