Re: [PATCH] block: Make writeback throttling defaults consistent for SQ devices

[Jan Kara <jack@suse.cz>]

On Wed 19-04-17 11:33:27, Jan Kara wrote:
> When CFQ is used as an elevator, it disables writeback throttling
> because they don't play well together. Later when a different elevator
> is chosen for the device, writeback throttling doesn't get enabled
> again as it should. Make sure CFQ enables writeback throttling (if it
> should be enabled by default) when we switch from it to another IO
> scheduler.
> 
> Signed-off-by: Jan Kara <jack@suse.cz>

Forgot to change header to v2 so I'm rather writing it here so that it's
clear.

								Honza

> ---
>  block/blk-sysfs.c | 19 +------------------
>  block/blk-wbt.c   | 19 +++++++++++++++++++
>  block/blk-wbt.h   |  4 ++++
>  block/elevator.c  |  3 +++
>  4 files changed, 27 insertions(+), 18 deletions(-)
> 
> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
> index fc20489f0d2b..f85723332288 100644
> --- a/block/blk-sysfs.c
> +++ b/block/blk-sysfs.c
> @@ -844,23 +844,6 @@ struct kobj_type blk_queue_ktype = {
>  	.release	= blk_release_queue,
>  };
>  
> -static void blk_wb_init(struct request_queue *q)
> -{
> -#ifndef CONFIG_BLK_WBT_MQ
> -	if (q->mq_ops)
> -		return;
> -#endif
> -#ifndef CONFIG_BLK_WBT_SQ
> -	if (q->request_fn)
> -		return;
> -#endif
> -
> -	/*
> -	 * If this fails, we don't get throttling
> -	 */
> -	wbt_init(q);
> -}
> -
>  int blk_register_queue(struct gendisk *disk)
>  {
>  	int ret;
> @@ -908,7 +891,7 @@ int blk_register_queue(struct gendisk *disk)
>  
>  	kobject_uevent(&q->kobj, KOBJ_ADD);
>  
> -	blk_wb_init(q);
> +	wbt_enable_default(q);
>  
>  	blk_throtl_register_queue(q);
>  
> diff --git a/block/blk-wbt.c b/block/blk-wbt.c
> index b3b79149d3a0..26e1bb617877 100644
> --- a/block/blk-wbt.c
> +++ b/block/blk-wbt.c
> @@ -665,6 +665,25 @@ void wbt_disable_default(struct request_queue *q)
>  }
>  EXPORT_SYMBOL_GPL(wbt_disable_default);
>  
> +/*
> + * Enable wbt if defaults are configured that way
> + */
> +void wbt_enable_default(struct request_queue *q)
> +{
> +	/* Throttling already enabled? */
> +	if (q->rq_wb)
> +		return;
> +
> +	/* Queue not registered? Maybe shutting down... */
> +	if (!test_bit(QUEUE_FLAG_REGISTERED, &q->queue_flags))
> +		return;
> +
> +	if ((q->mq_ops && IS_ENABLED(CONFIG_BLK_WBT_MQ)) ||
> +	    (q->request_fn && IS_ENABLED(CONFIG_BLK_WBT_SQ)))
> +		wbt_init(q);
> +}
> +EXPORT_SYMBOL_GPL(wbt_enable_default);
> +
>  u64 wbt_default_latency_nsec(struct request_queue *q)
>  {
>  	/*
> diff --git a/block/blk-wbt.h b/block/blk-wbt.h
> index ad6c78507c3a..df6de50c5d59 100644
> --- a/block/blk-wbt.h
> +++ b/block/blk-wbt.h
> @@ -117,6 +117,7 @@ void wbt_update_limits(struct rq_wb *);
>  void wbt_requeue(struct rq_wb *, struct blk_issue_stat *);
>  void wbt_issue(struct rq_wb *, struct blk_issue_stat *);
>  void wbt_disable_default(struct request_queue *);
> +void wbt_enable_default(struct request_queue *);
>  
>  void wbt_set_queue_depth(struct rq_wb *, unsigned int);
>  void wbt_set_write_cache(struct rq_wb *, bool);
> @@ -155,6 +156,9 @@ static inline void wbt_issue(struct rq_wb *rwb, struct blk_issue_stat *stat)
>  static inline void wbt_disable_default(struct request_queue *q)
>  {
>  }
> +static inline void wbt_enable_default(struct request_queue *q)
> +{
> +}
>  static inline void wbt_set_queue_depth(struct rq_wb *rwb, unsigned int depth)
>  {
>  }
> diff --git a/block/elevator.c b/block/elevator.c
> index dbeecf7be719..fb50416b5aae 100644
> --- a/block/elevator.c
> +++ b/block/elevator.c
> @@ -41,6 +41,7 @@
>  
>  #include "blk.h"
>  #include "blk-mq-sched.h"
> +#include "blk-wbt.h"
>  
>  static DEFINE_SPINLOCK(elv_list_lock);
>  static LIST_HEAD(elv_list);
> @@ -877,6 +878,8 @@ void elv_unregister_queue(struct request_queue *q)
>  		kobject_uevent(&e->kobj, KOBJ_REMOVE);
>  		kobject_del(&e->kobj);
>  		e->registered = 0;
> +		/* Re-enable throttling in case elevator disabled it */
> +		wbt_enable_default(q);
>  	}
>  }
>  EXPORT_SYMBOL(elv_unregister_queue);
> -- 
> 2.12.0
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR