Re: [PATCH 4/9] bfq-iosched: remove unused variable

[Omar Sandoval <osandov@osandov.com>]

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 <paolo.valente@linaro.org>

Reviewed-by: Omar Sandoval <osandov@fb.com>

> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> ---
>  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<<bfqd->sb_shift), instead of computing directly
> -	 * (1U<<(bfqd->sb_shift - something)), to be robust against
> -	 * any possible value of bfqd->sb_shift, without having to
> +	 * (1U<<bt->sb.shift), instead of computing directly
> +	 * (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<<bfqd->sb_shift)>>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<<bfqd->sb_shift) * 3)>>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<<bfqd->sb_shift) * 3)>>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<<bfqd->sb_shift) * 6)>>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
>