On Thu, May 10, 2018 at 10:24:22AM -0600, Jens Axboe wrote:
> bfqd->sb_shift was attempted used as a cache for the sbitmap queue
> shift, but we don't need it, as it never changes. Kill it with fire.
>
> Acked-by: Paolo Valente
Reviewed-by: Omar Sandoval
> Signed-off-by: Jens Axboe
> ---
> block/bfq-iosched.c | 16 +++-
> block/bfq-iosched.h | 6 --
> 2 files changed, 7 insertions(+), 15 deletions(-)
>
> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
> index 0cd8aa80c32d..10294124d597 100644
> --- a/block/bfq-iosched.c
> +++ b/block/bfq-iosched.c
> @@ -5085,26 +5085,24 @@ void bfq_put_async_queues(struct bfq_data *bfqd,
> struct bfq_group *bfqg)
> */
> static void bfq_update_depths(struct bfq_data *bfqd, struct sbitmap_queue
> *bt)
> {
> - bfqd->sb_shift = bt->sb.shift;
> -
> /*
>* In-word depths if no bfq_queue is being weight-raised:
>* leaving 25% of tags only for sync reads.
>*
>* In next formulas, right-shift the value
> - * (1U - * (1U<<(bfqd->sb_shift - something)), to be robust against
> - * any possible value of bfqd->sb_shift, without having to
> + * (1U + * (1U<<(bt->sb.shift - something)), to be robust against
> + * any possible value of bt->sb.shift, without having to
>* limit 'something'.
>*/
> /* no more than 50% of tags for async I/O */
> - bfqd->word_depths[0][0] = max((1U>1, 1U);
> + bfqd->word_depths[0][0] = max((1U << bt->sb.shift) >> 1, 1U);
> /*
>* no more than 75% of tags for sync writes (25% extra tags
>* w.r.t. async I/O, to prevent async I/O from starving sync
>* writes)
>*/
> - bfqd->word_depths[0][1] = max(((1U>2, 1U);
> + bfqd->word_depths[0][1] = max(((1U << bt->sb.shift) * 3) >> 2, 1U);
>
> /*
>* In-word depths in case some bfq_queue is being weight-
> @@ -5114,9 +5112,9 @@ static void bfq_update_depths(struct bfq_data *bfqd,
> struct sbitmap_queue *bt)
>* shortage.
>*/
> /* no more than ~18% of tags for async I/O */
> - bfqd->word_depths[1][0] = max(((1U>4, 1U);
> + 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>4, 1U);
> + bfqd->word_depths[1][1] = max(((1U << bt->sb.shift) * 6) >> 4, 1U);
> }
>
> static int bfq_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int index)
> diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
> index 8ec7ff92cd6f..faac509cb35e 100644
> --- a/block/bfq-iosched.h
> +++ b/block/bfq-iosched.h
> @@ -636,12 +636,6 @@ struct bfq_data {
> struct bfq_queue *bio_bfqq;
>
> /*
> - * Cached sbitmap shift, used to compute depth limits in
> - * bfq_update_depths.
> - */
> - unsigned int sb_shift;
> -
> - /*
>* Depth limits used in bfq_limit_depth (see comments on the
>* function)
>*/
> --
> 2.7.4
>
