[1/4] block: Remove the synchronize_rcu() call from __blk_mq_update_nr_hw_queues()
diff mbox series

Message ID 20191021224259.209542-2-bvanassche@acm.org
State New
Headers show
Series
  • Reduce the amount of memory required for request queues
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Commit Message

Bart Van Assche Oct. 21, 2019, 10:42 p.m. UTC
Since the blk_mq_{,un}freeze_queue() calls in __blk_mq_update_nr_hw_queues()
already serialize __blk_mq_update_nr_hw_queues() against
blk_mq_queue_tag_busy_iter(), the synchronize_rcu() call in
__blk_mq_update_nr_hw_queues() is not necessary. Hence remove it.

Note: the synchronize_rcu() call in __blk_mq_update_nr_hw_queues() was
introduced by commit f5bbbbe4d635 ("blk-mq: sync the update nr_hw_queues with
blk_mq_queue_tag_busy_iter"). Commit 530ca2c9bd69 ("blk-mq: Allow blocking
queue tag iter callbacks") removed the rcu_read_{,un}lock() calls that
correspond to the synchronize_rcu() call in __blk_mq_update_nr_hw_queues().

Cc: Christoph Hellwig <hch@infradead.org>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 block/blk-mq.c | 4 ----
 1 file changed, 4 deletions(-)

Comments

Ming Lei Oct. 22, 2019, 9:32 a.m. UTC | #1
On Mon, Oct 21, 2019 at 03:42:56PM -0700, Bart Van Assche wrote:
> Since the blk_mq_{,un}freeze_queue() calls in __blk_mq_update_nr_hw_queues()
> already serialize __blk_mq_update_nr_hw_queues() against
> blk_mq_queue_tag_busy_iter(), the synchronize_rcu() call in
> __blk_mq_update_nr_hw_queues() is not necessary. Hence remove it.
> 
> Note: the synchronize_rcu() call in __blk_mq_update_nr_hw_queues() was
> introduced by commit f5bbbbe4d635 ("blk-mq: sync the update nr_hw_queues with
> blk_mq_queue_tag_busy_iter"). Commit 530ca2c9bd69 ("blk-mq: Allow blocking
> queue tag iter callbacks") removed the rcu_read_{,un}lock() calls that
> correspond to the synchronize_rcu() call in __blk_mq_update_nr_hw_queues().
> 
> Cc: Christoph Hellwig <hch@infradead.org>
> Cc: Ming Lei <ming.lei@redhat.com>
> Cc: Hannes Reinecke <hare@suse.com>
> Cc: Johannes Thumshirn <jthumshirn@suse.de>
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> ---
>  block/blk-mq.c | 4 ----
>  1 file changed, 4 deletions(-)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 8538dc415499..7528678ef41f 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -3242,10 +3242,6 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
>  
>  	list_for_each_entry(q, &set->tag_list, tag_set_list)
>  		blk_mq_freeze_queue(q);
> -	/*
> -	 * Sync with blk_mq_queue_tag_busy_iter.
> -	 */
> -	synchronize_rcu();
>  	/*
>  	 * Switch IO scheduler to 'none', cleaning up the data associated
>  	 * with the previous scheduler. We will switch back once we are done
> -- 
> 2.23.0.866.gb869b98d4c-goog
> 

Reviewed-by: Ming Lei <ming.lei@redhat.com>

Patch
diff mbox series

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 8538dc415499..7528678ef41f 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -3242,10 +3242,6 @@  static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
 
 	list_for_each_entry(q, &set->tag_list, tag_set_list)
 		blk_mq_freeze_queue(q);
-	/*
-	 * Sync with blk_mq_queue_tag_busy_iter.
-	 */
-	synchronize_rcu();
 	/*
 	 * Switch IO scheduler to 'none', cleaning up the data associated
 	 * with the previous scheduler. We will switch back once we are done