linux-kernel - Re: [PATCH RESEND v2 10/10] block, bfq: remove check of bfq_wr_max_softrt

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Date:   Mon, 2 Jan 2023 17:05:05 +0100
From:   Jan Kara <jack@...e.cz>
To:     Kemeng Shi <shikemeng@...weicloud.com>
Cc:     paolo.valente@...aro.org, axboe@...nel.dk,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        jack@...e.cz, hch@....de, damien.lemoal@....com
Subject: Re: [PATCH RESEND v2 10/10] block, bfq: remove check of
 bfq_wr_max_softrt_rate which is always greater than 0

On Fri 23-12-22 03:16:41, Kemeng Shi wrote:
> bfqd->bfq_wr_max_softrt_rate is assigned with 7000 in bfq_init_queue and
> never changed. So we can remove bfqd->bfq_wr_max_softrt_rate > 0 check
> which is always true.
> 
> Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>

I would just leave these checks for documentation purposes and for possible
experiments (e.g. disabling this logic by setting bfq_wr_max_softrt_rate to
0). Alternatively, we could just define a constant for this and
then we can remove all the checks, that would be a clean solution as well.

								Honza

> ---
>  block/bfq-iosched.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
> index 91bc68fba72d..00cdd42ac02a 100644
> --- a/block/bfq-iosched.c
> +++ b/block/bfq-iosched.c
> @@ -1788,8 +1788,7 @@ static void bfq_bfqq_handle_idle_busy_switch(struct bfq_data *bfqd,
>  	 *   to control its weight explicitly)
>  	 */
>  	in_burst = bfq_bfqq_in_large_burst(bfqq);
> -	soft_rt = bfqd->bfq_wr_max_softrt_rate > 0 &&
> -		!BFQQ_TOTALLY_SEEKY(bfqq) &&
> +	soft_rt = !BFQQ_TOTALLY_SEEKY(bfqq) &&
>  		!in_burst &&
>  		time_is_before_jiffies(bfqq->soft_rt_next_start) &&
>  		bfqq->dispatched == 0 &&
> @@ -4284,8 +4283,7 @@ void bfq_bfqq_expire(struct bfq_data *bfqd,
>  	if (bfqd->low_latency && bfqq->wr_coeff == 1)
>  		bfqq->last_wr_start_finish = jiffies;
>  
> -	if (bfqd->low_latency && bfqd->bfq_wr_max_softrt_rate > 0 &&
> -	    RB_EMPTY_ROOT(&bfqq->sort_list)) {
> +	if (bfqd->low_latency && RB_EMPTY_ROOT(&bfqq->sort_list)) {
>  		/*
>  		 * If we get here, and there are no outstanding
>  		 * requests, then the request pattern is isochronous
> -- 
> 2.30.0
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR