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Subject[PATCH 8/9] block: add code to track actual device queue depth
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For blk-mq, ->nr_requests does track queue depth, at least at init
time. But for the older queue paths, it's simply a soft setting.
On top of that, it's generally larger than the hardware setting
on purpose, to allow backup of requests for merging.

Fill a hole in struct request with a 'queue_depth' member, that
drivers can call to more closely inform the block layer of the
real queue depth.

Signed-off-by: Jens Axboe <axboe@fb.com>
---
block/blk-settings.c | 6 ++++++
drivers/scsi/scsi.c | 3 +++
include/linux/blkdev.h | 11 +++++++++++
3 files changed, 20 insertions(+)

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 4dbd511a9889..06e01682f827 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -820,6 +820,12 @@ void blk_queue_update_dma_alignment(struct request_queue *q, int mask)
}
EXPORT_SYMBOL(blk_queue_update_dma_alignment);

+void blk_set_queue_depth(struct request_queue *q, unsigned int depth)
+{
+ q->queue_depth = depth;
+}
+EXPORT_SYMBOL(blk_set_queue_depth);
+
/**
* blk_queue_flush - configure queue's cache flush capability
* @q: the request queue for the device
diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index b1bf42b93fcc..6503724865e7 100644
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -621,6 +621,9 @@ int scsi_change_queue_depth(struct scsi_device *sdev, int depth)
wmb();
}

+ if (sdev->request_queue)
+ blk_set_queue_depth(sdev->request_queue, depth);
+
return sdev->queue_depth;
}
EXPORT_SYMBOL(scsi_change_queue_depth);
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 76e875159e52..08b897b159d1 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -315,6 +315,8 @@ struct request_queue {
struct blk_mq_ctx __percpu *queue_ctx;
unsigned int nr_queues;

+ unsigned int queue_depth;
+
/* hw dispatch queues */
struct blk_mq_hw_ctx **queue_hw_ctx;
unsigned int nr_hw_queues;
@@ -683,6 +685,14 @@ static inline bool blk_write_same_mergeable(struct bio *a, struct bio *b)
return false;
}

+static inline unsigned int blk_queue_depth(struct request_queue *q)
+{
+ if (q->queue_depth)
+ return q->queue_depth;
+
+ return q->nr_requests;
+}
+
/*
* q->prep_rq_fn return values
*/
@@ -986,6 +996,7 @@ extern void blk_limits_io_min(struct queue_limits *limits, unsigned int min);
extern void blk_queue_io_min(struct request_queue *q, unsigned int min);
extern void blk_limits_io_opt(struct queue_limits *limits, unsigned int opt);
extern void blk_queue_io_opt(struct request_queue *q, unsigned int opt);
+extern void blk_set_queue_depth(struct request_queue *q, unsigned int depth);
extern void blk_set_default_limits(struct queue_limits *lim);
extern void blk_set_stacking_limits(struct queue_limits *lim);
extern int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
--
2.8.0.rc4.6.g7e4ba36
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