null_blk: poll queue support
There's currently no way to experiment with polled IO with null_blk,
which seems like an oversight. This patch adds support for polled IO.
We keep a list of issued IOs on submit, and then process that list
when mq_ops->poll() is invoked.
A new parameter is added, poll_queues. It defaults to 1 like the
submit queues, meaning we'll have 1 poll queue available.
Fixes-by: Bart Van Assche <bvanassche@acm.org>
Fixes-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Link: https://lore.kernel.org/r/baca710d-0f2a-16e2-60bd-b105b854e0ae@kernel.dk
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
index e5cbcf5..f4af95c 100644
--- a/drivers/block/null_blk/main.c
+++ b/drivers/block/null_blk/main.c
@@ -92,6 +92,10 @@ static int g_submit_queues = 1;
module_param_named(submit_queues, g_submit_queues, int, 0444);
MODULE_PARM_DESC(submit_queues, "Number of submission queues");
+static int g_poll_queues = 1;
+module_param_named(poll_queues, g_poll_queues, int, 0444);
+MODULE_PARM_DESC(poll_queues, "Number of IOPOLL submission queues");
+
static int g_home_node = NUMA_NO_NODE;
module_param_named(home_node, g_home_node, int, 0444);
MODULE_PARM_DESC(home_node, "Home node for the device");
@@ -347,6 +351,7 @@ static int nullb_apply_submit_queues(struct nullb_device *dev,
NULLB_DEVICE_ATTR(size, ulong, NULL);
NULLB_DEVICE_ATTR(completion_nsec, ulong, NULL);
NULLB_DEVICE_ATTR(submit_queues, uint, nullb_apply_submit_queues);
+NULLB_DEVICE_ATTR(poll_queues, uint, nullb_apply_submit_queues);
NULLB_DEVICE_ATTR(home_node, uint, NULL);
NULLB_DEVICE_ATTR(queue_mode, uint, NULL);
NULLB_DEVICE_ATTR(blocksize, uint, NULL);
@@ -466,6 +471,7 @@ static struct configfs_attribute *nullb_device_attrs[] = {
&nullb_device_attr_size,
&nullb_device_attr_completion_nsec,
&nullb_device_attr_submit_queues,
+ &nullb_device_attr_poll_queues,
&nullb_device_attr_home_node,
&nullb_device_attr_queue_mode,
&nullb_device_attr_blocksize,
@@ -593,6 +599,7 @@ static struct nullb_device *null_alloc_dev(void)
dev->size = g_gb * 1024;
dev->completion_nsec = g_completion_nsec;
dev->submit_queues = g_submit_queues;
+ dev->poll_queues = g_poll_queues;
dev->home_node = g_home_node;
dev->queue_mode = g_queue_mode;
dev->blocksize = g_bs;
@@ -1454,12 +1461,80 @@ static bool should_requeue_request(struct request *rq)
return false;
}
+static int null_map_queues(struct blk_mq_tag_set *set)
+{
+ struct nullb *nullb = set->driver_data;
+ int i, qoff;
+
+ for (i = 0, qoff = 0; i < set->nr_maps; i++) {
+ struct blk_mq_queue_map *map = &set->map[i];
+
+ switch (i) {
+ case HCTX_TYPE_DEFAULT:
+ if (nullb)
+ map->nr_queues = nullb->dev->submit_queues;
+ else
+ map->nr_queues = g_submit_queues;
+ break;
+ case HCTX_TYPE_READ:
+ map->nr_queues = 0;
+ continue;
+ case HCTX_TYPE_POLL:
+ if (nullb)
+ map->nr_queues = nullb->dev->poll_queues;
+ else
+ map->nr_queues = g_poll_queues;
+ break;
+ }
+ map->queue_offset = qoff;
+ qoff += map->nr_queues;
+ blk_mq_map_queues(map);
+ }
+
+ return 0;
+}
+
+static int null_poll(struct blk_mq_hw_ctx *hctx, struct io_comp_batch *iob)
+{
+ struct nullb_queue *nq = hctx->driver_data;
+ LIST_HEAD(list);
+ int nr = 0;
+
+ spin_lock(&nq->poll_lock);
+ list_splice_init(&nq->poll_list, &list);
+ spin_unlock(&nq->poll_lock);
+
+ while (!list_empty(&list)) {
+ struct nullb_cmd *cmd;
+ struct request *req;
+
+ req = list_first_entry(&list, struct request, queuelist);
+ list_del_init(&req->queuelist);
+ cmd = blk_mq_rq_to_pdu(req);
+ cmd->error = null_process_cmd(cmd, req_op(req), blk_rq_pos(req),
+ blk_rq_sectors(req));
+ end_cmd(cmd);
+ nr++;
+ }
+
+ return nr;
+}
+
static enum blk_eh_timer_return null_timeout_rq(struct request *rq, bool res)
{
+ struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
struct nullb_cmd *cmd = blk_mq_rq_to_pdu(rq);
pr_info("rq %p timed out\n", rq);
+ if (hctx->type == HCTX_TYPE_POLL) {
+ struct nullb_queue *nq = hctx->driver_data;
+
+ spin_lock(&nq->poll_lock);
+ list_del_init(&rq->queuelist);
+ spin_unlock(&nq->poll_lock);
+ }
+
/*
* If the device is marked as blocking (i.e. memory backed or zoned
* device), the submission path may be blocked waiting for resources
@@ -1480,10 +1555,11 @@ static blk_status_t null_queue_rq(struct blk_mq_hw_ctx *hctx,
struct nullb_queue *nq = hctx->driver_data;
sector_t nr_sectors = blk_rq_sectors(bd->rq);
sector_t sector = blk_rq_pos(bd->rq);
+ const bool is_poll = hctx->type == HCTX_TYPE_POLL;
might_sleep_if(hctx->flags & BLK_MQ_F_BLOCKING);
- if (nq->dev->irqmode == NULL_IRQ_TIMER) {
+ if (!is_poll && nq->dev->irqmode == NULL_IRQ_TIMER) {
hrtimer_init(&cmd->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
cmd->timer.function = null_cmd_timer_expired;
}
@@ -1507,6 +1583,13 @@ static blk_status_t null_queue_rq(struct blk_mq_hw_ctx *hctx,
return BLK_STS_OK;
}
}
+
+ if (is_poll) {
+ spin_lock(&nq->poll_lock);
+ list_add_tail(&bd->rq->queuelist, &nq->poll_list);
+ spin_unlock(&nq->poll_lock);
+ return BLK_STS_OK;
+ }
if (cmd->fake_timeout)
return BLK_STS_OK;
@@ -1542,6 +1625,8 @@ static void null_init_queue(struct nullb *nullb, struct nullb_queue *nq)
init_waitqueue_head(&nq->wait);
nq->queue_depth = nullb->queue_depth;
nq->dev = nullb->dev;
+ INIT_LIST_HEAD(&nq->poll_list);
+ spin_lock_init(&nq->poll_lock);
}
static int null_init_hctx(struct blk_mq_hw_ctx *hctx, void *driver_data,
@@ -1567,6 +1652,8 @@ static const struct blk_mq_ops null_mq_ops = {
.queue_rq = null_queue_rq,
.complete = null_complete_rq,
.timeout = null_timeout_rq,
+ .poll = null_poll,
+ .map_queues = null_map_queues,
.init_hctx = null_init_hctx,
.exit_hctx = null_exit_hctx,
};
@@ -1663,13 +1750,17 @@ static int setup_commands(struct nullb_queue *nq)
static int setup_queues(struct nullb *nullb)
{
- nullb->queues = kcalloc(nr_cpu_ids, sizeof(struct nullb_queue),
+ int nqueues = nr_cpu_ids;
+
+ if (g_poll_queues)
+ nqueues += g_poll_queues;
+
+ nullb->queues = kcalloc(nqueues, sizeof(struct nullb_queue),
GFP_KERNEL);
if (!nullb->queues)
return -ENOMEM;
nullb->queue_depth = nullb->dev->hw_queue_depth;
-
return 0;
}
@@ -1721,9 +1812,14 @@ static int null_gendisk_register(struct nullb *nullb)
static int null_init_tag_set(struct nullb *nullb, struct blk_mq_tag_set *set)
{
+ int poll_queues;
+
set->ops = &null_mq_ops;
set->nr_hw_queues = nullb ? nullb->dev->submit_queues :
g_submit_queues;
+ poll_queues = nullb ? nullb->dev->poll_queues : g_poll_queues;
+ if (poll_queues)
+ set->nr_hw_queues += poll_queues;
set->queue_depth = nullb ? nullb->dev->hw_queue_depth :
g_hw_queue_depth;
set->numa_node = nullb ? nullb->dev->home_node : g_home_node;
@@ -1733,7 +1829,11 @@ static int null_init_tag_set(struct nullb *nullb, struct blk_mq_tag_set *set)
set->flags |= BLK_MQ_F_NO_SCHED;
if (g_shared_tag_bitmap)
set->flags |= BLK_MQ_F_TAG_HCTX_SHARED;
- set->driver_data = NULL;
+ set->driver_data = nullb;
+ if (g_poll_queues)
+ set->nr_maps = 3;
+ else
+ set->nr_maps = 1;
if ((nullb && nullb->dev->blocking) || g_blocking)
set->flags |= BLK_MQ_F_BLOCKING;
diff --git a/drivers/block/null_blk/null_blk.h b/drivers/block/null_blk/null_blk.h
index 64bef12..90c3eef 100644
--- a/drivers/block/null_blk/null_blk.h
+++ b/drivers/block/null_blk/null_blk.h
@@ -32,6 +32,9 @@ struct nullb_queue {
struct nullb_device *dev;
unsigned int requeue_selection;
+ struct list_head poll_list;
+ spinlock_t poll_lock;
+
struct nullb_cmd *cmds;
};
@@ -83,6 +86,7 @@ struct nullb_device {
unsigned int zone_max_open; /* max number of open zones */
unsigned int zone_max_active; /* max number of active zones */
unsigned int submit_queues; /* number of submission queues */
+ unsigned int poll_queues; /* number of IOPOLL submission queues */
unsigned int home_node; /* home node for the device */
unsigned int queue_mode; /* block interface */
unsigned int blocksize; /* block size */
