Hi Kashyap,
I have to add additional changes on top of your below patch -
active_queues also should be managed differently for shared tag map case. I
added extra flags in queue_flags interface which is per request.
ok, so it's not proper to use active hctx per request queue as "users",
but rather that the active request_queue's per host (which is what we
effectively have for nr_hw_queues = 1). Just a small comment at the
bottom on your change.
So I already experimented with reducing shost.can_queue significantly on
hisi_sas (by a factor of 8, from 4096->512, and I use 12x SAS SSD), and saw:
RFC + shost.can_queue reduced: ~1.2M IOPS
With RFC + shost.can_queue unmodified: ~2M IOPS
Without RFC + shost.can_queue unmodified: ~2M IOPS
And with the change, below, I still get around 1.2M IOPS. But there may
be some sweet spot/zone where this makes a difference, which I'm not
visiting.
Combination of your patch and below resolves fairness issues. I see some
better results using " --cpus_allowed_policy=split", but
--cpus_allowed_policy=shared
I did not try changing the cpus_allowed_policy policy, and so I would be
using default, which I believe is shared.
is still having some issue and most likely it
is to do with fairness. If fairness is not managed properly, there is high
contention in wait/wakeup handling of sbitmap.
ok, I can investigate.
=====Additional patch ===
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 3719e1a..95bcb47 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -23,10 +23,20 @@
*/
bool __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
{
- if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state) &&
- !test_and_set_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
- atomic_inc(&hctx->tags->active_queues);
+ struct blk_mq_tags *tags = hctx->tags;
+ struct request_queue *q = hctx->queue;
+ struct sbitmap_queue *bt;
+ if (blk_mq_is_sbitmap_shared(q->tag_set)){
+ bt = tags->bitmap_tags;
+ if (!test_bit(QUEUE_FLAG_HCTX_ACTIVE, &q->queue_flags) &&
+ !test_and_set_bit(QUEUE_FLAG_HCTX_ACTIVE,
&q->queue_flags))
+ atomic_inc(&bt->active_queues_per_host);
+ } else {
+ if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state) &&
+ !test_and_set_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
+ atomic_inc(&hctx->tags->active_queues);
+ }
return true;
}
@@ -47,12 +57,20 @@ void blk_mq_tag_wakeup_all(struct blk_mq_tags *tags,
bool include_reserve)
void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
{
struct blk_mq_tags *tags = hctx->tags;
+ struct sbitmap_queue *bt;
+ struct request_queue *q = hctx->queue;
- if (!test_and_clear_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
- return;
-
- atomic_dec(&tags->active_queues);
+ if (blk_mq_is_sbitmap_shared(q->tag_set)){
+ bt = tags->bitmap_tags;
+ if (!test_and_clear_bit(QUEUE_FLAG_HCTX_ACTIVE,
&q->queue_flags))
+ return;
+ atomic_dec(&bt->active_queues_per_host);
+ } else {
+ if (!test_and_clear_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
+ return;
+ atomic_dec(&tags->active_queues);
+ }
blk_mq_tag_wakeup_all(tags, false);
}
@@ -65,12 +83,13 @@ static inline bool hctx_may_queue(struct
blk_mq_alloc_data *data,
{
struct blk_mq_hw_ctx *hctx = data->hctx;
struct request_queue *q = data->q;
+ struct blk_mq_tags *tags = hctx->tags;
unsigned int depth, users;
if (!hctx || !(hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED))
return true;
- if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
- return true;
+ //if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
+ // return true;
/*
* Don't try dividing an ant
@@ -78,7 +97,11 @@ static inline bool hctx_may_queue(struct
blk_mq_alloc_data *data,
if (bt->sb.depth == 1)
return true;
- users = atomic_read(&hctx->tags->active_queues);
+ if (blk_mq_is_sbitmap_shared(q->tag_set)) {
+ bt = tags->bitmap_tags;
+ users = atomic_read(&bt->active_queues_per_host);
+ } else
+ users = atomic_read(&hctx->tags->active_queues);
if (!users)
return true;
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 2bc9998..7049800 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -613,6 +613,7 @@ struct request_queue {
#define QUEUE_FLAG_PCI_P2PDMA 25 /* device supports PCI p2p requests
*/
#define QUEUE_FLAG_ZONE_RESETALL 26 /* supports Zone Reset All */
#define QUEUE_FLAG_RQ_ALLOC_TIME 27 /* record rq->alloc_time_ns */
+#define QUEUE_FLAG_HCTX_ACTIVE 28 /* atleast one hctx is active*/
#define QUEUE_FLAG_MQ_DEFAULT ((1 << QUEUE_FLAG_IO_STAT) | \
(1 << QUEUE_FLAG_SAME_COMP))
diff --git a/include/linux/sbitmap.h b/include/linux/sbitmap.h
index e40d019..fb44925 100644
--- a/include/linux/sbitmap.h
+++ b/include/linux/sbitmap.h
@@ -139,6 +139,8 @@ struct sbitmap_queue {
* sbitmap_queue_get_shallow() or __sbitmap_queue_get_shallow().
*/
unsigned int min_shallow_depth;
+
+ atomic_t active_queues_per_host;
It's prob better to put this in blk_mq_tag_set structure.
};
Thanks very much,
John
