linux-kernel - Re: [PATCH v2 24/35] block: null_blk: fix opencoded find_and_set_bit() in get

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Message-ID: <ef07f915-e598-402e-bb2b-011bb0aebd7f@bytedance.com>
Date:   Tue, 5 Dec 2023 10:39:29 +0800
From:   Chengming Zhou <zhouchengming@...edance.com>
To:     Yury Norov <yury.norov@...il.com>, linux-kernel@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>,
        Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        Chaitanya Kulkarni <kch@...dia.com>,
        Ming Lei <ming.lei@...hat.com>,
        Johannes Thumshirn <johannes.thumshirn@....com>,
        Nitesh Shetty <nj.shetty@...sung.com>,
        Akinobu Mita <akinobu.mita@...il.com>,
        Shin'ichiro Kawasaki <shinichiro.kawasaki@....com>,
        linux-block@...r.kernel.org
Cc:     Jan Kara <jack@...e.cz>,
        Mirsad Todorovac <mirsad.todorovac@....unizg.hr>,
        Matthew Wilcox <willy@...radead.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Maxim Kuvyrkov <maxim.kuvyrkov@...aro.org>,
        Alexey Klimov <klimov.linux@...il.com>,
        Bart Van Assche <bvanassche@....org>,
        Sergey Shtylyov <s.shtylyov@....ru>
Subject: Re: [PATCH v2 24/35] block: null_blk: fix opencoded
 find_and_set_bit() in get_tag()

On 2023/12/4 03:32, Yury Norov wrote:
> get_tag() opencodes find_and_set_bit(). Switch the code to use the
> dedicated function, and get rid of get_tag entirely.
> 
> Signed-off-by: Yury Norov <yury.norov@...il.com>

Looks good to me!

Reviewed-by: Chengming Zhou <zhouchengming@...edance.com>

> ---
>  drivers/block/null_blk/main.c | 41 +++++++++++------------------------
>  1 file changed, 13 insertions(+), 28 deletions(-)
> 
> diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
> index 3021d58ca51c..671dbb9ab928 100644
> --- a/drivers/block/null_blk/main.c
> +++ b/drivers/block/null_blk/main.c
> @@ -760,19 +760,6 @@ static void put_tag(struct nullb_queue *nq, unsigned int tag)
>  		wake_up(&nq->wait);
>  }
>  
> -static unsigned int get_tag(struct nullb_queue *nq)
> -{
> -	unsigned int tag;
> -
> -	do {
> -		tag = find_first_zero_bit(nq->tag_map, nq->queue_depth);
> -		if (tag >= nq->queue_depth)
> -			return -1U;
> -	} while (test_and_set_bit_lock(tag, nq->tag_map));
> -
> -	return tag;
> -}
> -
>  static void free_cmd(struct nullb_cmd *cmd)
>  {
>  	put_tag(cmd->nq, cmd->tag);
> @@ -782,24 +769,22 @@ static enum hrtimer_restart null_cmd_timer_expired(struct hrtimer *timer);
>  
>  static struct nullb_cmd *__alloc_cmd(struct nullb_queue *nq)
>  {
> +	unsigned int tag = find_and_set_bit_lock(nq->tag_map, nq->queue_depth);
>  	struct nullb_cmd *cmd;
> -	unsigned int tag;
> -
> -	tag = get_tag(nq);
> -	if (tag != -1U) {
> -		cmd = &nq->cmds[tag];
> -		cmd->tag = tag;
> -		cmd->error = BLK_STS_OK;
> -		cmd->nq = nq;
> -		if (nq->dev->irqmode == NULL_IRQ_TIMER) {
> -			hrtimer_init(&cmd->timer, CLOCK_MONOTONIC,
> -				     HRTIMER_MODE_REL);
> -			cmd->timer.function = null_cmd_timer_expired;
> -		}
> -		return cmd;
> +
> +	if (tag >= nq->queue_depth)
> +		return NULL;
> +
> +	cmd = &nq->cmds[tag];
> +	cmd->tag = tag;
> +	cmd->error = BLK_STS_OK;
> +	cmd->nq = nq;
> +	if (nq->dev->irqmode == NULL_IRQ_TIMER) {
> +		hrtimer_init(&cmd->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> +		cmd->timer.function = null_cmd_timer_expired;
>  	}
>  
> -	return NULL;
> +	return cmd;
>  }
>  
>  static struct nullb_cmd *alloc_cmd(struct nullb_queue *nq, struct bio *bio)