Re: [PATCH v8 1/9] block: Introduce queue limits for copy-offload support

Nitesh Shetty
2023-03-29T11:10:50Z

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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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