blk-mq-sched: add framework for MQ capable IO schedulers
This adds a set of hooks that intercepts the blk-mq path of
allocating/inserting/issuing/completing requests, allowing
us to develop a scheduler within that framework.
We reuse the existing elevator scheduler API on the registration
side, but augment that with the scheduler flagging support for
the blk-mq interfce, and with a separate set of ops hooks for MQ
devices.
We split driver and scheduler tags, so we can run the scheduling
independently of device queue depth.
Signed-off-by: Jens Axboe <axboe@fb.com>
Reviewed-by: Bart Van Assche <bart.vanassche@sandisk.com>
Reviewed-by: Omar Sandoval <osandov@fb.com>
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 89b8125..45e1707 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -32,6 +32,7 @@
#include "blk-mq-tag.h"
#include "blk-stat.h"
#include "blk-wbt.h"
+#include "blk-mq-sched.h"
static DEFINE_MUTEX(all_q_mutex);
static LIST_HEAD(all_q_list);
@@ -41,7 +42,9 @@
*/
static bool blk_mq_hctx_has_pending(struct blk_mq_hw_ctx *hctx)
{
- return sbitmap_any_bit_set(&hctx->ctx_map);
+ return sbitmap_any_bit_set(&hctx->ctx_map) ||
+ !list_empty_careful(&hctx->dispatch) ||
+ blk_mq_sched_has_work(hctx);
}
/*
@@ -223,15 +226,23 @@
tag = blk_mq_get_tag(data);
if (tag != BLK_MQ_TAG_FAIL) {
- rq = data->hctx->tags->static_rqs[tag];
+ struct blk_mq_tags *tags = blk_mq_tags_from_data(data);
+
+ rq = tags->static_rqs[tag];
if (blk_mq_tag_busy(data->hctx)) {
rq->rq_flags = RQF_MQ_INFLIGHT;
atomic_inc(&data->hctx->nr_active);
}
- rq->tag = tag;
- data->hctx->tags->rqs[tag] = rq;
+ if (data->flags & BLK_MQ_REQ_INTERNAL) {
+ rq->tag = -1;
+ rq->internal_tag = tag;
+ } else {
+ rq->tag = tag;
+ rq->internal_tag = -1;
+ }
+
blk_mq_rq_ctx_init(data->q, data->ctx, rq, op);
return rq;
}
@@ -243,26 +254,21 @@
struct request *blk_mq_alloc_request(struct request_queue *q, int rw,
unsigned int flags)
{
- struct blk_mq_ctx *ctx;
- struct blk_mq_hw_ctx *hctx;
- struct request *rq;
struct blk_mq_alloc_data alloc_data;
+ struct request *rq;
int ret;
ret = blk_queue_enter(q, flags & BLK_MQ_REQ_NOWAIT);
if (ret)
return ERR_PTR(ret);
- ctx = blk_mq_get_ctx(q);
- hctx = blk_mq_map_queue(q, ctx->cpu);
- blk_mq_set_alloc_data(&alloc_data, q, flags, ctx, hctx);
- rq = __blk_mq_alloc_request(&alloc_data, rw);
- blk_mq_put_ctx(ctx);
+ rq = blk_mq_sched_get_request(q, NULL, rw, &alloc_data);
- if (!rq) {
- blk_queue_exit(q);
+ blk_mq_put_ctx(alloc_data.ctx);
+ blk_queue_exit(q);
+
+ if (!rq)
return ERR_PTR(-EWOULDBLOCK);
- }
rq->__data_len = 0;
rq->__sector = (sector_t) -1;
@@ -322,10 +328,10 @@
}
EXPORT_SYMBOL_GPL(blk_mq_alloc_request_hctx);
-void __blk_mq_free_request(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx,
- struct request *rq)
+void __blk_mq_finish_request(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx,
+ struct request *rq)
{
- const int tag = rq->tag;
+ const int sched_tag = rq->internal_tag;
struct request_queue *q = rq->q;
if (rq->rq_flags & RQF_MQ_INFLIGHT)
@@ -336,22 +342,30 @@
clear_bit(REQ_ATOM_STARTED, &rq->atomic_flags);
clear_bit(REQ_ATOM_POLL_SLEPT, &rq->atomic_flags);
- blk_mq_put_tag(hctx, hctx->tags, ctx, tag);
+ if (rq->tag != -1)
+ blk_mq_put_tag(hctx, hctx->tags, ctx, rq->tag);
+ if (sched_tag != -1)
+ blk_mq_sched_completed_request(hctx, rq);
blk_queue_exit(q);
}
-static void blk_mq_free_hctx_request(struct blk_mq_hw_ctx *hctx,
+static void blk_mq_finish_hctx_request(struct blk_mq_hw_ctx *hctx,
struct request *rq)
{
struct blk_mq_ctx *ctx = rq->mq_ctx;
ctx->rq_completed[rq_is_sync(rq)]++;
- __blk_mq_free_request(hctx, ctx, rq);
+ __blk_mq_finish_request(hctx, ctx, rq);
+}
+
+void blk_mq_finish_request(struct request *rq)
+{
+ blk_mq_finish_hctx_request(blk_mq_map_queue(rq->q, rq->mq_ctx->cpu), rq);
}
void blk_mq_free_request(struct request *rq)
{
- blk_mq_free_hctx_request(blk_mq_map_queue(rq->q, rq->mq_ctx->cpu), rq);
+ blk_mq_sched_put_request(rq);
}
EXPORT_SYMBOL_GPL(blk_mq_free_request);
@@ -469,6 +483,8 @@
{
struct request_queue *q = rq->q;
+ blk_mq_sched_started_request(rq);
+
trace_block_rq_issue(q, rq);
rq->resid_len = blk_rq_bytes(rq);
@@ -517,6 +533,7 @@
trace_block_rq_requeue(q, rq);
wbt_requeue(q->rq_wb, &rq->issue_stat);
+ blk_mq_sched_requeue_request(rq);
if (test_and_clear_bit(REQ_ATOM_STARTED, &rq->atomic_flags)) {
if (q->dma_drain_size && blk_rq_bytes(rq))
@@ -551,13 +568,13 @@
rq->rq_flags &= ~RQF_SOFTBARRIER;
list_del_init(&rq->queuelist);
- blk_mq_insert_request(rq, true, false, false);
+ blk_mq_sched_insert_request(rq, true, false, false);
}
while (!list_empty(&rq_list)) {
rq = list_entry(rq_list.next, struct request, queuelist);
list_del_init(&rq->queuelist);
- blk_mq_insert_request(rq, false, false, false);
+ blk_mq_sched_insert_request(rq, false, false, false);
}
blk_mq_run_hw_queues(q, false);
@@ -765,6 +782,12 @@
continue;
el_ret = blk_try_merge(rq, bio);
+ if (el_ret == ELEVATOR_NO_MERGE)
+ continue;
+
+ if (!blk_mq_sched_allow_merge(q, rq, bio))
+ break;
+
if (el_ret == ELEVATOR_BACK_MERGE) {
if (bio_attempt_back_merge(q, rq, bio)) {
ctx->rq_merged++;
@@ -824,6 +847,59 @@
return min(BLK_MQ_MAX_DISPATCH_ORDER - 1, ilog2(queued) + 1);
}
+static bool blk_mq_get_driver_tag(struct request *rq,
+ struct blk_mq_hw_ctx **hctx, bool wait)
+{
+ struct blk_mq_alloc_data data = {
+ .q = rq->q,
+ .ctx = rq->mq_ctx,
+ .hctx = blk_mq_map_queue(rq->q, rq->mq_ctx->cpu),
+ .flags = wait ? 0 : BLK_MQ_REQ_NOWAIT,
+ };
+
+ if (blk_mq_hctx_stopped(data.hctx))
+ return false;
+
+ if (rq->tag != -1) {
+done:
+ if (hctx)
+ *hctx = data.hctx;
+ return true;
+ }
+
+ rq->tag = blk_mq_get_tag(&data);
+ if (rq->tag >= 0) {
+ data.hctx->tags->rqs[rq->tag] = rq;
+ goto done;
+ }
+
+ return false;
+}
+
+/*
+ * If we fail getting a driver tag because all the driver tags are already
+ * assigned and on the dispatch list, BUT the first entry does not have a
+ * tag, then we could deadlock. For that case, move entries with assigned
+ * driver tags to the front, leaving the set of tagged requests in the
+ * same order, and the untagged set in the same order.
+ */
+static bool reorder_tags_to_front(struct list_head *list)
+{
+ struct request *rq, *tmp, *first = NULL;
+
+ list_for_each_entry_safe_reverse(rq, tmp, list, queuelist) {
+ if (rq == first)
+ break;
+ if (rq->tag != -1) {
+ list_move(&rq->queuelist, list);
+ if (!first)
+ first = rq;
+ }
+ }
+
+ return first != NULL;
+}
+
bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list)
{
struct request_queue *q = hctx->queue;
@@ -846,6 +922,12 @@
struct blk_mq_queue_data bd;
rq = list_first_entry(list, struct request, queuelist);
+ if (!blk_mq_get_driver_tag(rq, &hctx, false)) {
+ if (!queued && reorder_tags_to_front(list))
+ continue;
+ blk_mq_sched_mark_restart(hctx);
+ break;
+ }
list_del_init(&rq->queuelist);
bd.rq = rq;
@@ -899,48 +981,17 @@
* the requests in rq_list might get lost.
*
* blk_mq_run_hw_queue() already checks the STOPPED bit
- **/
- blk_mq_run_hw_queue(hctx, true);
+ *
+ * If RESTART is set, then let completion restart the queue
+ * instead of potentially looping here.
+ */
+ if (!blk_mq_sched_needs_restart(hctx))
+ blk_mq_run_hw_queue(hctx, true);
}
return ret != BLK_MQ_RQ_QUEUE_BUSY;
}
-/*
- * Run this hardware queue, pulling any software queues mapped to it in.
- * Note that this function currently has various problems around ordering
- * of IO. In particular, we'd like FIFO behaviour on handling existing
- * items on the hctx->dispatch list. Ignore that for now.
- */
-static void blk_mq_process_rq_list(struct blk_mq_hw_ctx *hctx)
-{
- LIST_HEAD(rq_list);
- LIST_HEAD(driver_list);
-
- if (unlikely(blk_mq_hctx_stopped(hctx)))
- return;
-
- hctx->run++;
-
- /*
- * Touch any software queue that has pending entries.
- */
- blk_mq_flush_busy_ctxs(hctx, &rq_list);
-
- /*
- * If we have previous entries on our dispatch list, grab them
- * and stuff them at the front for more fair dispatch.
- */
- if (!list_empty_careful(&hctx->dispatch)) {
- spin_lock(&hctx->lock);
- if (!list_empty(&hctx->dispatch))
- list_splice_init(&hctx->dispatch, &rq_list);
- spin_unlock(&hctx->lock);
- }
-
- blk_mq_dispatch_rq_list(hctx, &rq_list);
-}
-
static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
{
int srcu_idx;
@@ -950,11 +1001,11 @@
if (!(hctx->flags & BLK_MQ_F_BLOCKING)) {
rcu_read_lock();
- blk_mq_process_rq_list(hctx);
+ blk_mq_sched_dispatch_requests(hctx);
rcu_read_unlock();
} else {
srcu_idx = srcu_read_lock(&hctx->queue_rq_srcu);
- blk_mq_process_rq_list(hctx);
+ blk_mq_sched_dispatch_requests(hctx);
srcu_read_unlock(&hctx->queue_rq_srcu, srcu_idx);
}
}
@@ -1010,8 +1061,7 @@
int i;
queue_for_each_hw_ctx(q, hctx, i) {
- if ((!blk_mq_hctx_has_pending(hctx) &&
- list_empty_careful(&hctx->dispatch)) ||
+ if (!blk_mq_hctx_has_pending(hctx) ||
blk_mq_hctx_stopped(hctx))
continue;
@@ -1148,32 +1198,10 @@
blk_mq_hctx_mark_pending(hctx, ctx);
}
-void blk_mq_insert_request(struct request *rq, bool at_head, bool run_queue,
- bool async)
-{
- struct blk_mq_ctx *ctx = rq->mq_ctx;
- struct request_queue *q = rq->q;
- struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
-
- spin_lock(&ctx->lock);
- __blk_mq_insert_request(hctx, rq, at_head);
- spin_unlock(&ctx->lock);
-
- if (run_queue)
- blk_mq_run_hw_queue(hctx, async);
-}
-
-static void blk_mq_insert_requests(struct request_queue *q,
- struct blk_mq_ctx *ctx,
- struct list_head *list,
- int depth,
- bool from_schedule)
+void blk_mq_insert_requests(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx,
+ struct list_head *list)
{
- struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
-
- trace_block_unplug(q, depth, !from_schedule);
-
/*
* preemption doesn't flush plug list, so it's possible ctx->cpu is
* offline now
@@ -1189,8 +1217,6 @@
}
blk_mq_hctx_mark_pending(hctx, ctx);
spin_unlock(&ctx->lock);
-
- blk_mq_run_hw_queue(hctx, from_schedule);
}
static int plug_ctx_cmp(void *priv, struct list_head *a, struct list_head *b)
@@ -1226,9 +1252,10 @@
BUG_ON(!rq->q);
if (rq->mq_ctx != this_ctx) {
if (this_ctx) {
- blk_mq_insert_requests(this_q, this_ctx,
- &ctx_list, depth,
- from_schedule);
+ trace_block_unplug(this_q, depth, from_schedule);
+ blk_mq_sched_insert_requests(this_q, this_ctx,
+ &ctx_list,
+ from_schedule);
}
this_ctx = rq->mq_ctx;
@@ -1245,8 +1272,9 @@
* on 'ctx_list'. Do those.
*/
if (this_ctx) {
- blk_mq_insert_requests(this_q, this_ctx, &ctx_list, depth,
- from_schedule);
+ trace_block_unplug(this_q, depth, from_schedule);
+ blk_mq_sched_insert_requests(this_q, this_ctx, &ctx_list,
+ from_schedule);
}
}
@@ -1284,51 +1312,39 @@
}
spin_unlock(&ctx->lock);
- __blk_mq_free_request(hctx, ctx, rq);
+ __blk_mq_finish_request(hctx, ctx, rq);
return true;
}
}
-static struct request *blk_mq_map_request(struct request_queue *q,
- struct bio *bio,
- struct blk_mq_alloc_data *data)
-{
- struct blk_mq_hw_ctx *hctx;
- struct blk_mq_ctx *ctx;
- struct request *rq;
-
- blk_queue_enter_live(q);
- ctx = blk_mq_get_ctx(q);
- hctx = blk_mq_map_queue(q, ctx->cpu);
-
- trace_block_getrq(q, bio, bio->bi_opf);
- blk_mq_set_alloc_data(data, q, 0, ctx, hctx);
- rq = __blk_mq_alloc_request(data, bio->bi_opf);
-
- data->hctx->queued++;
- return rq;
-}
-
static blk_qc_t request_to_qc_t(struct blk_mq_hw_ctx *hctx, struct request *rq)
{
- return blk_tag_to_qc_t(rq->tag, hctx->queue_num, false);
+ if (rq->tag != -1)
+ return blk_tag_to_qc_t(rq->tag, hctx->queue_num, false);
+
+ return blk_tag_to_qc_t(rq->internal_tag, hctx->queue_num, true);
}
static void blk_mq_try_issue_directly(struct request *rq, blk_qc_t *cookie)
{
- int ret;
struct request_queue *q = rq->q;
- struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, rq->mq_ctx->cpu);
struct blk_mq_queue_data bd = {
.rq = rq,
.list = NULL,
.last = 1
};
- blk_qc_t new_cookie = request_to_qc_t(hctx, rq);
+ struct blk_mq_hw_ctx *hctx;
+ blk_qc_t new_cookie;
+ int ret;
- if (blk_mq_hctx_stopped(hctx))
+ if (q->elevator)
goto insert;
+ if (!blk_mq_get_driver_tag(rq, &hctx, false))
+ goto insert;
+
+ new_cookie = request_to_qc_t(hctx, rq);
+
/*
* For OK queue, we are done. For error, kill it. Any other
* error (busy), just add it to our list as we previously
@@ -1350,7 +1366,7 @@
}
insert:
- blk_mq_insert_request(rq, false, true, true);
+ blk_mq_sched_insert_request(rq, false, true, true);
}
/*
@@ -1383,9 +1399,14 @@
blk_attempt_plug_merge(q, bio, &request_count, &same_queue_rq))
return BLK_QC_T_NONE;
+ if (blk_mq_sched_bio_merge(q, bio))
+ return BLK_QC_T_NONE;
+
wb_acct = wbt_wait(q->rq_wb, bio, NULL);
- rq = blk_mq_map_request(q, bio, &data);
+ trace_block_getrq(q, bio, bio->bi_opf);
+
+ rq = blk_mq_sched_get_request(q, bio, bio->bi_opf, &data);
if (unlikely(!rq)) {
__wbt_done(q->rq_wb, wb_acct);
return BLK_QC_T_NONE;
@@ -1397,6 +1418,7 @@
if (unlikely(is_flush_fua)) {
blk_mq_bio_to_request(rq, bio);
+ blk_mq_get_driver_tag(rq, NULL, true);
blk_insert_flush(rq);
goto run_queue;
}
@@ -1447,6 +1469,12 @@
goto done;
}
+ if (q->elevator) {
+ blk_mq_put_ctx(data.ctx);
+ blk_mq_bio_to_request(rq, bio);
+ blk_mq_sched_insert_request(rq, false, true, true);
+ goto done;
+ }
if (!blk_mq_merge_queue_io(data.hctx, data.ctx, rq, bio)) {
/*
* For a SYNC request, send it to the hardware immediately. For
@@ -1492,9 +1520,14 @@
} else
request_count = blk_plug_queued_count(q);
+ if (blk_mq_sched_bio_merge(q, bio))
+ return BLK_QC_T_NONE;
+
wb_acct = wbt_wait(q->rq_wb, bio, NULL);
- rq = blk_mq_map_request(q, bio, &data);
+ trace_block_getrq(q, bio, bio->bi_opf);
+
+ rq = blk_mq_sched_get_request(q, bio, bio->bi_opf, &data);
if (unlikely(!rq)) {
__wbt_done(q->rq_wb, wb_acct);
return BLK_QC_T_NONE;
@@ -1506,6 +1539,7 @@
if (unlikely(is_flush_fua)) {
blk_mq_bio_to_request(rq, bio);
+ blk_mq_get_driver_tag(rq, NULL, true);
blk_insert_flush(rq);
goto run_queue;
}
@@ -1544,6 +1578,12 @@
return cookie;
}
+ if (q->elevator) {
+ blk_mq_put_ctx(data.ctx);
+ blk_mq_bio_to_request(rq, bio);
+ blk_mq_sched_insert_request(rq, false, true, true);
+ goto done;
+ }
if (!blk_mq_merge_queue_io(data.hctx, data.ctx, rq, bio)) {
/*
* For a SYNC request, send it to the hardware immediately. For
@@ -1556,6 +1596,7 @@
}
blk_mq_put_ctx(data.ctx);
+done:
return cookie;
}
@@ -1925,9 +1966,11 @@
static void blk_mq_free_map_and_requests(struct blk_mq_tag_set *set,
unsigned int hctx_idx)
{
- blk_mq_free_rqs(set, set->tags[hctx_idx], hctx_idx);
- blk_mq_free_rq_map(set->tags[hctx_idx]);
- set->tags[hctx_idx] = NULL;
+ if (set->tags[hctx_idx]) {
+ blk_mq_free_rqs(set, set->tags[hctx_idx], hctx_idx);
+ blk_mq_free_rq_map(set->tags[hctx_idx]);
+ set->tags[hctx_idx] = NULL;
+ }
}
static void blk_mq_map_swqueue(struct request_queue *q,
@@ -2084,6 +2127,8 @@
struct blk_mq_hw_ctx *hctx;
unsigned int i;
+ blk_mq_sched_teardown(q);
+
/* hctx kobj stays in hctx */
queue_for_each_hw_ctx(q, hctx, i) {
if (!hctx)
@@ -2504,14 +2549,22 @@
struct blk_mq_hw_ctx *hctx;
int i, ret;
- if (!set || nr > set->queue_depth)
+ if (!set)
return -EINVAL;
ret = 0;
queue_for_each_hw_ctx(q, hctx, i) {
if (!hctx->tags)
continue;
- ret = blk_mq_tag_update_depth(hctx->tags, nr);
+ /*
+ * If we're using an MQ scheduler, just update the scheduler
+ * queue depth. This is similar to what the old code would do.
+ */
+ if (!hctx->sched_tags)
+ ret = blk_mq_tag_update_depth(hctx->tags,
+ min(nr, set->queue_depth));
+ else
+ ret = blk_mq_tag_update_depth(hctx->sched_tags, nr);
if (ret)
break;
}
@@ -2704,7 +2757,10 @@
blk_flush_plug_list(plug, false);
hctx = q->queue_hw_ctx[blk_qc_t_to_queue_num(cookie)];
- rq = blk_mq_tag_to_rq(hctx->tags, blk_qc_t_to_tag(cookie));
+ if (!blk_qc_t_is_internal(cookie))
+ rq = blk_mq_tag_to_rq(hctx->tags, blk_qc_t_to_tag(cookie));
+ else
+ rq = blk_mq_tag_to_rq(hctx->sched_tags, blk_qc_t_to_tag(cookie));
return __blk_mq_poll(hctx, rq);
}