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. 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>
Reviewed-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/kyber-iosched.c b/block/kyber-iosched.c
index 5b33dc394cc7540269f6e69d5e115f05289e495e..a1660bafc912452a37730ac0ed2bf02f6c8a99bc 100644 (file)
--- a/block/kyber-iosched.c
+++ b/block/kyber-iosched.c
@@ -72,6 +72,19 @@ static const unsigned int kyber_batch_size[] = {
        [KYBER_OTHER] = 8,
 };
 
+/*
+ * 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;
 
@@ -99,6 +112,8 @@ 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 +122,8 @@ 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 unsigned 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 +297,11 @@ 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;
@@ -297,7 +315,7 @@ 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;
@@ -376,6 +394,15 @@ 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_queue_data *kqd = hctx->queue->elevator->elevator_data;
@@ -386,6 +413,24 @@ static int kyber_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
        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++) {
@@ -405,10 +450,22 @@ static int kyber_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
                                        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);
 }
 
@@ -430,7 +487,7 @@ 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);
        }
@@ -449,11 +506,51 @@ 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];
+       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_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 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];
+               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);
+               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;
@@ -472,7 +569,7 @@ 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;
@@ -498,19 +595,38 @@ 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 +689,23 @@ 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 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.
         */
-       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) {
@@ -601,6 +714,16 @@ 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(rqs, struct request, queuelist);
+                       khd->batching++;
+                       rq_set_domain_token(rq, nr);
+                       list_del_init(&rq->queuelist);
+                       return rq;
+               }
        }
 
        /* There were either no pending requests or no tokens. */
@@ -611,7 +734,6 @@ 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 +744,7 @@ 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 +765,7 @@ 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 +782,12 @@ 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 +958,9 @@ 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,