[PATCH 4/8] blk-mq: Facilitate a shared sbitmap per tagset

Hannes Reinecke
2019-11-26T09:14:30Z

From: John Garry <john.garry@huawei.com>

Some SCSI HBAs (such as HPSA, megaraid, mpt3sas, hisi_sas_v3 ..) support
multiple reply queues with single hostwide tags.

In addition, these drivers want to use interrupt assignment in
pci_alloc_irq_vectors(PCI_IRQ_AFFINITY). However, as discussed in [0],
CPU hotplug may cause in-flight IO completion to not be serviced when an
interrupt is shutdown.

To solve that problem, Ming's patchset to drain hctx's should ensure no
IOs are missed in-flight [1].

However, to take advantage of that patchset, we need to map the HBA HW
queues to blk mq hctx's; to do that, we need to expose the HBA HW queues.

In making that transition, the per-SCSI command request tags are no
longer unique per Scsi host - they are just unique per hctx. As such, the
HBA LLDD would have to generate this tag internally, which has a certain
performance overhead.

However another problem is that blk mq assumes the host may accept
(Scsi_host.can_queue * #hw queue) commands. In [2], we removed the Scsi
host busy counter, which would stop the LLDD being sent more than
.can_queue commands; however, we should still ensure that the block layer
does not issue more than .can_queue commands to the Scsi host.

To solve this problem, introduce a shared sbitmap per blk_mq_tag_set,
which may be requested at init time.

New flag BLK_MQ_F_TAG_HCTX_SHARED should be set when requesting the
tagset to indicate whether the shared sbitmap should be used.

Even when BLK_MQ_F_TAG_HCTX_SHARED is set, we still allocate a full set of
tags and requests per hctx; the reason for this is that if we only allocate
tags and requests for a single hctx - like hctx0 - we may break block
drivers which expect a request be associated with a specific hctx, i.e.
not hctx0.

This is based on work originally from Ming Lei in [3] and from Bart's
suggestion in [4].

[0] https://lore.kernel.org/linux-block/alpine.DEB.2.21.1904051331270.1802@nanos.tec.linutronix.de/
[1] https://lore.kernel.org/linux-block/20191014015043.25029-1-ming.lei@redhat.com/
[2] https://lore.kernel.org/linux-scsi/20191025065855.6309-1-ming.lei@redhat.com/
[3] https://lore.kernel.org/linux-block/20190531022801.10003-1-ming.lei@redhat.com/
[4] https://lore.kernel.org/linux-block/ff77beff-5fd9-9f05-12b6-826922bace1f@huawei.com/T/#m3db0a602f095cbcbff27e9c884d6b4ae826144be

Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Hannes Reinecke <hare@suse.de>
---
block/blk-mq-sched.c | 8 ++++++--
block/blk-mq-tag.c | 36 +++++++++++++++++++++++++++++-------
block/blk-mq-tag.h | 6 +++++-
block/blk-mq.c | 45 ++++++++++++++++++++++++++++++++++++---------
block/blk-mq.h | 7 ++++++-
include/linux/blk-mq.h | 7 +++++++
6 files changed, 89 insertions(+), 20 deletions(-)

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index ca22afd47b3d..f3589f42b96d 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -452,7 +452,7 @@ static void blk_mq_sched_free_tags(struct blk_mq_tag_set *set,
{
if (hctx->sched_tags) {
blk_mq_free_rqs(set, hctx->sched_tags, hctx_idx);
- blk_mq_free_rq_map(hctx->sched_tags);
+ blk_mq_free_rq_map(hctx->sched_tags, false);
hctx->sched_tags = NULL;
}
}
@@ -462,10 +462,14 @@ static int blk_mq_sched_alloc_tags(struct request_queue *q,
unsigned int hctx_idx)
{
struct blk_mq_tag_set *set = q->tag_set;
+ int flags = set->flags;
int ret;

+ /* Scheduler tags are never shared */
+ set->flags &= ~BLK_MQ_F_TAG_HCTX_SHARED;
hctx->sched_tags = blk_mq_alloc_rq_map(set, hctx_idx, q->nr_requests,
set->reserved_tags);
+ set->flags = flags;
if (!hctx->sched_tags)
return -ENOMEM;

@@ -484,7 +488,7 @@ static void blk_mq_sched_tags_teardown(struct request_queue *q)

queue_for_each_hw_ctx(q, hctx, i) {
if (hctx->sched_tags) {
- blk_mq_free_rq_map(hctx->sched_tags);
+ blk_mq_free_rq_map(hctx->sched_tags, false);
hctx->sched_tags = NULL;
}
}
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 332d71cd3976..53b4c4c53c6a 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -228,7 +228,7 @@ static bool bt_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data)
* We can hit rq == NULL here, because the tagging functions
* test and set the bit before assigning ->rqs[].
*/
- if (rq && rq->q == hctx->queue)
+ if (rq && rq->q == hctx->queue && rq->mq_hctx == hctx)
return iter_data->fn(hctx, rq, iter_data->data, reserved);
return true;
}
@@ -470,7 +470,27 @@ static int blk_mq_init_bitmap_tags(struct blk_mq_tags *tags,
return -ENOMEM;
}

-struct blk_mq_tags *blk_mq_init_tags(unsigned int total_tags,
+bool blk_mq_init_shared_sbitmap(struct blk_mq_tag_set *tag_set)
+{
+ unsigned int depth = tag_set->queue_depth -tag_set->reserved_tags;
+ int alloc_policy = BLK_MQ_FLAG_TO_ALLOC_POLICY(tag_set->flags);
+ bool round_robin = alloc_policy == BLK_TAG_ALLOC_RR;
+ int node = tag_set->numa_node;
+
+ if (bt_alloc(&tag_set->shared_bitmap_tags, depth, round_robin, node))
+ return false;
+ if (bt_alloc(&tag_set->shared_breserved_tags, tag_set->reserved_tags, round_robin,
+ node))
+ goto free_bitmap_tags;
+
+ return true;
+free_bitmap_tags:
+ sbitmap_queue_free(&tag_set->shared_bitmap_tags);
+ return false;
+}
+
+struct blk_mq_tags *blk_mq_init_tags(struct blk_mq_tag_set *set,
+ unsigned int total_tags,
unsigned int reserved_tags,
int node, int alloc_policy)
{
@@ -488,9 +508,11 @@ struct blk_mq_tags *blk_mq_init_tags(unsigned int total_tags,
tags->nr_tags = total_tags;
tags->nr_reserved_tags = reserved_tags;

- if (blk_mq_init_bitmap_tags(tags, node, alloc_policy) < 0) {
- kfree(tags);
- tags = NULL;
+ if (!blk_mq_is_sbitmap_shared(set)) {
+ if (blk_mq_init_bitmap_tags(tags, node, alloc_policy) < 0) {
+ kfree(tags);
+ tags = NULL;
+ }
}
return tags;
}
@@ -538,12 +560,12 @@ int blk_mq_tag_update_depth(struct blk_mq_hw_ctx *hctx,
return -ENOMEM;
ret = blk_mq_alloc_rqs(set, new, hctx->queue_num, tdepth);
if (ret) {
- blk_mq_free_rq_map(new);
+ blk_mq_free_rq_map(new, blk_mq_is_sbitmap_shared(set));
return -ENOMEM;
}

blk_mq_free_rqs(set, *tagsptr, hctx->queue_num);
- blk_mq_free_rq_map(*tagsptr);
+ blk_mq_free_rq_map(*tagsptr, blk_mq_is_sbitmap_shared(set));
*tagsptr = new;
} else {
/*
diff --git a/block/blk-mq-tag.h b/block/blk-mq-tag.h
index 10b66fd4664a..279a861c7e58 100644
--- a/block/blk-mq-tag.h
+++ b/block/blk-mq-tag.h
@@ -22,7 +22,11 @@ struct blk_mq_tags {
};

-extern struct blk_mq_tags *blk_mq_init_tags(unsigned int nr_tags, unsigned int reserved_tags, int node, int alloc_policy);
+extern bool blk_mq_init_shared_sbitmap(struct blk_mq_tag_set *tag_set);
+extern struct blk_mq_tags *blk_mq_init_tags(struct blk_mq_tag_set *tag_set,
+ unsigned int nr_tags,
+ unsigned int reserved_tags,
+ int node, int alloc_policy);
extern void blk_mq_free_tags(struct blk_mq_tags *tags);

extern unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data);
diff --git a/block/blk-mq.c b/block/blk-mq.c
index f0c40fcbd8ae..db87b0f57dbe 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2075,13 +2075,14 @@ void blk_mq_free_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags,
}
}

-void blk_mq_free_rq_map(struct blk_mq_tags *tags)
+void blk_mq_free_rq_map(struct blk_mq_tags *tags, bool shared)
{
kfree(tags->rqs);
tags->rqs = NULL;
kfree(tags->static_rqs);
tags->static_rqs = NULL;
- blk_mq_free_tags(tags);
+ if (!shared)
+ blk_mq_free_tags(tags);
}

struct blk_mq_tags *blk_mq_alloc_rq_map(struct blk_mq_tag_set *set,
@@ -2096,7 +2097,7 @@ struct blk_mq_tags *blk_mq_alloc_rq_map(struct blk_mq_tag_set *set,
if (node == NUMA_NO_NODE)
node = set->numa_node;

- tags = blk_mq_init_tags(nr_tags, reserved_tags, node,
+ tags = blk_mq_init_tags(set, nr_tags, reserved_tags, node,
BLK_MQ_FLAG_TO_ALLOC_POLICY(set->flags));
if (!tags)
return NULL;
@@ -2105,7 +2106,8 @@ struct blk_mq_tags *blk_mq_alloc_rq_map(struct blk_mq_tag_set *set,
GFP_NOIO | __GFP_NOWARN | __GFP_NORETRY,
node);
if (!tags->rqs) {
- blk_mq_free_tags(tags);
+ if (!blk_mq_is_sbitmap_shared(set))
+ blk_mq_free_tags(tags);
return NULL;
}

@@ -2114,7 +2116,8 @@ struct blk_mq_tags *blk_mq_alloc_rq_map(struct blk_mq_tag_set *set,
node);
if (!tags->static_rqs) {
kfree(tags->rqs);
- blk_mq_free_tags(tags);
+ if (!blk_mq_is_sbitmap_shared(set))
+ blk_mq_free_tags(tags);
return NULL;
}

@@ -2446,7 +2449,7 @@ static bool __blk_mq_alloc_rq_map(struct blk_mq_tag_set *set, int hctx_idx)
if (!ret)
return true;

- blk_mq_free_rq_map(set->tags[hctx_idx]);
+ blk_mq_free_rq_map(set->tags[hctx_idx], blk_mq_is_sbitmap_shared(set));
set->tags[hctx_idx] = NULL;
return false;
}
@@ -2456,7 +2459,8 @@ static void blk_mq_free_map_and_requests(struct blk_mq_tag_set *set,
{
if (set->tags && set->tags[hctx_idx]) {
blk_mq_free_rqs(set, set->tags[hctx_idx], hctx_idx);
- blk_mq_free_rq_map(set->tags[hctx_idx]);
+ blk_mq_free_rq_map(set->tags[hctx_idx],
+ blk_mq_is_sbitmap_shared(set));
set->tags[hctx_idx] = NULL;
}
}
@@ -2954,7 +2958,7 @@ static int __blk_mq_alloc_rq_maps(struct blk_mq_tag_set *set)

out_unwind:
while (--i >= 0)
- blk_mq_free_rq_map(set->tags[i]);
+ blk_mq_free_rq_map(set->tags[i], blk_mq_is_sbitmap_shared(set));

return -ENOMEM;
}
@@ -3099,6 +3103,20 @@ int blk_mq_alloc_tag_set(struct blk_mq_tag_set *set)
if (ret)
goto out_free_mq_map;

+ if (blk_mq_is_sbitmap_shared(set)) {
+ if (!blk_mq_init_shared_sbitmap(set)) {
+ ret = -ENOMEM;
+ goto out_free_mq_map;
+ }
+
+ for (i = 0; i < set->nr_hw_queues; i++) {
+ struct blk_mq_tags *tags = set->tags[i];
+
+ tags->bitmap_tags = &set->shared_bitmap_tags;
+ tags->breserved_tags = &set->shared_breserved_tags;
+ }
+ }
+
mutex_init(&set->tag_list_lock);
INIT_LIST_HEAD(&set->tag_list);

@@ -3168,8 +3186,17 @@ int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)
q->elevator->type->ops.depth_updated(hctx);
}

- if (!ret)
+ if (!ret) {
+ if (blk_mq_is_sbitmap_shared(set)) {
+ sbitmap_queue_resize(&set->shared_bitmap_tags, nr);
+ sbitmap_queue_resize(&set->shared_breserved_tags, nr);
+ }
q->nr_requests = nr;
+ }
+ /*
+ * if ret != 0, q->nr_requests would not be updated, yet the depth
+ * for some hctx may have changed - is that right?
+ */

blk_mq_unquiesce_queue(q);
blk_mq_unfreeze_queue(q);
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 78d38b5f2793..c4b8213dfdfc 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -53,7 +53,7 @@ struct request *blk_mq_dequeue_from_ctx(struct blk_mq_hw_ctx *hctx,
*/
void blk_mq_free_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags,
unsigned int hctx_idx);
-void blk_mq_free_rq_map(struct blk_mq_tags *tags);
+void blk_mq_free_rq_map(struct blk_mq_tags *tags, bool shared);
struct blk_mq_tags *blk_mq_alloc_rq_map(struct blk_mq_tag_set *set,
unsigned int hctx_idx,
unsigned int nr_tags,
@@ -166,6 +166,11 @@ struct blk_mq_alloc_data {
struct blk_mq_hw_ctx *hctx;
};

+static inline bool blk_mq_is_sbitmap_shared(struct blk_mq_tag_set *tag_set)
+{
+ return !!(tag_set->flags & BLK_MQ_F_TAG_HCTX_SHARED);
+}
+
static inline struct blk_mq_tags *blk_mq_tags_from_data(struct blk_mq_alloc_data *data)
{
if (data->flags & BLK_MQ_REQ_INTERNAL)
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 147185394a25..670e9a949d32 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -109,6 +109,12 @@ struct blk_mq_tag_set {
unsigned int flags; /* BLK_MQ_F_* */
void *driver_data;

+ struct sbitmap_queue shared_bitmap_tags;
+ struct sbitmap_queue shared_breserved_tags;
+
+ struct sbitmap_queue sched_shared_bitmap_tags;
+ struct sbitmap_queue sched_shared_breserved_tags;
+
struct blk_mq_tags **tags;

struct mutex tag_list_lock;
@@ -226,6 +232,7 @@ struct blk_mq_ops {
enum {
BLK_MQ_F_SHOULD_MERGE = 1 << 0,
BLK_MQ_F_TAG_QUEUE_SHARED = 1 << 1,
+ BLK_MQ_F_TAG_HCTX_SHARED = 1 << 2,
BLK_MQ_F_BLOCKING = 1 << 5,
BLK_MQ_F_NO_SCHED = 1 << 6,
BLK_MQ_F_ALLOC_POLICY_START_BIT = 8,
--
2.16.4