Re: [PATCH 2/9] block: null_blk: introduce module parameter of 'g_host_tags'

From: Minwoo Im <minwoo.im.dev@gmail.com>
To: Ming Lei <ming.lei@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>,
	linux-block@vger.kernel.org, linux-scsi@vger.kernel.org,
	"Martin K . Petersen" <martin.petersen@oracle.com>,
	James Bottomley <James.Bottomley@HansenPartnership.com>,
	Bart Van Assche <bvanassche@acm.org>,
	Hannes Reinecke <hare@suse.com>,
	John Garry <john.garry@huawei.com>,
	Don Brace <don.brace@microsemi.com>,
	Kashyap Desai <kashyap.desai@broadcom.com>,
	Sathya Prakash <sathya.prakash@broadcom.com>,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH 2/9] block: null_blk: introduce module parameter of 'g_host_tags'
Date: Sun, 2 Jun 2019 10:56:16 +0900	[thread overview]
Message-ID: <20190602015615.GB28933@minwooim-desktop> (raw)
In-Reply-To: <20190531022801.10003-3-ming.lei@redhat.com>

On 19-05-31 10:27:54, Ming Lei wrote:
> Introduces parameter of 'g_host_tags' for testing hostwide tags.
> 
> Not observe performance drop in the following test:
> 
> 1) no 'host_tags', hw queue depth is 16, and 1 hw queue
> modprobe null_blk queue_mode=2 nr_devices=4 shared_tags=1 host_tags=0 submit_queues=1 hw_queue_depth=16
> 
> 2) 'host_tags', global hw queue depth is 16, and 8 hw queues
> modprobe null_blk queue_mode=2 nr_devices=4 shared_tags=1 host_tags=1 submit_queues=8 hw_queue_depth=16
> 
> 3) fio test command:
> 
> fio --bs=4k --ioengine=libaio --iodepth=16 --filename=/dev/nullb0:/dev/nullb1:/dev/nullb2:/dev/nullb3 --direct=1 --runtime=30 --numjobs=16 --rw=randread --name=test --group_reporting --gtod_reduce=1
> 
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
>  drivers/block/null_blk_main.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/block/null_blk_main.c b/drivers/block/null_blk_main.c
> index 447d635c79a2..3c04446f3649 100644
> --- a/drivers/block/null_blk_main.c
> +++ b/drivers/block/null_blk_main.c
> @@ -91,6 +91,10 @@ static int g_submit_queues = 1;
>  module_param_named(submit_queues, g_submit_queues, int, 0444);
>  MODULE_PARM_DESC(submit_queues, "Number of submission queues");
>  
> +static int g_host_tags = 0;
> +module_param_named(host_tags, g_host_tags, int, S_IRUGO);
> +MODULE_PARM_DESC(host_tags, "All submission queues share one tags");
> +
>  static int g_home_node = NUMA_NO_NODE;
>  module_param_named(home_node, g_home_node, int, 0444);
>  MODULE_PARM_DESC(home_node, "Home node for the device");
> @@ -1554,6 +1558,8 @@ 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_host_tags)
> +		set->flags |= BLK_MQ_F_HOST_TAGS;

Hi Ming,

I think it would be great if you can provide documentation update also
for the null_blk (Documenation/block/null_blk.txt).  Also what Bart has
pointed out can be applied, I guess.

Otherwise, it looks good to me.

Reviewed-by: Minwoo Im <minwoo.im.dev@gmail.com>