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Date:   Thu, 17 Feb 2022 18:29:01 +0530
From:   Nitesh Shetty <nj.shetty@samsung.com>
To:     Luis Chamberlain <mcgrof@kernel.org>
Cc:     hch@lst.de, javier@javigon.com, chaitanyak@nvidia.com,
        linux-block@vger.kernel.org, linux-scsi@vger.kernel.org,
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        jack@suse.com, joshi.k@samsung.com, arnav.dawn@samsung.com,
        nitheshshetty@gmail.com, SelvaKumar S <selvakuma.s1@samsung.com>,
        Alasdair Kergon <agk@redhat.com>,
        Mike Snitzer <snitzer@redhat.com>,
        Sagi Grimberg <sagi@grimberg.me>,
        James Smart <james.smart@broadcom.com>,
        Chaitanya Kulkarni <kch@nvidia.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 02/10] block: Introduce queue limits for copy-offload
 support
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 Thu, Feb 17, 2022 at 01:07:00AM -0800, Luis Chamberlain wrote:
> 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...
>
queue_limits and sysfs entries are differently named.
All sysfs entries start with copy_* prefix. Also it makes easy to lookup
all copy sysfs.
For queue limits naming, I tried to following existing queue limit
convention (like discard).

> > --- 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.
> 
acked.

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

This function is used only by driver, while intializing request queue.
I will put this as part of description next time.

> > +
> > +/**
> > + * 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?
>

This check ensures that, we dont enable offload if device doesnt support
offload. I feel it shouldn't be 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.
>

acked. 

> > 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
>
Yeah, would like to know community opinion on this.


-- Nitesh

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