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SubjectRe: [PATCH] block: kyber: make kyber more friendly with merging
From
Date
On 5/22/18 10:20 AM, Jens Axboe wrote:
> On 5/22/18 10:17 AM, Holger Hoffstätte wrote:
>> On 05/22/18 16:48, Jianchao Wang wrote:
>>> 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. 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>
>>
>> <snip>
>>
>> This looks great but prevents kyber from being built as module,
>> which is AFAIK supposed to work (and works now):
>>
>> ..
>> CC [M] block/kyber-iosched.o
>> Building modules, stage 2.
>> MODPOST 313 modules
>> ERROR: "bio_attempt_back_merge" [block/kyber-iosched.ko] undefined!
>> ERROR: "bio_attempt_front_merge" [block/kyber-iosched.ko] undefined!
>> ERROR: "bio_attempt_discard_merge" [block/kyber-iosched.ko] undefined!
>> ERROR: "blk_try_merge" [block/kyber-iosched.ko] undefined!
>> ERROR: "blk_rq_merge_ok" [block/kyber-iosched.ko] undefined!
>> ..
>>
>> It does build fine when compiled in, obviously. :)
>
> It's basically duplicating the contents of blk_attempt_plug_merge().
> I would suggest abstracting out the list loop and merge check
> into a helper, that could then both be called from kyber and the
> plug merge function.

See attached, prep patch and yours rebased on top of it.

--
Jens Axboe

From edb57af07cf619f27a3fee85705870875f853f58 Mon Sep 17 00:00:00 2001
From: Jianchao Wang <jianchao.w.wang@oracle.com>
Date: Tue, 22 May 2018 11:45:01 -0600
Subject: [PATCH 2/2] block: kyber: make kyber more friendly with merging

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. 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>
---
block/kyber-iosched.c | 212 +++++++++++++++++++++++++++++++++++++++++++-------
1 file changed, 184 insertions(+), 28 deletions(-)

diff --git a/block/kyber-iosched.c b/block/kyber-iosched.c
index 5b33dc394cc7..f28147be729b 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;

@@ -84,6 +93,7 @@ struct kyber_queue_data {
*/
struct sbitmap_queue domain_tokens[KYBER_NUM_DOMAINS];

+ struct kyber_ctx_queue *ctx_queue;
/*
* Async request percentage, converted to per-word depth for
* sbitmap_get_shallow().
@@ -99,6 +109,8 @@ 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];
@@ -284,6 +296,19 @@ 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 void kyber_ctx_queue_init(struct kyber_queue_data *kqd)
+{
+ unsigned int i, j;
+
+ for (i = 0; i < nr_cpu_ids; i++) {
+ struct kyber_ctx_queue *kcq = &kqd->ctx_queue[i];
+
+ spin_lock_init(&kcq->lock);
+ for (j = 0; j < KYBER_NUM_DOMAINS; j++)
+ INIT_LIST_HEAD(&kcq->rq_list[j]);
+ }
+}
+
static struct kyber_queue_data *kyber_queue_data_alloc(struct request_queue *q)
{
struct kyber_queue_data *kqd;
@@ -302,6 +327,13 @@ static struct kyber_queue_data *kyber_queue_data_alloc(struct request_queue *q)
if (!kqd->cb)
goto err_kqd;

+ kqd->ctx_queue = kmalloc_array_node(nr_cpu_ids,
+ sizeof(struct kyber_ctx_queue), GFP_KERNEL, -1);
+ if (!kqd->ctx_queue)
+ goto err_cb;
+
+ kyber_ctx_queue_init(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
@@ -318,7 +350,7 @@ static struct kyber_queue_data *kyber_queue_data_alloc(struct request_queue *q)
if (ret) {
while (--i >= 0)
sbitmap_queue_free(&kqd->domain_tokens[i]);
- goto err_cb;
+ goto err_kcq;
}
sbitmap_queue_resize(&kqd->domain_tokens[i], kyber_depth[i]);
}
@@ -331,6 +363,8 @@ static struct kyber_queue_data *kyber_queue_data_alloc(struct request_queue *q)

return kqd;

+err_kcq:
+ kfree(kqd->ctx_queue);
err_cb:
blk_stat_free_callback(kqd->cb);
err_kqd:
@@ -372,6 +406,7 @@ static void kyber_exit_sched(struct elevator_queue *e)

for (i = 0; i < KYBER_NUM_DOMAINS; i++)
sbitmap_queue_free(&kqd->domain_tokens[i]);
+ kfree(kqd->ctx_queue);
blk_stat_free_callback(kqd->cb);
kfree(kqd);
}
@@ -381,11 +416,31 @@ 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;
+ int sd;

khd = kmalloc_node(sizeof(*khd), GFP_KERNEL, hctx->numa_node);
if (!khd)
return -ENOMEM;

+ khd->kcqs = kmalloc_array_node(nr_cpu_ids, sizeof(void *),
+ GFP_KERNEL, hctx->numa_node);
+ if (!khd->kcqs)
+ goto err_khd;
+
+ 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++;
+ }
+ /*
+ * clone the mapping between hctx and ctx to khd and kcq
+ */
+ for (i = 0; i < hctx->nr_ctx; i++) {
+ khd->kcqs[i] = &kqd->ctx_queue[hctx->ctxs[i]->cpu];
+ khd->kcqs[i]->index = i;
+ }
spin_lock_init(&khd->lock);

for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
@@ -405,10 +460,24 @@ static int kyber_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
kqd->async_depth);

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);
}

@@ -449,11 +518,68 @@ static void kyber_limit_depth(unsigned int op, struct blk_mq_alloc_data *data)
}
}

+static int bio_sched_domain(const struct bio *bio)
+{
+ unsigned int op = bio->bi_opf;
+
+ 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;
+}
+
+/*
+ * Do limited merge trying here. Align with blk_mq_attempt_merge, reverse
+ * checking corresponding domain queue for 8 reqs.
+ */
+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[bio_sched_domain(bio)];
+ 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 = rq_sched_domain(rq);
+ 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;
@@ -498,19 +624,36 @@ 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,
@@ -573,26 +716,19 @@ 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) {
@@ -601,8 +737,25 @@ 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;
}
@@ -611,7 +764,6 @@ 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;

@@ -622,7 +774,7 @@ 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;
}
@@ -643,7 +795,7 @@ 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;
}
@@ -660,10 +812,12 @@ 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) \
@@ -834,7 +988,9 @@ 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
From 82d8018412c12407fbfb134c7be5410ba5a76084 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Tue, 22 May 2018 11:41:46 -0600
Subject: [PATCH 1/2] blk-mq: abstract out blk-mq-sched rq list iteration bio
merge helper

No functional changes in this patch, just a prep patch for utilizing
this in an IO scheduler.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
block/blk-mq-sched.c | 34 ++++++++++++++++++++++++----------
include/linux/blk-mq.h | 3 ++-
2 files changed, 26 insertions(+), 11 deletions(-)

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index 25c14c58385c..b0f2c2a40a0c 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -268,19 +268,16 @@ bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,
EXPORT_SYMBOL_GPL(blk_mq_sched_try_merge);

/*
- * Reverse check our software queue for entries that we could potentially
- * merge with. Currently includes a hand-wavy stop count of 8, to not spend
- * too much time checking for merges.
+ * Iterate list of requests and see if we can merge this bio with any
+ * of them.
*/
-static bool blk_mq_attempt_merge(struct request_queue *q,
- struct blk_mq_ctx *ctx, struct bio *bio)
+bool blk_mq_bio_list_merge(struct request_queue *q, struct list_head *list,
+ struct bio *bio)
{
struct request *rq;
int checked = 8;

- lockdep_assert_held(&ctx->lock);
-
- list_for_each_entry_reverse(rq, &ctx->rq_list, queuelist) {
+ list_for_each_entry_reverse(rq, list, queuelist) {
bool merged = false;

if (!checked--)
@@ -305,13 +302,30 @@ static bool blk_mq_attempt_merge(struct request_queue *q,
continue;
}

- if (merged)
- ctx->rq_merged++;
return merged;
}

return false;
}
+EXPORT_SYMBOL_GPL(blk_mq_bio_list_merge);
+
+/*
+ * Reverse check our software queue for entries that we could potentially
+ * merge with. Currently includes a hand-wavy stop count of 8, to not spend
+ * too much time checking for merges.
+ */
+static bool blk_mq_attempt_merge(struct request_queue *q,
+ struct blk_mq_ctx *ctx, struct bio *bio)
+{
+ lockdep_assert_held(&ctx->lock);
+
+ if (blk_mq_bio_list_merge(q, &ctx->rq_list, bio)) {
+ ctx->rq_merged++;
+ return true;
+ }
+
+ return false;
+}

bool __blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio)
{
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index ebc34a5686dc..fb355173f3c7 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -259,7 +259,8 @@ void blk_mq_add_to_requeue_list(struct request *rq, bool at_head,
void blk_mq_kick_requeue_list(struct request_queue *q);
void blk_mq_delay_kick_requeue_list(struct request_queue *q, unsigned long msecs);
void blk_mq_complete_request(struct request *rq);
-
+bool blk_mq_bio_list_merge(struct request_queue *q, struct list_head *list,
+ struct bio *bio);
bool blk_mq_queue_stopped(struct request_queue *q);
void blk_mq_stop_hw_queue(struct blk_mq_hw_ctx *hctx);
void blk_mq_start_hw_queue(struct blk_mq_hw_ctx *hctx);
--
2.7.4
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