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

[Chaitanya Kulkarni <chaitanyak@nvidia.com>]

On 2/17/22 1:07 AM, 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...
> 
>> --- 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?
> 

Potentially use a pointer to structure and maybe make it configurable,
although I'm not sure about the later part, I'll let Christoph decide
that.

>    Luis
> 

-ck