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blk-mq: add tag allocation policy
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This is the blk-mq part to support tag allocation policy. The default
allocation policy isn't changed (though it's not a strict FIFO). The new
policy is round-robin for libata. But it's a try-best implementation. If
multiple tasks are competing, the tags returned will be mixed (which is
unavoidable even with !mq, as requests from different tasks can be
mixed in queue)

Cc: Jens Axboe <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Signed-off-by: Shaohua Li <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
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@shligit @axboe
shligit authored and axboe committed Jan 23, 2015
1 parent ee1b6f7 commit 24391c0
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Showing 5 changed files with 39 additions and 17 deletions.
39 changes: 24 additions & 15 deletions block/blk-mq-tag.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -140,7 +140,8 @@ static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx,
return atomic_read(&hctx->nr_active) < depth;
}

static int __bt_get_word(struct blk_align_bitmap *bm, unsigned int last_tag)
static int __bt_get_word(struct blk_align_bitmap *bm, unsigned int last_tag,
bool nowrap)
{
int tag, org_last_tag = last_tag;

Expand All @@ -152,7 +153,7 @@ static int __bt_get_word(struct blk_align_bitmap *bm, unsigned int last_tag)
* offset to 0 in a failure case, so start from 0 to
* exhaust the map.
*/
if (org_last_tag && last_tag) {
if (org_last_tag && last_tag && !nowrap) {
last_tag = org_last_tag = 0;
continue;
}
Expand All @@ -170,6 +171,8 @@ static int __bt_get_word(struct blk_align_bitmap *bm, unsigned int last_tag)
return tag;
}

#define BT_ALLOC_RR(tags) (tags->alloc_policy == BLK_TAG_ALLOC_RR)

/*
* Straight forward bitmap tag implementation, where each bit is a tag
* (cleared == free, and set == busy). The small twist is using per-cpu
Expand All @@ -182,7 +185,7 @@ static int __bt_get_word(struct blk_align_bitmap *bm, unsigned int last_tag)
* until the map is exhausted.
*/
static int __bt_get(struct blk_mq_hw_ctx *hctx, struct blk_mq_bitmap_tags *bt,
unsigned int *tag_cache)
unsigned int *tag_cache, struct blk_mq_tags *tags)
{
unsigned int last_tag, org_last_tag;
int index, i, tag;
Expand All @@ -194,7 +197,8 @@ static int __bt_get(struct blk_mq_hw_ctx *hctx, struct blk_mq_bitmap_tags *bt,
index = TAG_TO_INDEX(bt, last_tag);

for (i = 0; i < bt->map_nr; i++) {
tag = __bt_get_word(&bt->map[index], TAG_TO_BIT(bt, last_tag));
tag = __bt_get_word(&bt->map[index], TAG_TO_BIT(bt, last_tag),
BT_ALLOC_RR(tags));
if (tag != -1) {
tag += (index << bt->bits_per_word);
goto done;
Expand All @@ -221,7 +225,7 @@ static int __bt_get(struct blk_mq_hw_ctx *hctx, struct blk_mq_bitmap_tags *bt,
* up using the specific cached tag.
*/
done:
if (tag == org_last_tag) {
if (tag == org_last_tag || unlikely(BT_ALLOC_RR(tags))) {
last_tag = tag + 1;
if (last_tag >= bt->depth - 1)
last_tag = 0;
Expand Down Expand Up @@ -250,13 +254,13 @@ static struct bt_wait_state *bt_wait_ptr(struct blk_mq_bitmap_tags *bt,
static int bt_get(struct blk_mq_alloc_data *data,
struct blk_mq_bitmap_tags *bt,
struct blk_mq_hw_ctx *hctx,
unsigned int *last_tag)
unsigned int *last_tag, struct blk_mq_tags *tags)
{
struct bt_wait_state *bs;
DEFINE_WAIT(wait);
int tag;

tag = __bt_get(hctx, bt, last_tag);
tag = __bt_get(hctx, bt, last_tag, tags);
if (tag != -1)
return tag;

Expand All @@ -267,7 +271,7 @@ static int bt_get(struct blk_mq_alloc_data *data,
do {
prepare_to_wait(&bs->wait, &wait, TASK_UNINTERRUPTIBLE);

tag = __bt_get(hctx, bt, last_tag);
tag = __bt_get(hctx, bt, last_tag, tags);
if (tag != -1)
break;

Expand All @@ -282,7 +286,7 @@ static int bt_get(struct blk_mq_alloc_data *data,
* Retry tag allocation after running the hardware queue,
* as running the queue may also have found completions.
*/
tag = __bt_get(hctx, bt, last_tag);
tag = __bt_get(hctx, bt, last_tag, tags);
if (tag != -1)
break;

Expand Down Expand Up @@ -313,7 +317,7 @@ static unsigned int __blk_mq_get_tag(struct blk_mq_alloc_data *data)
int tag;

tag = bt_get(data, &data->hctx->tags->bitmap_tags, data->hctx,
&data->ctx->last_tag);
&data->ctx->last_tag, data->hctx->tags);
if (tag >= 0)
return tag + data->hctx->tags->nr_reserved_tags;

Expand All @@ -329,7 +333,8 @@ static unsigned int __blk_mq_get_reserved_tag(struct blk_mq_alloc_data *data)
return BLK_MQ_TAG_FAIL;
}

tag = bt_get(data, &data->hctx->tags->breserved_tags, NULL, &zero);
tag = bt_get(data, &data->hctx->tags->breserved_tags, NULL, &zero,
data->hctx->tags);
if (tag < 0)
return BLK_MQ_TAG_FAIL;

Expand Down Expand Up @@ -401,7 +406,8 @@ void blk_mq_put_tag(struct blk_mq_hw_ctx *hctx, unsigned int tag,

BUG_ON(real_tag >= tags->nr_tags);
bt_clear_tag(&tags->bitmap_tags, real_tag);
*last_tag = real_tag;
if (likely(tags->alloc_policy == BLK_TAG_ALLOC_FIFO))
*last_tag = real_tag;
} else {
BUG_ON(tag >= tags->nr_reserved_tags);
bt_clear_tag(&tags->breserved_tags, tag);
Expand Down Expand Up @@ -538,10 +544,12 @@ static void bt_free(struct blk_mq_bitmap_tags *bt)
}

static struct blk_mq_tags *blk_mq_init_bitmap_tags(struct blk_mq_tags *tags,
int node)
int node, int alloc_policy)
{
unsigned int depth = tags->nr_tags - tags->nr_reserved_tags;

tags->alloc_policy = alloc_policy;

if (bt_alloc(&tags->bitmap_tags, depth, node, false))
goto enomem;
if (bt_alloc(&tags->breserved_tags, tags->nr_reserved_tags, node, true))
Expand All @@ -555,7 +563,8 @@ static struct blk_mq_tags *blk_mq_init_bitmap_tags(struct blk_mq_tags *tags,
}

struct blk_mq_tags *blk_mq_init_tags(unsigned int total_tags,
unsigned int reserved_tags, int node)
unsigned int reserved_tags,
int node, int alloc_policy)
{
struct blk_mq_tags *tags;

Expand All @@ -571,7 +580,7 @@ struct blk_mq_tags *blk_mq_init_tags(unsigned int total_tags,
tags->nr_tags = total_tags;
tags->nr_reserved_tags = reserved_tags;

return blk_mq_init_bitmap_tags(tags, node);
return blk_mq_init_bitmap_tags(tags, node, alloc_policy);
}

void blk_mq_free_tags(struct blk_mq_tags *tags)
Expand Down
4 changes: 3 additions & 1 deletion block/blk-mq-tag.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -42,10 +42,12 @@ struct blk_mq_tags {

struct request **rqs;
struct list_head page_list;

int alloc_policy;
};


extern struct blk_mq_tags *blk_mq_init_tags(unsigned int nr_tags, unsigned int reserved_tags, int node);
extern struct blk_mq_tags *blk_mq_init_tags(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);
Expand Down
3 changes: 2 additions & 1 deletion block/blk-mq.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1374,7 +1374,8 @@ static struct blk_mq_tags *blk_mq_init_rq_map(struct blk_mq_tag_set *set,
size_t rq_size, left;

tags = blk_mq_init_tags(set->queue_depth, set->reserved_tags,
set->numa_node);
set->numa_node,
BLK_MQ_FLAG_TO_ALLOC_POLICY(set->flags));
if (!tags)
return NULL;

Expand Down
2 changes: 2 additions & 0 deletions drivers/scsi/scsi_lib.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2188,6 +2188,8 @@ int scsi_mq_setup_tags(struct Scsi_Host *shost)
shost->tag_set.cmd_size = cmd_size;
shost->tag_set.numa_node = NUMA_NO_NODE;
shost->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_SG_MERGE;
shost->tag_set.flags |=
BLK_ALLOC_POLICY_TO_MQ_FLAG(shost->hostt->tag_alloc_policy);
shost->tag_set.driver_data = shost;

return blk_mq_alloc_tag_set(&shost->tag_set);
Expand Down
8 changes: 8 additions & 0 deletions include/linux/blk-mq.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -147,6 +147,8 @@ enum {
BLK_MQ_F_SG_MERGE = 1 << 2,
BLK_MQ_F_SYSFS_UP = 1 << 3,
BLK_MQ_F_DEFER_ISSUE = 1 << 4,
BLK_MQ_F_ALLOC_POLICY_START_BIT = 8,
BLK_MQ_F_ALLOC_POLICY_BITS = 1,

BLK_MQ_S_STOPPED = 0,
BLK_MQ_S_TAG_ACTIVE = 1,
Expand All @@ -155,6 +157,12 @@ enum {

BLK_MQ_CPU_WORK_BATCH = 8,
};
#define BLK_MQ_FLAG_TO_ALLOC_POLICY(flags) \
((flags >> BLK_MQ_F_ALLOC_POLICY_START_BIT) & \
((1 << BLK_MQ_F_ALLOC_POLICY_BITS) - 1))
#define BLK_ALLOC_POLICY_TO_MQ_FLAG(policy) \
((policy & ((1 << BLK_MQ_F_ALLOC_POLICY_BITS) - 1)) \
<< BLK_MQ_F_ALLOC_POLICY_START_BIT)

struct request_queue *blk_mq_init_queue(struct blk_mq_tag_set *);
void blk_mq_finish_init(struct request_queue *q);
Expand Down

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