linux-kernel - Re: [PATCH v7 06/13] null_blk: use zone_size_sects

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Message-ID: <4bafa68f-46b3-7a76-de70-377a0f9cf130@opensource.wdc.com>
Date:   Wed, 15 Jun 2022 20:56:23 +0900
From:   Damien Le Moal <damien.lemoal@...nsource.wdc.com>
To:     Pankaj Raghav <p.raghav@...sung.com>, hch@....de,
        snitzer@...hat.com, axboe@...nel.dk
Cc:     bvanassche@....org, linux-kernel@...r.kernel.org,
        jiangbo.365@...edance.com, hare@...e.de, pankydev8@...il.com,
        dm-devel@...hat.com, jonathan.derrick@...ux.dev,
        gost.dev@...sung.com, dsterba@...e.com, jaegeuk@...nel.org,
        linux-nvme@...ts.infradead.org, Johannes.Thumshirn@....com,
        linux-block@...r.kernel.org,
        Damien Le Moal <damien.lemoal@....com>,
        Luis Chamberlain <mcgrof@...nel.org>
Subject: Re: [PATCH v7 06/13] null_blk: use zone_size_sects_shift for power of
 2 zoned devices

On 6/15/22 19:19, Pankaj Raghav wrote:
> Instead of doing is_power_of_2 and ilog2 operation for every IO, cache
> the zone_size_sects_shift variable and use it for power of 2 zoned
> devices.
> 
> This variable will be set to zero for non power of 2 zoned devices.
> 
> Suggested-by: Damien Le Moal <damien.lemoal@....com>
> Reviewed-by: Hannes Reinecke <hare@...e.de>
> Reviewed-by: Luis Chamberlain <mcgrof@...nel.org>
> Signed-off-by: Pankaj Raghav <p.raghav@...sung.com>
> ---
>  drivers/block/null_blk/null_blk.h |  6 ++++++
>  drivers/block/null_blk/zoned.c    | 11 ++++++++---
>  2 files changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/block/null_blk/null_blk.h b/drivers/block/null_blk/null_blk.h
> index 8359b4384..3bc7cbf25 100644
> --- a/drivers/block/null_blk/null_blk.h
> +++ b/drivers/block/null_blk/null_blk.h
> @@ -83,6 +83,12 @@ struct nullb_device {
>  	unsigned int imp_close_zone_no;
>  	struct nullb_zone *zones;
>  	sector_t zone_size_sects;
> +	/*
> +	 * zone_size_sects_shift is only useful when the zone size is
> +	 * power of 2. This variable is set to zero when zone size is non
> +	 * power of 2.
> +	 */
> +	unsigned int zone_size_sects_shift;
>  	bool need_zone_res_mgmt;
>  	spinlock_t zone_res_lock;
>  
> diff --git a/drivers/block/null_blk/zoned.c b/drivers/block/null_blk/zoned.c
> index daf327015..5f929944b 100644
> --- a/drivers/block/null_blk/zoned.c
> +++ b/drivers/block/null_blk/zoned.c
> @@ -16,8 +16,8 @@ static inline sector_t mb_to_sects(unsigned long mb)
>  
>  static inline unsigned int null_zone_no(struct nullb_device *dev, sector_t sect)
>  {
> -	if (is_power_of_2(dev->zone_size_sects))
> -		return sect >> ilog2(dev->zone_size_sects);
> +	if (dev->zone_size_sects_shift)
> +		return sect >> dev->zone_size_sects_shift;
>  
>  	return div64_u64(sect, dev->zone_size_sects);
>  }
> @@ -85,9 +85,14 @@ int null_init_zoned_dev(struct nullb_device *dev, struct request_queue *q)
>  	zone_capacity_sects = mb_to_sects(dev->zone_capacity);
>  	dev_capacity_sects = mb_to_sects(dev->size);
>  	dev->zone_size_sects = mb_to_sects(dev->zone_size);
> +
> +	if (is_power_of_2(dev->zone_size_sects))
> +		dev->zone_size_sects_shift = ilog2(dev->zone_size_sects);
> +	else
> +		dev->zone_size_sects_shift = 0;
> +
>  	dev->nr_zones =	DIV_ROUND_UP_SECTOR_T(dev_capacity_sects,
>  					      dev->zone_size_sects);
> -

white line change.

This patch should be squashed with the previous one.

>  	dev->zones = kvmalloc_array(dev->nr_zones, sizeof(struct nullb_zone),
>  				    GFP_KERNEL | __GFP_ZERO);
>  	if (!dev->zones)


-- 
Damien Le Moal
Western Digital Research