[PATCH v3 1/2] block: Add iocontext priority to request

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Patch adds an association between iocontext ioprio and the ioprio of
a request. This feature is only enabled if a queue flag is set to
indicate that requests should have ioprio associated with them. The
queue flag is exposed as the req_prio queue sysfs entry.

Signed-off-by: Adam Mananzanares <adam.manzanares@xxxxxxxx>
---
 Documentation/block/queue-sysfs.txt | 12 ++++++++++++
 block/blk-core.c                    |  5 +++++
 block/blk-sysfs.c                   | 32 ++++++++++++++++++++++++++++++++
 include/linux/blkdev.h              |  3 +++
 4 files changed, 52 insertions(+)

diff --git a/Documentation/block/queue-sysfs.txt b/Documentation/block/queue-sysfs.txt
index 2a39040..3ca4e8f 100644
--- a/Documentation/block/queue-sysfs.txt
+++ b/Documentation/block/queue-sysfs.txt
@@ -144,6 +144,18 @@ For storage configurations that need to maximize distribution of completion
 processing setting this option to '2' forces the completion to run on the
 requesting cpu (bypassing the "group" aggregation logic).
 
+rq_ioc_prio (RW)
+----------------
+If this option is '1', and there is a valid iocontext associated with the
+issuing context, and the bio we are processing does not have a valid
+prio, then we save the prio value from the iocontext with the request.
+
+This feature can be combined with device drivers that are aware of prio
+values in order to handle prio accordingly. An example would be if the ata
+layer recognizes prio and creates ata commands with high priority and sends
+them to the device. If the hardware supports priorities for commands then
+this has the potential to speed up response times for high priority IO.
+
 scheduler (RW)
 --------------
 When read, this file will display the current and available IO schedulers
diff --git a/block/blk-core.c b/block/blk-core.c
index 14d7c07..2e740c4 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -33,6 +33,7 @@
 #include <linux/ratelimit.h>
 #include <linux/pm_runtime.h>
 #include <linux/blk-cgroup.h>
+#include <linux/ioprio.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/block.h>
@@ -1648,6 +1649,7 @@ unsigned int blk_plug_queued_count(struct request_queue *q)
 
 void init_request_from_bio(struct request *req, struct bio *bio)
 {
+	struct io_context *ioc = rq_ioc(bio);
 	req->cmd_type = REQ_TYPE_FS;
 
 	req->cmd_flags |= bio->bi_opf & REQ_COMMON_MASK;
@@ -1657,6 +1659,9 @@ void init_request_from_bio(struct request *req, struct bio *bio)
 	req->errors = 0;
 	req->__sector = bio->bi_iter.bi_sector;
 	req->ioprio = bio_prio(bio);
+	if (blk_queue_rq_ioc_prio(req->q) && !ioprio_valid(req->ioprio) && ioc)
+		req->ioprio = ioc->ioprio;
+
 	blk_rq_bio_prep(req->q, req, bio);
 }
 
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 9cc8d7c..a9c5105 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -384,6 +384,31 @@ static ssize_t queue_dax_show(struct request_queue *q, char *page)
 	return queue_var_show(blk_queue_dax(q), page);
 }
 
+static ssize_t queue_rq_ioc_prio_show(struct request_queue *q, char *page)
+{
+	return queue_var_show(blk_queue_rq_ioc_prio(q), page);
+}
+
+static ssize_t queue_rq_ioc_prio_store(struct request_queue *q,
+				       const char *page, size_t count)
+{
+	unsigned long rq_ioc_prio_on;
+	ssize_t ret;
+
+	ret = queue_var_store(&rq_ioc_prio_on, page, count);
+	if (ret < 0)
+		return ret;
+
+	spin_lock_irq(q->queue_lock);
+	if (rq_ioc_prio_on)
+		queue_flag_set(QUEUE_FLAG_RQ_IOC_PRIO, q);
+	else
+		queue_flag_clear(QUEUE_FLAG_RQ_IOC_PRIO, q);
+	spin_unlock_irq(q->queue_lock);
+
+	return ret;
+}
+
 static struct queue_sysfs_entry queue_requests_entry = {
 	.attr = {.name = "nr_requests", .mode = S_IRUGO | S_IWUSR },
 	.show = queue_requests_show,
@@ -526,6 +551,12 @@ static struct queue_sysfs_entry queue_dax_entry = {
 	.show = queue_dax_show,
 };
 
+static struct queue_sysfs_entry queue_rq_ioc_prio_entry = {
+	.attr = {.name = "rq_ioc_prio", .mode = S_IRUGO | S_IWUSR },
+	.show = queue_rq_ioc_prio_show,
+	.store = queue_rq_ioc_prio_store,
+};
+
 static struct attribute *default_attrs[] = {
 	&queue_requests_entry.attr,
 	&queue_ra_entry.attr,
@@ -553,6 +584,7 @@ static struct attribute *default_attrs[] = {
 	&queue_poll_entry.attr,
 	&queue_wc_entry.attr,
 	&queue_dax_entry.attr,
+	&queue_rq_ioc_prio_entry.attr,
 	NULL,
 };
 
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index c47c358..63b842a 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -505,6 +505,7 @@ struct request_queue {
 #define QUEUE_FLAG_FUA	       24	/* device supports FUA writes */
 #define QUEUE_FLAG_FLUSH_NQ    25	/* flush not queueuable */
 #define QUEUE_FLAG_DAX         26	/* device supports DAX */
+#define QUEUE_FLAG_RQ_IOC_PRIO 27	/* Use iocontext ioprio */
 
 #define QUEUE_FLAG_DEFAULT	((1 << QUEUE_FLAG_IO_STAT) |		\
 				 (1 << QUEUE_FLAG_STACKABLE)	|	\
@@ -595,6 +596,8 @@ static inline void queue_flag_clear(unsigned int flag, struct request_queue *q)
 #define blk_queue_secure_erase(q) \
 	(test_bit(QUEUE_FLAG_SECERASE, &(q)->queue_flags))
 #define blk_queue_dax(q)	test_bit(QUEUE_FLAG_DAX, &(q)->queue_flags)
+#define blk_queue_rq_ioc_prio(q) \
+	test_bit(QUEUE_FLAG_RQ_IOC_PRIO, &(q)->queue_flags)
 
 #define blk_noretry_request(rq) \
 	((rq)->cmd_flags & (REQ_FAILFAST_DEV|REQ_FAILFAST_TRANSPORT| \
-- 
2.1.4

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