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Message-ID: <3d387876-342d-1516-92aa-24d39aa3f95c@suse.de>
Date:   Tue, 24 May 2022 07:22:48 +0200
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Subject: Re: [PATCH v5 6/7] null_blk: use zone_size_sects_shift for power of 2
 zoned devices
Content-Language: en-US
To:     Pankaj Raghav <p.raghav@samsung.com>, axboe@kernel.dk, hch@lst.de,
        snitzer@redhat.com, damien.lemoal@opensource.wdc.com,
        Johannes.Thumshirn@wdc.com
Cc:     linux-nvme@lists.infradead.org, dm-devel@redhat.com,
        dsterba@suse.com, jiangbo.365@bytedance.com,
        linux-kernel@vger.kernel.org, gost.dev@samsung.com,
        linux-block@vger.kernel.org, jaegeuk@kernel.org,
        Damien Le Moal <damien.lemoal@wdc.com>
References: <20220523161601.58078-1-p.raghav@samsung.com>
 <CGME20220523161612eucas1p102a76ba431c934230309042521018915@eucas1p1.samsung.com>
 <20220523161601.58078-7-p.raghav@samsung.com>
From:   Hannes Reinecke <hare@suse.de>
In-Reply-To: <20220523161601.58078-7-p.raghav@samsung.com>
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Precedence: bulk

On 5/23/22 18:16, 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@wdc.com>
> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
> ---
>   drivers/block/null_blk/null_blk.h |  6 ++++++
>   drivers/block/null_blk/zoned.c    | 10 ++++++++--
>   2 files changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/block/null_blk/null_blk.h b/drivers/block/null_blk/null_blk.h
> index 78eb56b0ca55..3d6e41a9491f 100644
> --- a/drivers/block/null_blk/null_blk.h
> +++ b/drivers/block/null_blk/null_blk.h
> @@ -74,6 +74,12 @@ 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 00c34e65ef0a..806bef98ac83 100644
> --- a/drivers/block/null_blk/zoned.c
> +++ b/drivers/block/null_blk/zoned.c
> @@ -13,8 +13,8 @@ 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);
>   }
> @@ -82,6 +82,12 @@ 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 =
>   		div64_u64(roundup(dev_capacity_sects, dev->zone_size_sects),
>   			  dev->zone_size_sects);
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
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