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SubjectRe: [PATCH V2 2/2] block: kyber: make kyber more friendly with merging
On Wed, May 23, 2018 at 02:33:22PM +0800, 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. 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>

Thanks, the per-hctx kqcs make much more sense. This is pretty cool! A
few nitpicks below.

> ---
> 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 {

I'm not crazy about this name, but I can't really think of anything
better, so this will have to do.

> + /*
> + * Copied from blk_mq_ctx->index_hw
> + */
> + unsigned int index;

We can just calculate this as kcq - khd->kcqs in the one place we use
it.

> + 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)

Please make this return an unsigned int since that's what we use for
sched_domain everywhere except the stats bucket function.

> {
> - 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;
> -

Unrelated whitespace change.

> /*
> * 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);

Argument whitespace alignment is still wrong here. I guess you have to
pass --strict to checkpatch.pl to get it to warn about that. Usually I
wouldn't be nitpicky about this but I made sure to keep this file nice
and neat, and we need a v3 anyways :)

> + 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))

Whitespace again.

> + goto err_kcq_map;

In this error case, I'd prefer if we did something similar to
kyber_queue_data_alloc() instead of having this obscurely-named sd
variable:

while (--i >= 0)
sbitmap_free(&khd->kcq_map[i]);
goto err_kcqs;

Where err_kcqs is just the kfree(khd->kcqs).

> + 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)

Whitespace.

> +{
> + 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) {

Please declare the variables which are local to the loop iteration
inside of the loop body. I.e.,

unsigned int sched_domain;
struct kyber_ctx_queue *kcq;
struct list_head *head;

> + 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);

This should just be list_first_entry() if we're so sure that we will
always get a request.

> + /*
> + * 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;
> }

Clever logic in this function :) I think it needs a more complete
explanation rather than the little pieces sprinkled about, how about
this (applied on top of your patch):

diff --git a/block/kyber-iosched.c b/block/kyber-iosched.c
index f60bb4ce1fe6..f4f17527b7be 100644
--- a/block/kyber-iosched.c
+++ b/block/kyber-iosched.c
@@ -696,8 +696,12 @@ kyber_dispatch_cur_domain(struct kyber_queue_data *kqd,
rqs = &khd->rqs[khd->cur_domain];

/*
- * If we do have cur_domain rqs on khd or kcq list, then try to require
- * the token
+ * 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) {
@@ -712,20 +716,12 @@ kyber_dispatch_cur_domain(struct kyber_queue_data *kqd,
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
- */
+ rq = list_first_entry(rqs, struct request, queuelist);
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]))

Whitespace.

> 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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