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Date:   Wed, 29 Mar 2023 16:11:42 +0530
From:   Nitesh Shetty <nj.shetty@samsung.com>
To:     Damien Le Moal <damien.lemoal@opensource.wdc.com>
Cc:     Anuj Gupta <anuj20.g@samsung.com>, Jens Axboe <axboe@kernel.dk>,
        Alasdair Kergon <agk@redhat.com>,
        Mike Snitzer <snitzer@kernel.org>, dm-devel@redhat.com,
        Keith Busch <kbusch@kernel.org>,
        Christoph Hellwig <hch@lst.de>,
        Sagi Grimberg <sagi@grimberg.me>,
        James Smart <james.smart@broadcom.com>,
        Chaitanya Kulkarni <kch@nvidia.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
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        nitheshshetty@gmail.com, gost.dev@samsung.com,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
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Subject: Re: [PATCH v8 1/9] block: Introduce queue limits for copy-offload
 support
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On Wed, Mar 29, 2023 at 05:40:09PM +0900, Damien Le Moal wrote:
> On 3/27/23 17:40, Anuj Gupta wrote:
> > From: Nitesh Shetty <nj.shetty@samsung.com>
> > 
> > Add device limits as sysfs entries,
> >         - copy_offload (RW)
> >         - copy_max_bytes (RW)
> >         - copy_max_bytes_hw (RO)
> > 
> > Above limits help to split the copy payload in block layer.
> > copy_offload: used for setting copy offload(1) or emulation(0).
> > copy_max_bytes: maximum total length of copy in single payload.
> > copy_max_bytes_hw: Reflects the device supported maximum limit.
> > 
> > Reviewed-by: Hannes Reinecke <hare@suse.de>
> > Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
> > Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
> > Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
> > ---
> >  Documentation/ABI/stable/sysfs-block | 36 ++++++++++++++++
> >  block/blk-settings.c                 | 24 +++++++++++
> >  block/blk-sysfs.c                    | 64 ++++++++++++++++++++++++++++
> >  include/linux/blkdev.h               | 12 ++++++
> >  include/uapi/linux/fs.h              |  3 ++
> >  5 files changed, 139 insertions(+)
> > 
> > diff --git a/Documentation/ABI/stable/sysfs-block b/Documentation/ABI/stable/sysfs-block
> > index c57e5b7cb532..f5c56ad91ad6 100644
> > --- a/Documentation/ABI/stable/sysfs-block
> > +++ b/Documentation/ABI/stable/sysfs-block
> > @@ -155,6 +155,42 @@ Description:
> >  		last zone of the device which may be smaller.
> >  
> >  
> > +What:		/sys/block/<disk>/queue/copy_offload
> > +Date:		November 2022
> > +Contact:	linux-block@vger.kernel.org
> > +Description:
> > +		[RW] When read, this file shows whether offloading copy to
> > +		device is enabled (1) or disabled (0). Writing '0' to this
> 
> ...to a device...
> 
acked

> > +		file will disable offloading copies for this device.
> > +		Writing any '1' value will enable this feature. If device
> 
> If the device does...
> 
acked

> > +		does not support offloading, then writing 1, will result in
> > +		error.
> > +
> > +
> > +What:		/sys/block/<disk>/queue/copy_max_bytes
> > +Date:		November 2022
> > +Contact:	linux-block@vger.kernel.org
> > +Description:
> > +		[RW] While 'copy_max_bytes_hw' is the hardware limit for the
> > +		device, 'copy_max_bytes' setting is the software limit.
> > +		Setting this value lower will make Linux issue smaller size
> > +		copies from block layer.
> 
> 		This is the maximum number of bytes that the block
>                 layer will allow for a copy request. Must be smaller than
>                 or equal to the maximum size allowed by the hardware indicated

Looks good.  Will update in next version. We took reference from discard. 

> 		by copy_max_bytes_hw. Write 0 to use the default kernel
> 		settings.
> 

Nack, writing 0 will not set it to default value. (default value is
copy_max_bytes = copy_max_bytes_hw)

> > +
> > +
> > +What:		/sys/block/<disk>/queue/copy_max_bytes_hw
> > +Date:		November 2022
> > +Contact:	linux-block@vger.kernel.org
> > +Description:
> > +		[RO] Devices that support offloading copy functionality may have
> > +		internal limits on the number of bytes that can be offloaded
> > +		in a single operation. The `copy_max_bytes_hw`
> > +		parameter is set by the device driver to the maximum number of
> > +		bytes that can be copied in a single operation. Copy
> > +		requests issued to the device must not exceed this limit.
> > +		A value of 0 means that the device does not
> > +		support copy offload.
> 
> 		[RO] This is the maximum number of kilobytes supported in a
>                 single data copy offload operation. A value of 0 means that the
> 		device does not support copy offload.
> 

Nack, value is in bytes. Same as discard.

> > +
> > +
> >  What:		/sys/block/<disk>/queue/crypto/
> >  Date:		February 2022
> >  Contact:	linux-block@vger.kernel.org
> > diff --git a/block/blk-settings.c b/block/blk-settings.c
> > index 896b4654ab00..350f3584f691 100644
> > --- a/block/blk-settings.c
> > +++ b/block/blk-settings.c
> > @@ -59,6 +59,8 @@ void blk_set_default_limits(struct queue_limits *lim)
> >  	lim->zoned = BLK_ZONED_NONE;
> >  	lim->zone_write_granularity = 0;
> >  	lim->dma_alignment = 511;
> > +	lim->max_copy_sectors_hw = 0;
> > +	lim->max_copy_sectors = 0;
> >  }
> >  
> >  /**
> > @@ -82,6 +84,8 @@ void blk_set_stacking_limits(struct queue_limits *lim)
> >  	lim->max_dev_sectors = UINT_MAX;
> >  	lim->max_write_zeroes_sectors = UINT_MAX;
> >  	lim->max_zone_append_sectors = UINT_MAX;
> > +	lim->max_copy_sectors_hw = ULONG_MAX;
> > +	lim->max_copy_sectors = ULONG_MAX;
> >  }
> >  EXPORT_SYMBOL(blk_set_stacking_limits);
> >  
> > @@ -183,6 +187,22 @@ void blk_queue_max_discard_sectors(struct request_queue *q,
> >  }
> >  EXPORT_SYMBOL(blk_queue_max_discard_sectors);
> >  
> > +/**
> > + * blk_queue_max_copy_sectors_hw - 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_hw(struct request_queue *q,
> > +		unsigned int max_copy_sectors)
> > +{
> > +	if (max_copy_sectors >= MAX_COPY_TOTAL_LENGTH)
> 
> Confusing name as LENGTH may be interpreted as bytes. MAX_COPY_SECTORS would be
> better.
> 

Agreed, we will make MAX_COPY_TOTAL_LENGTH explicit to bytes.
We also check this limit against user payload length which is in bytes(patch 2).
So there is a inconsistency from our end (patch 1 and 2). We will fix this
in next version.

> > +		max_copy_sectors = MAX_COPY_TOTAL_LENGTH;
> > +
> > +	q->limits.max_copy_sectors_hw = max_copy_sectors;
> > +	q->limits.max_copy_sectors = max_copy_sectors;
> > +}
> > +EXPORT_SYMBOL_GPL(blk_queue_max_copy_sectors_hw);
> 
> 
> -- 
> Damien Le Moal
> Western Digital Research
> 
> 

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