Re: [PATCH 3/9] blk-mq: Relocate shared sbitmap resize in blk_mq_update_nr_requests()

Ming Lei
2021-07-20T07:52:52Z

On Wed, Jul 14, 2021 at 11:06:29PM +0800, John Garry wrote:
> For shared sbitmap, if the call to blk_mq_tag_update_depth() was
> successful for any hctx when hctx->sched_tags is not set, then it would be
> successful for all (due to nature in which blk_mq_tag_update_depth()
> fails).
>
> As such, there is no need to call blk_mq_tag_resize_shared_sbitmap() for
> each hctx. So relocate the call until after the hctx iteration under the
> !q->elevator check, which is equivalent (to !hctx->sched_tags).
>
> Signed-off-by: John Garry <john.garry@huawei.com>
> ---
> block/blk-mq.c | 13 ++++++++-----
> 1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index ae28f470893c..56e3c6fdba60 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -3624,8 +3624,6 @@ int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)
> if (!hctx->sched_tags) {
> ret = blk_mq_tag_update_depth(hctx, &hctx->tags, nr,
> false);
> - if (!ret && blk_mq_is_sbitmap_shared(set->flags))
> - blk_mq_tag_resize_shared_sbitmap(set, nr);
> } else {
> ret = blk_mq_tag_update_depth(hctx, &hctx->sched_tags,
> nr, true);
> @@ -3643,9 +3641,14 @@ int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)
> }
> if (!ret) {
> q->nr_requests = nr;
> - if (q->elevator && blk_mq_is_sbitmap_shared(set->flags))
> - sbitmap_queue_resize(&q->sched_bitmap_tags,
> - nr - set->reserved_tags);
> + if (blk_mq_is_sbitmap_shared(set->flags)) {
> + if (q->elevator) {
> + sbitmap_queue_resize(&q->sched_bitmap_tags,
> + nr - set->reserved_tags);
> + } else {
> + blk_mq_tag_resize_shared_sbitmap(set, nr);
> + }

The above two {} can be removed.

--
Ming