For interactive workloads it is important that synchronous requests are
not delayed. Hence reserve 25% of tags for synchronous requests. This patch
still allows asynchronous requests to fill the hardware queues since
blk_mq_init_sched() makes sure that the number of scheduler requests is the
double of the hardware queue depth. From blk_mq_init_sched():
q->nr_requests = 2 * min_t(unsigned int, q->tag_set->queue_depth,
BLKDEV_MAX_RQ);
Cc: Damien Le Moal <damien.lemoal@xxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Ming Lei <ming.lei@xxxxxxxxxx>
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
block/mq-deadline.c | 46 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 46 insertions(+)
diff --git a/block/mq-deadline.c b/block/mq-deadline.c
index 2ab844a4b6b5..81f487d77e09 100644
--- a/block/mq-deadline.c
+++ b/block/mq-deadline.c
@@ -69,6 +69,7 @@ struct deadline_data {
int fifo_batch;
int writes_starved;
int front_merges;
+ u32 async_depth;
spinlock_t lock;
spinlock_t zone_lock;
@@ -399,6 +400,38 @@ static struct request *dd_dispatch_request(struct blk_mq_hw_ctx *hctx)
return rq;
}
+static void dd_limit_depth(unsigned int op, struct blk_mq_alloc_data *data)
+{
+ struct deadline_data *dd = data->q->elevator->elevator_data;
+
+ /* Do not throttle synchronous reads. */
+ if (op_is_sync(op) && !op_is_write(op))
+ return;
+
+ /*
+ * Throttle asynchronous requests and writes such that these requests
+ * do not block the allocation of synchronous requests.
+ */
+ data->shallow_depth = dd->async_depth;
+}
+
+static void dd_depth_updated(struct blk_mq_hw_ctx *hctx)
+{
+ struct request_queue *q = hctx->queue;
+ struct deadline_data *dd = q->elevator->elevator_data;
+ struct blk_mq_tags *tags = hctx->sched_tags;
+
+ dd->async_depth = 3 * q->nr_requests / 4;
+
+ sbitmap_queue_min_shallow_depth(tags->bitmap_tags, dd->async_depth);
+}
+
+static int dd_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
+{
+ dd_depth_updated(hctx);
+ return 0;
+}
+
static void dd_exit_sched(struct elevator_queue *e)
{
struct deadline_data *dd = e->elevator_data;
@@ -744,6 +777,15 @@ static int deadline_starved_show(void *data, struct seq_file *m)
return 0;
}
+static int dd_async_depth_show(void *data, struct seq_file *m)
+{
+ struct request_queue *q = data;
+ struct deadline_data *dd = q->elevator->elevator_data;
+
+ seq_printf(m, "%u\n", dd->async_depth);
+ return 0;
+}
+
static void *deadline_dispatch_start(struct seq_file *m, loff_t *pos)
__acquires(&dd->lock)
{
@@ -786,6 +828,7 @@ static const struct blk_mq_debugfs_attr deadline_queue_debugfs_attrs[] = {
DEADLINE_QUEUE_DDIR_ATTRS(write),
{"batching", 0400, deadline_batching_show},
{"starved", 0400, deadline_starved_show},
+ {"async_depth", 0400, dd_async_depth_show},
{"dispatch", 0400, .seq_ops = &deadline_dispatch_seq_ops},
{},
};
@@ -794,6 +837,8 @@ static const struct blk_mq_debugfs_attr deadline_queue_debugfs_attrs[] = {
static struct elevator_type mq_deadline = {
.ops = {
+ .depth_updated = dd_depth_updated,
+ .limit_depth = dd_limit_depth,
.insert_requests = dd_insert_requests,
.dispatch_request = dd_dispatch_request,
.prepare_request = dd_prepare_request,
@@ -807,6 +852,7 @@ static struct elevator_type mq_deadline = {
.has_work = dd_has_work,
.init_sched = dd_init_sched,
.exit_sched = dd_exit_sched,
+ .init_hctx = dd_init_hctx,
},
#ifdef CONFIG_BLK_DEBUG_FS
