linux-kernel - Re: [PATCH v3 02/10] block: Introduce queue limits for copy-offload support

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Message-ID: <20220217090700.b7n33vbkx5s4qbfq@garbanzo>
Date:   Thu, 17 Feb 2022 01:07:00 -0800
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Nitesh Shetty <nj.shetty@...sung.com>, hch@....de
Cc:     javier@...igon.com, chaitanyak@...dia.com,
        linux-block@...r.kernel.org, linux-scsi@...r.kernel.org,
        dm-devel@...hat.com, linux-nvme@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, axboe@...nel.dk,
        msnitzer@...hat.com, bvanassche@....org,
        martin.petersen@...cle.com, hare@...e.de, kbusch@...nel.org,
        Frederick.Knight@...app.com, osandov@...com,
        lsf-pc@...ts.linux-foundation.org, djwong@...nel.org,
        josef@...icpanda.com, clm@...com, dsterba@...e.com, tytso@....edu,
        jack@...e.com, joshi.k@...sung.com, arnav.dawn@...sung.com,
        nitheshshetty@...il.com, SelvaKumar S <selvakuma.s1@...sung.com>,
        Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        James Smart <james.smart@...adcom.com>,
        Chaitanya Kulkarni <kch@...dia.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 02/10] block: Introduce queue limits for copy-offload
 support

The subject says limits for copy-offload...

On Mon, Feb 14, 2022 at 01:29:52PM +0530, Nitesh Shetty wrote:
> Add device limits as sysfs entries,
>         - copy_offload (RW)
>         - copy_max_bytes (RW)
>         - copy_max_hw_bytes (RO)
>         - copy_max_range_bytes (RW)
>         - copy_max_range_hw_bytes (RO)
>         - copy_max_nr_ranges (RW)
>         - copy_max_nr_ranges_hw (RO)

Some of these seem like generic... and also I see a few more max_hw ones
not listed above...

> --- a/block/blk-settings.c
> +++ b/block/blk-settings.c
> +/**
> + * blk_queue_max_copy_sectors - set max sectors for a single copy payload
> + * @q:  the request queue for the device
> + * @max_copy_sectors: maximum number of sectors to copy
> + **/
> +void blk_queue_max_copy_sectors(struct request_queue *q,
> +		unsigned int max_copy_sectors)
> +{
> +	q->limits.max_hw_copy_sectors = max_copy_sectors;
> +	q->limits.max_copy_sectors = max_copy_sectors;
> +}
> +EXPORT_SYMBOL(blk_queue_max_copy_sectors);

Please use EXPORT_SYMBOL_GPL() for all new things.

Why is this setting both? The documentation does't seem to say.
What's the point?

> +
> +/**
> + * blk_queue_max_copy_range_sectors - set max sectors for a single range, in a copy payload
> + * @q:  the request queue for the device
> + * @max_copy_range_sectors: maximum number of sectors to copy in a single range
> + **/
> +void blk_queue_max_copy_range_sectors(struct request_queue *q,
> +		unsigned int max_copy_range_sectors)
> +{
> +	q->limits.max_hw_copy_range_sectors = max_copy_range_sectors;
> +	q->limits.max_copy_range_sectors = max_copy_range_sectors;
> +}
> +EXPORT_SYMBOL(blk_queue_max_copy_range_sectors);

Same here.

> +/**
> + * blk_queue_max_copy_nr_ranges - set max number of ranges, in a copy payload
> + * @q:  the request queue for the device
> + * @max_copy_nr_ranges: maximum number of ranges
> + **/
> +void blk_queue_max_copy_nr_ranges(struct request_queue *q,
> +		unsigned int max_copy_nr_ranges)
> +{
> +	q->limits.max_hw_copy_nr_ranges = max_copy_nr_ranges;
> +	q->limits.max_copy_nr_ranges = max_copy_nr_ranges;
> +}
> +EXPORT_SYMBOL(blk_queue_max_copy_nr_ranges);

Same.

> +
>  /**
>   * blk_queue_max_write_same_sectors - set max sectors for a single write same
>   * @q:  the request queue for the device
> @@ -541,6 +592,14 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
>  	t->max_segment_size = min_not_zero(t->max_segment_size,
>  					   b->max_segment_size);
>  
> +	t->max_copy_sectors = min(t->max_copy_sectors, b->max_copy_sectors);
> +	t->max_hw_copy_sectors = min(t->max_hw_copy_sectors, b->max_hw_copy_sectors);
> +	t->max_copy_range_sectors = min(t->max_copy_range_sectors, b->max_copy_range_sectors);
> +	t->max_hw_copy_range_sectors = min(t->max_hw_copy_range_sectors,
> +						b->max_hw_copy_range_sectors);
> +	t->max_copy_nr_ranges = min(t->max_copy_nr_ranges, b->max_copy_nr_ranges);
> +	t->max_hw_copy_nr_ranges = min(t->max_hw_copy_nr_ranges, b->max_hw_copy_nr_ranges);
> +
>  	t->misaligned |= b->misaligned;
>  
>  	alignment = queue_limit_alignment_offset(b, start);
> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
> index 9f32882ceb2f..9ddd07f142d9 100644
> --- a/block/blk-sysfs.c
> +++ b/block/blk-sysfs.c
> @@ -212,6 +212,129 @@ static ssize_t queue_discard_zeroes_data_show(struct request_queue *q, char *pag
>  	return queue_var_show(0, page);
>  }
>  
> +static ssize_t queue_copy_offload_show(struct request_queue *q, char *page)
> +{
> +	return queue_var_show(blk_queue_copy(q), page);
> +}
> +
> +static ssize_t queue_copy_offload_store(struct request_queue *q,
> +				       const char *page, size_t count)
> +{
> +	unsigned long copy_offload;
> +	ssize_t ret = queue_var_store(&copy_offload, page, count);
> +
> +	if (ret < 0)
> +		return ret;
> +
> +	if (copy_offload && !q->limits.max_hw_copy_sectors)
> +		return -EINVAL;


If the kernel schedules, copy_offload may still be true and
max_hw_copy_sectors may be set to 0. Is that an issue?

> +
> +	if (copy_offload)
> +		blk_queue_flag_set(QUEUE_FLAG_COPY, q);
> +	else
> +		blk_queue_flag_clear(QUEUE_FLAG_COPY, q);

The flag may be set but the queue flag could be set. Is that an issue?

> @@ -597,6 +720,14 @@ QUEUE_RO_ENTRY(queue_nr_zones, "nr_zones");
>  QUEUE_RO_ENTRY(queue_max_open_zones, "max_open_zones");
>  QUEUE_RO_ENTRY(queue_max_active_zones, "max_active_zones");
>  
> +QUEUE_RW_ENTRY(queue_copy_offload, "copy_offload");
> +QUEUE_RO_ENTRY(queue_copy_max_hw, "copy_max_hw_bytes");
> +QUEUE_RW_ENTRY(queue_copy_max, "copy_max_bytes");
> +QUEUE_RO_ENTRY(queue_copy_range_max_hw, "copy_max_range_hw_bytes");
> +QUEUE_RW_ENTRY(queue_copy_range_max, "copy_max_range_bytes");
> +QUEUE_RO_ENTRY(queue_copy_nr_ranges_max_hw, "copy_max_nr_ranges_hw");
> +QUEUE_RW_ENTRY(queue_copy_nr_ranges_max, "copy_max_nr_ranges");

Seems like you need to update Documentation/ABI/stable/sysfs-block.

> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index efed3820cbf7..792e6d556589 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -254,6 +254,13 @@ struct queue_limits {
>  	unsigned int		discard_alignment;
>  	unsigned int		zone_write_granularity;
>  
> +	unsigned long		max_hw_copy_sectors;
> +	unsigned long		max_copy_sectors;
> +	unsigned int		max_hw_copy_range_sectors;
> +	unsigned int		max_copy_range_sectors;
> +	unsigned short		max_hw_copy_nr_ranges;
> +	unsigned short		max_copy_nr_ranges;

Before limits start growing more.. I wonder if we should just
stuff hw offload stuff to its own struct within queue_limits.

Christoph?

  Luis