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[PATCH 5/8] block: add code to track actual device queue depth

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  [PATCH 5/8] block: add code to track actual device queue depth Jens Axboe <axboe@fb.com> - 2016-11-01 22:20 +0100
    Re: [PATCH 5/8] block: add code to track actual device queue depth Christoph Hellwig <hch@lst.de> - 2016-11-02 16:00 +0100
      Re: [PATCH 5/8] block: add code to track actual device queue depth Johannes Thumshirn <jthumshirn@suse.de> - 2016-11-02 17:50 +0100
    Re: [PATCH 5/8] block: add code to track actual device queue depth Jan Kara <jack@suse.cz> - 2016-11-05 23:40 +0100

#1513516 — [PATCH 5/8] block: add code to track actual device queue depth

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   | 12 ++++++++++++
 drivers/scsi/scsi.c    |  3 +++
 include/linux/blkdev.h | 11 +++++++++++
 3 files changed, 26 insertions(+)

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 55369a65dea2..9cf053759363 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -837,6 +837,18 @@ void blk_queue_flush_queueable(struct request_queue *q, bool queueable)
 EXPORT_SYMBOL_GPL(blk_queue_flush_queueable);
 
 /**
+ * blk_set_queue_depth - tell the block layer about the device queue depth
+ * @q:		the request queue for the device
+ * @depth:		queue depth
+ *
+ */
+void blk_set_queue_depth(struct request_queue *q, unsigned int depth)
+{
+	q->queue_depth = depth;
+}
+EXPORT_SYMBOL(blk_set_queue_depth);
+
+/**
  * blk_queue_write_cache - configure queue's write cache
  * @q:		the request queue for the device
  * @wc:		write back cache on or off
diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index 1deb6adc411f..75455d4dab68 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 8396da2bb698..0c677fb35ce4 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -405,6 +405,8 @@ 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;
@@ -777,6 +779,14 @@ 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
  */
@@ -1093,6 +1103,7 @@ 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,
-- 
2.7.4

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#1513890

On Tue, Nov 01, 2016 at 03:08:48PM -0600, Jens Axboe wrote:
> 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

That would be struct request_queue..

>  /**
> + * blk_set_queue_depth - tell the block layer about the device queue depth
> + * @q:		the request queue for the device
> + * @depth:		queue depth
> + *
> + */
> +void blk_set_queue_depth(struct request_queue *q, unsigned int depth)
> +{
> +	q->queue_depth = depth;
> +}
> +EXPORT_SYMBOL(blk_set_queue_depth);

Do we really need this wrapper?

> +++ 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;

Can we kill the scsi_device queue_depth member and just always use
the request_queue one?

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#1513965

On Wed, Nov 02, 2016 at 09:02:08AM -0600, Jens Axboe wrote:
> On 11/02/2016 08:59 AM, Christoph Hellwig wrote:
> > On Tue, Nov 01, 2016 at 03:08:48PM -0600, Jens Axboe wrote:
> > > 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
> > 
> > That would be struct request_queue..
> 
> Good catch, will fix.
> 
> > >  /**
> > > + * blk_set_queue_depth - tell the block layer about the device queue depth
> > > + * @q:		the request queue for the device
> > > + * @depth:		queue depth
> > > + *
> > > + */
> > > +void blk_set_queue_depth(struct request_queue *q, unsigned int depth)
> > > +{
> > > +	q->queue_depth = depth;
> > > +}
> > > +EXPORT_SYMBOL(blk_set_queue_depth);
> > 
> > Do we really need this wrapper?
> 
> Not necessarily, just seems like a nicer API than manually setting the
> field. Not a big deal to me, though.

A lot of block code uses this kind of setters so I _think_ it complies with
the overall style. But I have no strong opinion on this either...

Byte,
	Johannes
-- 
Johannes Thumshirn                                          Storage
jthumshirn@suse.de                                +49 911 74053 689
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Felix Imendörffer, Jane Smithard, Graham Norton
HRB 21284 (AG Nürnberg)
Key fingerprint = EC38 9CAB C2C4 F25D 8600 D0D0 0393 969D 2D76 0850

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#1515637

On Tue 01-11-16 15:08:48, Jens Axboe wrote:
> 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>

The patch looks good to me. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza
> ---
>  block/blk-settings.c   | 12 ++++++++++++
>  drivers/scsi/scsi.c    |  3 +++
>  include/linux/blkdev.h | 11 +++++++++++
>  3 files changed, 26 insertions(+)
> 
> diff --git a/block/blk-settings.c b/block/blk-settings.c
> index 55369a65dea2..9cf053759363 100644
> --- a/block/blk-settings.c
> +++ b/block/blk-settings.c
> @@ -837,6 +837,18 @@ void blk_queue_flush_queueable(struct request_queue *q, bool queueable)
>  EXPORT_SYMBOL_GPL(blk_queue_flush_queueable);
>  
>  /**
> + * blk_set_queue_depth - tell the block layer about the device queue depth
> + * @q:		the request queue for the device
> + * @depth:		queue depth
> + *
> + */
> +void blk_set_queue_depth(struct request_queue *q, unsigned int depth)
> +{
> +	q->queue_depth = depth;
> +}
> +EXPORT_SYMBOL(blk_set_queue_depth);
> +
> +/**
>   * blk_queue_write_cache - configure queue's write cache
>   * @q:		the request queue for the device
>   * @wc:		write back cache on or off
> diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
> index 1deb6adc411f..75455d4dab68 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 8396da2bb698..0c677fb35ce4 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -405,6 +405,8 @@ 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;
> @@ -777,6 +779,14 @@ 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
>   */
> @@ -1093,6 +1103,7 @@ 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,
> -- 
> 2.7.4
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

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