Re: [PATCH 1/1] null_blk: add option for managing virtual boundary

[Damien Le Moal <Damien.LeMoal@wdc.com>]

On 2021/04/12 1:30, Max Gurtovoy wrote:
> This will enable changing the virtual boundary of null blk devices. For
> now, null blk devices didn't have any restriction on the scatter/gather
> elements received from the block layer. Add a module parameter that will
> control the virtual boundary. This will enable testing the efficiency of
> the block layer bounce buffer in case a suitable application will send
> discontiguous IO to the given device.
> 
> Initial testing with patched FIO showed the following results (64 jobs,
> 128 iodepth):
> IO size      READ (virt=false)   READ (virt=true)   Write (virt=false)  Write (virt=true)
> ----------  ------------------- -----------------  ------------------- -------------------
>  1k            10.7M                8482k               10.8M              8471k
>  2k            10.4M                8266k               10.4M              8271k
>  4k            10.4M                8274k               10.3M              8226k
>  8k            10.2M                8131k               9800k              7933k
>  16k           9567k                7764k               8081k              6828k
>  32k           8865k                7309k               5570k              5153k
>  64k           7695k                6586k               2682k              2617k
>  128k          5346k                5489k               1320k              1296k
> 
> Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> ---
>  drivers/block/null_blk/main.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
> index d6c821d48090..9ca80e38f7e5 100644
> --- a/drivers/block/null_blk/main.c
> +++ b/drivers/block/null_blk/main.c
> @@ -84,6 +84,10 @@ enum {
>  	NULL_Q_MQ		= 2,
>  };
>  
> +static bool g_virt_boundary = false;
> +module_param_named(virt_boundary, g_virt_boundary, bool, 0444);
> +MODULE_PARM_DESC(virt_boundary, "Require a virtual boundary for the device. Default: False");
> +
>  static int g_no_sched;
>  module_param_named(no_sched, g_no_sched, int, 0444);
>  MODULE_PARM_DESC(no_sched, "No io scheduler");
> @@ -1880,6 +1884,9 @@ static int null_add_dev(struct nullb_device *dev)
>  				 BLK_DEF_MAX_SECTORS);
>  	blk_queue_max_hw_sectors(nullb->q, dev->max_sectors);
>  
> +	if (g_virt_boundary)
> +		blk_queue_virt_boundary(nullb->q, PAGE_SIZE - 1);
> +
>  	null_config_discard(nullb);
>  
>  	sprintf(nullb->disk_name, "nullb%d", nullb->index);
> 

Looks good to me, but could you also add the configfs equivalent setting ?


-- 
Damien Le Moal
Western Digital Research