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Subject[PATCH V2 2/2] block: kyber: make kyber more friendly with merging
Date
Currently, kyber is very unfriendly with merging. kyber depends
on ctx rq_list to do merging, however, most of time, it will not
leave any requests in ctx rq_list. This is because even if tokens
of one domain is used up, kyber will try to dispatch requests
from other domain and flush the rq_list there.

To improve this, we setup kyber_ctx_queue (kcq) which is similar
with ctx, but it has rq_lists for different domain and build same
mapping between kcq and khd as the ctx & hctx. Then we could merge,
insert and dispatch for different domains separately. At the same
time, only flush the rq_list of kcq when get domain token successfully.
Then if one domain token is used up, the requests could be left in
the rq_list of that domain and maybe merged with following io.

Following is my test result on machine with 8 cores and NVMe card
INTEL SSDPEKKR128G7

fio size=256m ioengine=libaio iodepth=64 direct=1 numjobs=8
seq/random
+------+---------------------------------------------------------------+
|patch?| bw(MB/s) | iops | slat(usec) | clat(usec) | merge |
+----------------------------------------------------------------------+
| w/o | 606/612 | 151k/153k | 6.89/7.03 | 3349.21/3305.40 | 0/0 |
+----------------------------------------------------------------------+
| w/ | 1083/616 | 277k/154k | 4.93/6.95 | 1830.62/3279.95 | 223k/3k |
+----------------------------------------------------------------------+
When set numjobs to 16, the bw and iops could reach 1662MB/s and 425k
on my platform.

Signed-off-by: Jianchao Wang <jianchao.w.wang@oracle.com>
Tested-by: Holger Hoffstätte <holger@applied-asynchrony.com>
---
block/kyber-iosched.c | 197 +++++++++++++++++++++++++++++++++++++++++---------
1 file changed, 162 insertions(+), 35 deletions(-)

diff --git a/block/kyber-iosched.c b/block/kyber-iosched.c
index 0d6d25e3..7ca1364 100644
--- a/block/kyber-iosched.c
+++ b/block/kyber-iosched.c
@@ -72,6 +72,15 @@ static const unsigned int kyber_batch_size[] = {
[KYBER_OTHER] = 8,
};

+struct kyber_ctx_queue {
+ /*
+ * Copied from blk_mq_ctx->index_hw
+ */
+ unsigned int index;
+ spinlock_t lock;
+ struct list_head rq_list[KYBER_NUM_DOMAINS];
+} ____cacheline_aligned_in_smp;
+
struct kyber_queue_data {
struct request_queue *q;

@@ -99,6 +108,8 @@ struct kyber_hctx_data {
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];
wait_queue_entry_t domain_wait[KYBER_NUM_DOMAINS];
struct sbq_wait_state *domain_ws[KYBER_NUM_DOMAINS];
atomic_t wait_index[KYBER_NUM_DOMAINS];
@@ -107,10 +118,8 @@ struct kyber_hctx_data {
static int kyber_domain_wake(wait_queue_entry_t *wait, unsigned mode, int flags,
void *key);

-static int rq_sched_domain(const struct request *rq)
+static int kyber_sched_domain(unsigned int op)
{
- 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))
@@ -284,6 +293,11 @@ static unsigned int kyber_sched_tags_shift(struct kyber_queue_data *kqd)
return kqd->q->queue_hw_ctx[0]->sched_tags->bitmap_tags.sb.shift;
}

+static int kyber_bucket_fn(const struct request *rq)
+{
+ return kyber_sched_domain(rq->cmd_flags);
+}
+
static struct kyber_queue_data *kyber_queue_data_alloc(struct request_queue *q)
{
struct kyber_queue_data *kqd;
@@ -297,11 +311,10 @@ static struct kyber_queue_data *kyber_queue_data_alloc(struct request_queue *q)
goto err;
kqd->q = q;

- kqd->cb = blk_stat_alloc_callback(kyber_stat_timer_fn, rq_sched_domain,
+ kqd->cb = blk_stat_alloc_callback(kyber_stat_timer_fn, kyber_bucket_fn,
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
@@ -376,15 +389,45 @@ static void kyber_exit_sched(struct elevator_queue *e)
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_hctx_data *khd;
- int i;
+ int i, sd;

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;
+ /*
+ * clone the mapping between hctx and ctx to khd and kcq
+ */
+ for (i = 0; i < hctx->nr_ctx; i++) {
+ kyber_ctx_queue_init(&khd->kcqs[i]);
+ khd->kcqs[i].index = i;
+ }
+
+ sd = 0;
+ 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))
+ goto err_kcq_map;
+ sd++;
+ }
+
spin_lock_init(&khd->lock);

for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
@@ -402,10 +445,24 @@ static int kyber_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
hctx->sched_data = khd;

return 0;
+
+err_kcq_map:
+ for (i = 0; i < sd; i++)
+ sbitmap_free(&khd->kcq_map[i]);
+ 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);
}

@@ -427,7 +484,7 @@ static void rq_clear_domain_token(struct kyber_queue_data *kqd,

nr = rq_get_domain_token(rq);
if (nr != -1) {
- sched_domain = rq_sched_domain(rq);
+ sched_domain = kyber_sched_domain(rq->cmd_flags);
sbitmap_queue_clear(&kqd->domain_tokens[sched_domain], nr,
rq->mq_ctx->cpu);
}
@@ -446,11 +503,51 @@ static void kyber_limit_depth(unsigned int op, struct blk_mq_alloc_data *data)
}
}

+static bool kyber_bio_merge(struct blk_mq_hw_ctx *hctx, struct bio *bio)
+{
+ 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];
+ struct list_head *rq_list = &kcq->rq_list[kyber_sched_domain(bio->bi_opf)];
+ bool merged;
+
+ spin_lock(&kcq->lock);
+ merged = blk_mq_bio_list_merge(hctx->queue, rq_list, bio);
+ spin_unlock(&kcq->lock);
+ blk_mq_put_ctx(ctx);
+
+ return merged;
+}
+
static void kyber_prepare_request(struct request *rq, struct bio *bio)
{
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 kyber_ctx_queue *kcq;
+ struct request *rq, *next;
+ struct list_head *head;
+ unsigned int sched_domain;
+
+ list_for_each_entry_safe(rq, next, rq_list, queuelist) {
+ sched_domain = kyber_sched_domain(rq->cmd_flags);
+ kcq = &khd->kcqs[rq->mq_ctx->index_hw];
+ 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], kcq->index);
+ 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;
@@ -469,7 +566,7 @@ static void kyber_completed_request(struct request *rq)
* Check if this request met our latency goal. If not, quickly gather
* some statistics and start throttling.
*/
- sched_domain = rq_sched_domain(rq);
+ sched_domain = kyber_sched_domain(rq->cmd_flags);
switch (sched_domain) {
case KYBER_READ:
target = kqd->read_lat_nsec;
@@ -495,19 +592,36 @@ static void kyber_completed_request(struct request *rq)
blk_stat_activate_msecs(kqd->cb, 10);
}

-static void kyber_flush_busy_ctxs(struct kyber_hctx_data *khd,
- struct blk_mq_hw_ctx *hctx)
+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)
{
- LIST_HEAD(rq_list);
- struct request *rq, *next;
+ struct flush_kcq_data *flush_data = data;
+ struct kyber_ctx_queue *kcq = &flush_data->khd->kcqs[bitnr];

- blk_mq_flush_busy_ctxs(hctx, &rq_list);
- list_for_each_entry_safe(rq, next, &rq_list, queuelist) {
- unsigned int sched_domain;
+ 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);

- sched_domain = rq_sched_domain(rq);
- list_move_tail(&rq->queuelist, &khd->rqs[sched_domain]);
- }
+ 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 *wait, unsigned mode, int flags,
@@ -570,26 +684,19 @@ static int kyber_get_domain_token(struct kyber_queue_data *kqd,
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 blk_mq_hw_ctx *hctx)
{
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 we do have cur_domain rqs on khd or kcq list, then try to require
+ * the token
*/
- if (!rq && !*flushed) {
- kyber_flush_busy_ctxs(khd, hctx);
- *flushed = true;
- rq = list_first_entry_or_null(rqs, struct request, queuelist);
- }
-
+ rq = list_first_entry_or_null(rqs, struct request, queuelist);
if (rq) {
nr = kyber_get_domain_token(kqd, khd, hctx);
if (nr >= 0) {
@@ -598,8 +705,25 @@ kyber_dispatch_cur_domain(struct kyber_queue_data *kqd,
list_del_init(&rq->queuelist);
return rq;
}
+ } 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_or_null(rqs, struct request, queuelist);
+ /*
+ * khd->lock and kcq->lock will ensure that, if kcq_map[cur_domain]
+ * is set, we must be able to get requests from the kcq
+ */
+ khd->batching++;
+ rq_set_domain_token(rq, nr);
+ list_del_init(&rq->queuelist);
+ return rq;
+ }
+ /*
+ * if not get domain token, the rqs could be left on kcqs to merged
+ * with following ios.
+ */
}
-
/* There were either no pending requests or no tokens. */
return NULL;
}
@@ -608,7 +732,6 @@ 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;

@@ -619,7 +742,7 @@ static struct request *kyber_dispatch_request(struct blk_mq_hw_ctx *hctx)
* from the batch.
*/
if (khd->batching < kyber_batch_size[khd->cur_domain]) {
- rq = kyber_dispatch_cur_domain(kqd, khd, hctx, &flushed);
+ rq = kyber_dispatch_cur_domain(kqd, khd, hctx);
if (rq)
goto out;
}
@@ -640,7 +763,7 @@ static struct request *kyber_dispatch_request(struct blk_mq_hw_ctx *hctx)
else
khd->cur_domain++;

- rq = kyber_dispatch_cur_domain(kqd, khd, hctx, &flushed);
+ rq = kyber_dispatch_cur_domain(kqd, khd, hctx);
if (rq)
goto out;
}
@@ -657,10 +780,12 @@ static bool kyber_has_work(struct blk_mq_hw_ctx *hctx)
int i;

for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
- if (!list_empty_careful(&khd->rqs[i]))
+ if (!list_empty_careful(&khd->rqs[i]) ||
+ sbitmap_any_bit_set(&khd->kcq_map[i]))
return true;
}
- return sbitmap_any_bit_set(&hctx->ctx_map);
+
+ return false;
}

#define KYBER_LAT_SHOW_STORE(op) \
@@ -831,7 +956,9 @@ static struct elevator_type kyber_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,
--
2.7.4
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