lkml.org 
[lkml]   [2019]   [Mar]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH 1/8] blk-mq: get rid of the synchronize_rcu in __blk_mq_update_nr_hw_queues
On Fri, Mar 15, 2019 at 5:07 PM Jianchao Wang
<jianchao.w.wang@oracle.com> wrote:
>
> In commit 530ca2c (blk-mq: Allow blocking queue tag iter callbacks),
> we try to get a non-zero q_usage_counter to avoid access hctxs that
> being modified. So the synchronize_rcu is useless and should be
> removed.
>
> Signed-off-by: Jianchao Wang <jianchao.w.wang@oracle.com>
> ---
> block/blk-mq-tag.c | 4 +---
> block/blk-mq.c | 4 ----
> 2 files changed, 1 insertion(+), 7 deletions(-)
>
> diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
> index 2089c6c..b792537 100644
> --- a/block/blk-mq-tag.c
> +++ b/block/blk-mq-tag.c
> @@ -384,9 +384,7 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn,
> /*
> * __blk_mq_update_nr_hw_queues() updates nr_hw_queues and queue_hw_ctx
> * while the queue is frozen. So we can use q_usage_counter to avoid
> - * racing with it. __blk_mq_update_nr_hw_queues() uses
> - * synchronize_rcu() to ensure this function left the critical section
> - * below.
> + * racing with it.
> */
> if (!percpu_ref_tryget(&q->q_usage_counter))
> return;
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 9437a5e..07584a9 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -3208,10 +3208,6 @@ 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
> * updating the new sw to hw queue mappings.
> --
> 2.7.4
>

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

Thanks,
Ming Lei

\
 
 \ /
  Last update: 2019-03-17 07:15    [W:0.113 / U:0.940 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site