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null_blk: add support for shared tags
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Some storage drivers need to share tag sets between devices. It's
useful to be able to model that with null_blk, to find hangs or
performance issues.

Add a 'shared_tags' bool module parameter that. If that is set to
true and nr_devices is bigger than 1, all devices allocated will
share the same tag set.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
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Jens Axboe committed Jun 20, 2017
1 parent edf064e commit 82f402f
Showing 1 changed file with 70 additions and 42 deletions.
112 changes: 70 additions & 42 deletions drivers/block/null_blk.c
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Original file line number Diff line number Diff line change
Expand Up @@ -35,7 +35,8 @@ struct nullb {
struct request_queue *q;
struct gendisk *disk;
struct nvm_dev *ndev;
struct blk_mq_tag_set tag_set;
struct blk_mq_tag_set *tag_set;
struct blk_mq_tag_set __tag_set;
struct hrtimer timer;
unsigned int queue_depth;
spinlock_t lock;
Expand All @@ -50,6 +51,7 @@ static struct mutex lock;
static int null_major;
static int nullb_indexes;
static struct kmem_cache *ppa_cache;
static struct blk_mq_tag_set tag_set;

enum {
NULL_IRQ_NONE = 0,
Expand Down Expand Up @@ -109,7 +111,7 @@ static int bs = 512;
module_param(bs, int, S_IRUGO);
MODULE_PARM_DESC(bs, "Block size (in bytes)");

static int nr_devices = 2;
static int nr_devices = 1;
module_param(nr_devices, int, S_IRUGO);
MODULE_PARM_DESC(nr_devices, "Number of devices to register");

Expand All @@ -121,6 +123,10 @@ static bool blocking;
module_param(blocking, bool, S_IRUGO);
MODULE_PARM_DESC(blocking, "Register as a blocking blk-mq driver device");

static bool shared_tags;
module_param(shared_tags, bool, S_IRUGO);
MODULE_PARM_DESC(shared_tags, "Share tag set between devices for blk-mq");

static int irqmode = NULL_IRQ_SOFTIRQ;

static int null_set_irqmode(const char *str, const struct kernel_param *kp)
Expand Down Expand Up @@ -376,31 +382,8 @@ static blk_status_t null_queue_rq(struct blk_mq_hw_ctx *hctx,
return BLK_STS_OK;
}

static void null_init_queue(struct nullb *nullb, struct nullb_queue *nq)
{
BUG_ON(!nullb);
BUG_ON(!nq);

init_waitqueue_head(&nq->wait);
nq->queue_depth = nullb->queue_depth;
}

static int null_init_hctx(struct blk_mq_hw_ctx *hctx, void *data,
unsigned int index)
{
struct nullb *nullb = data;
struct nullb_queue *nq = &nullb->queues[index];

hctx->driver_data = nq;
null_init_queue(nullb, nq);
nullb->nr_queues++;

return 0;
}

static const struct blk_mq_ops null_mq_ops = {
.queue_rq = null_queue_rq,
.init_hctx = null_init_hctx,
.complete = null_softirq_done_fn,
};

Expand Down Expand Up @@ -592,8 +575,8 @@ static void null_del_dev(struct nullb *nullb)
else
del_gendisk(nullb->disk);
blk_cleanup_queue(nullb->q);
if (queue_mode == NULL_Q_MQ)
blk_mq_free_tag_set(&nullb->tag_set);
if (queue_mode == NULL_Q_MQ && nullb->tag_set == &nullb->__tag_set)
blk_mq_free_tag_set(nullb->tag_set);
if (!use_lightnvm)
put_disk(nullb->disk);
cleanup_queues(nullb);
Expand All @@ -615,6 +598,32 @@ static const struct block_device_operations null_fops = {
.release = null_release,
};

static void null_init_queue(struct nullb *nullb, struct nullb_queue *nq)
{
BUG_ON(!nullb);
BUG_ON(!nq);

init_waitqueue_head(&nq->wait);
nq->queue_depth = nullb->queue_depth;
}

static void null_init_queues(struct nullb *nullb)
{
struct request_queue *q = nullb->q;
struct blk_mq_hw_ctx *hctx;
struct nullb_queue *nq;
int i;

queue_for_each_hw_ctx(q, hctx, i) {
if (!hctx->nr_ctx || !hctx->tags)
continue;
nq = &nullb->queues[i];
hctx->driver_data = nq;
null_init_queue(nullb, nq);
nullb->nr_queues++;
}
}

static int setup_commands(struct nullb_queue *nq)
{
struct nullb_cmd *cmd;
Expand Down Expand Up @@ -695,6 +704,22 @@ static int null_gendisk_register(struct nullb *nullb)
return 0;
}

static int null_init_tag_set(struct blk_mq_tag_set *set)
{
set->ops = &null_mq_ops;
set->nr_hw_queues = submit_queues;
set->queue_depth = hw_queue_depth;
set->numa_node = home_node;
set->cmd_size = sizeof(struct nullb_cmd);
set->flags = BLK_MQ_F_SHOULD_MERGE;
set->driver_data = NULL;

if (blocking)
set->flags |= BLK_MQ_F_BLOCKING;

return blk_mq_alloc_tag_set(set);
}

static int null_add_dev(void)
{
struct nullb *nullb;
Expand All @@ -716,26 +741,23 @@ static int null_add_dev(void)
goto out_free_nullb;

if (queue_mode == NULL_Q_MQ) {
nullb->tag_set.ops = &null_mq_ops;
nullb->tag_set.nr_hw_queues = submit_queues;
nullb->tag_set.queue_depth = hw_queue_depth;
nullb->tag_set.numa_node = home_node;
nullb->tag_set.cmd_size = sizeof(struct nullb_cmd);
nullb->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
nullb->tag_set.driver_data = nullb;

if (blocking)
nullb->tag_set.flags |= BLK_MQ_F_BLOCKING;

rv = blk_mq_alloc_tag_set(&nullb->tag_set);
if (shared_tags) {
nullb->tag_set = &tag_set;
rv = 0;
} else {
nullb->tag_set = &nullb->__tag_set;
rv = null_init_tag_set(nullb->tag_set);
}

if (rv)
goto out_cleanup_queues;

nullb->q = blk_mq_init_queue(&nullb->tag_set);
nullb->q = blk_mq_init_queue(nullb->tag_set);
if (IS_ERR(nullb->q)) {
rv = -ENOMEM;
goto out_cleanup_tags;
}
null_init_queues(nullb);
} else if (queue_mode == NULL_Q_BIO) {
nullb->q = blk_alloc_queue_node(GFP_KERNEL, home_node);
if (!nullb->q) {
Expand Down Expand Up @@ -788,8 +810,8 @@ static int null_add_dev(void)
out_cleanup_blk_queue:
blk_cleanup_queue(nullb->q);
out_cleanup_tags:
if (queue_mode == NULL_Q_MQ)
blk_mq_free_tag_set(&nullb->tag_set);
if (queue_mode == NULL_Q_MQ && nullb->tag_set == &nullb->__tag_set)
blk_mq_free_tag_set(nullb->tag_set);
out_cleanup_queues:
cleanup_queues(nullb);
out_free_nullb:
Expand Down Expand Up @@ -822,6 +844,9 @@ static int __init null_init(void)
queue_mode = NULL_Q_MQ;
}

if (queue_mode == NULL_Q_MQ && shared_tags)
null_init_tag_set(&tag_set);

if (queue_mode == NULL_Q_MQ && use_per_node_hctx) {
if (submit_queues < nr_online_nodes) {
pr_warn("null_blk: submit_queues param is set to %u.",
Expand Down Expand Up @@ -882,6 +907,9 @@ static void __exit null_exit(void)
}
mutex_unlock(&lock);

if (queue_mode == NULL_Q_MQ && shared_tags)
blk_mq_free_tag_set(&tag_set);

kmem_cache_destroy(ppa_cache);
}

Expand Down

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