On Thu, May 10, 2018 at 10:24:25AM -0600, Jens Axboe wrote:
> If our shallow depth is smaller than the wake batching of sbitmap,
> we can introduce hangs. Ensure that sbitmap knows how low we'll go.
>
> Acked-by: Paolo Valente <paolo.valente@xxxxxxxxxx>
Reviewed-by: Omar Sandoval <osandov@xxxxxx>
> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
> ---
> block/bfq-iosched.c | 17 ++++++++++++++---
> 1 file changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
> index 10294124d597..b622e73a326a 100644
> --- a/block/bfq-iosched.c
> +++ b/block/bfq-iosched.c
> @@ -5081,10 +5081,13 @@ void bfq_put_async_queues(struct bfq_data *bfqd, struct bfq_group *bfqg)
>
> /*
> * See the comments on bfq_limit_depth for the purpose of
> - * the depths set in the function.
> + * the depths set in the function. Return minimum shallow depth we'll use.
> */
> -static void bfq_update_depths(struct bfq_data *bfqd, struct sbitmap_queue *bt)
> +static unsigned int bfq_update_depths(struct bfq_data *bfqd,
> + struct sbitmap_queue *bt)
> {
> + unsigned int i, j, min_shallow = UINT_MAX;
> +
> /*
> * In-word depths if no bfq_queue is being weight-raised:
> * leaving 25% of tags only for sync reads.
> @@ -5115,14 +5118,22 @@ static void bfq_update_depths(struct bfq_data *bfqd, struct sbitmap_queue *bt)
> bfqd->word_depths[1][0] = max(((1U << bt->sb.shift) * 3) >> 4, 1U);
> /* no more than ~37% of tags for sync writes (~20% extra tags) */
> bfqd->word_depths[1][1] = max(((1U << bt->sb.shift) * 6) >> 4, 1U);
> +
> + for (i = 0; i < 2; i++)
> + for (j = 0; j < 2; j++)
> + min_shallow = min(min_shallow, bfqd->word_depths[i][j]);
> +
> + return min_shallow;
> }
>
> static int bfq_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int index)
> {
> struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
> struct blk_mq_tags *tags = hctx->sched_tags;
> + unsigned int min_shallow;
>
> - bfq_update_depths(bfqd, &tags->bitmap_tags);
> + min_shallow = bfq_update_depths(bfqd, &tags->bitmap_tags);
> + sbitmap_queue_min_shallow_depth(&tags->bitmap_tags, min_shallow);
> return 0;
> }
>
> --
> 2.7.4
>
