Re: [PATCH V2 4/8] block: null_blk: introduce module parameter of 'g_global_tags'

[Omar Sandoval <osandov@osandov.com>]

On Mon, Feb 05, 2018 at 11:20:31PM +0800, Ming Lei wrote:
> This patch introduces the parameter of 'g_global_tags' so that we can
> test this feature by null_blk easiy.
> 
> Not see obvious performance drop with global_tags when the whole hw
> depth is kept as same:
> 
> 1) no 'global_tags', each hw queue depth is 1, and 4 hw queues
> modprobe null_blk queue_mode=2 nr_devices=4 shared_tags=1 global_tags=0 submit_queues=4 hw_queue_depth=1
> 
> 2) 'global_tags', global hw queue depth is 4, and 4 hw queues
> modprobe null_blk queue_mode=2 nr_devices=4 shared_tags=1 global_tags=1 submit_queues=4 hw_queue_depth=4
> 
> 3) fio test done in above two settings:
>    fio --bs=4k --size=512G  --rw=randread --norandommap --direct=1 --ioengine=libaio --iodepth=4 --runtime=$RUNTIME --group_reporting=1  --name=nullb0 --filename=/dev/nullb0 --name=nullb1 --filename=/dev/nullb1 --name=nullb2 --filename=/dev/nullb2 --name=nullb3 --filename=/dev/nullb3
> 
> 1M IOPS can be reached in both above tests which is done in one VM.
> 
> Cc: Arun Easi <arun.easi@cavium.com>
> Cc: Omar Sandoval <osandov@fb.com>,
> Cc: "Martin K. Petersen" <martin.petersen@oracle.com>,
> Cc: James Bottomley <james.bottomley@hansenpartnership.com>,
> Cc: Christoph Hellwig <hch@lst.de>,
> Cc: Don Brace <don.brace@microsemi.com>
> Cc: Kashyap Desai <kashyap.desai@broadcom.com>
> Cc: Peter Rivera <peter.rivera@broadcom.com>
> Cc: Mike Snitzer <snitzer@redhat.com>
> Tested-by: Laurence Oberman <loberman@redhat.com>
> Reviewed-by: Hannes Reinecke <hare@suse.de>

The module parameter is just called "global_tags", not "g_global_tags",
right? The subject should say the former.

Otherwise,

Reviewed-by: Omar Sandoval <osandov@fb.com>

> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
>  drivers/block/null_blk.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/block/null_blk.c b/drivers/block/null_blk.c
> index 287a09611c0f..ad0834efad42 100644
> --- a/drivers/block/null_blk.c
> +++ b/drivers/block/null_blk.c
> @@ -163,6 +163,10 @@ static int g_submit_queues = 1;
>  module_param_named(submit_queues, g_submit_queues, int, S_IRUGO);
>  MODULE_PARM_DESC(submit_queues, "Number of submission queues");
>  
> +static int g_global_tags = 0;
> +module_param_named(global_tags, g_global_tags, int, S_IRUGO);
> +MODULE_PARM_DESC(global_tags, "All submission queues share one tags");
> +
>  static int g_home_node = NUMA_NO_NODE;
>  module_param_named(home_node, g_home_node, int, S_IRUGO);
>  MODULE_PARM_DESC(home_node, "Home node for the device");
> @@ -1622,6 +1626,8 @@ static int null_init_tag_set(struct nullb *nullb, struct blk_mq_tag_set *set)
>  	set->flags = BLK_MQ_F_SHOULD_MERGE;
>  	if (g_no_sched)
>  		set->flags |= BLK_MQ_F_NO_SCHED;
> +	if (g_global_tags)
> +		set->flags |= BLK_MQ_F_GLOBAL_TAGS;
>  	set->driver_data = NULL;
>  
>  	if ((nullb && nullb->dev->blocking) || g_blocking)
> -- 
> 2.9.5
>