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Subject[PATCH v1] block: make the fair sharing of tag configurable
Date
The tags allocation is limited by the fair sharing algorithm. It hurts
the performance for UFS devices, because the queue depth of general I/O
is reduced by half once the UFS send a control command.

Add a new queue flag QUEUE_FLAG_FAIR_TAG_SHARING to make the fair tag
sharing configurable.

See also https://lore.kernel.org/all/20230103195337.158625-1-bvanassche@acm.org

Signed-off-by: Ed Tsai <ed.tsai@mediatek.com>
---
block/blk-mq-debugfs.c | 1 +
block/blk-mq-tag.c | 1 +
block/blk-mq.c | 3 ++-
drivers/ufs/core/ufshcd.c | 3 +++
include/linux/blkdev.h | 6 +++++-
5 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index d23a8554ec4a..f03b8bfe63be 100644
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -103,6 +103,7 @@ static const char *const blk_queue_flag_name[] = {
QUEUE_FLAG_NAME(RQ_ALLOC_TIME),
QUEUE_FLAG_NAME(HCTX_ACTIVE),
QUEUE_FLAG_NAME(NOWAIT),
+ QUEUE_FLAG_NAME(FAIR_TAG_SHARING),
};
#undef QUEUE_FLAG_NAME

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index d6af9d431dc6..b8b36823f5f5 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -97,6 +97,7 @@ static int __blk_mq_get_tag(struct blk_mq_alloc_data *data,
struct sbitmap_queue *bt)
{
if (!data->q->elevator && !(data->flags & BLK_MQ_REQ_RESERVED) &&
+ blk_queue_fair_tag_sharing(data->q) &&
!hctx_may_queue(data->hctx, bt))
return BLK_MQ_NO_TAG;

diff --git a/block/blk-mq.c b/block/blk-mq.c
index f6dad0886a2f..41f7e2b500bd 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1746,7 +1746,8 @@ static bool __blk_mq_alloc_driver_tag(struct request *rq)
bt = &rq->mq_hctx->tags->breserved_tags;
tag_offset = 0;
} else {
- if (!hctx_may_queue(rq->mq_hctx, bt))
+ if (blk_queue_fair_tag_sharing(rq->q) &&
+ !hctx_may_queue(rq->mq_hctx, bt))
return false;
}

diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
index 17d7bb875fee..e96a50265285 100644
--- a/drivers/ufs/core/ufshcd.c
+++ b/drivers/ufs/core/ufshcd.c
@@ -5149,6 +5149,9 @@ static int ufshcd_slave_configure(struct scsi_device *sdev)
blk_queue_update_dma_pad(q, PRDT_DATA_BYTE_COUNT_PAD - 1);
if (hba->quirks & UFSHCD_QUIRK_4KB_DMA_ALIGNMENT)
blk_queue_update_dma_alignment(q, 4096 - 1);
+
+ blk_queue_flag_clear(QUEUE_FLAG_FAIR_TAG_SHARING, q);
+
/*
* Block runtime-pm until all consumers are added.
* Refer ufshcd_setup_links().
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index b441e633f4dd..7fcb2356860d 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -561,10 +561,12 @@ struct request_queue {
#define QUEUE_FLAG_NOWAIT 29 /* device supports NOWAIT */
#define QUEUE_FLAG_SQ_SCHED 30 /* single queue style io dispatch */
#define QUEUE_FLAG_SKIP_TAGSET_QUIESCE 31 /* quiesce_tagset skip the queue*/
+#define QUEUE_FLAG_FAIR_TAG_SHARING 32 /* fair allocation of shared tags */

#define QUEUE_FLAG_MQ_DEFAULT ((1UL << QUEUE_FLAG_IO_STAT) | \
(1UL << QUEUE_FLAG_SAME_COMP) | \
- (1UL << QUEUE_FLAG_NOWAIT))
+ (1UL << QUEUE_FLAG_NOWAIT) | \
+ (1UL << QUEUE_FLAG_FAIR_TAG_SHARING))

void blk_queue_flag_set(unsigned int flag, struct request_queue *q);
void blk_queue_flag_clear(unsigned int flag, struct request_queue *q);
@@ -602,6 +604,8 @@ bool blk_queue_flag_test_and_set(unsigned int flag, struct request_queue *q);
#define blk_queue_sq_sched(q) test_bit(QUEUE_FLAG_SQ_SCHED, &(q)->queue_flags)
#define blk_queue_skip_tagset_quiesce(q) \
test_bit(QUEUE_FLAG_SKIP_TAGSET_QUIESCE, &(q)->queue_flags)
+#define blk_queue_fair_tag_sharing(q) \
+ test_bit(QUEUE_FLAG_FAIR_TAG_SHARING, &(q)->queue_flags)

extern void blk_set_pm_only(struct request_queue *q);
extern void blk_clear_pm_only(struct request_queue *q);
--
2.18.0
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