[PATCH V3 6/8] block: null_blk: introduce module parameter of 'g_host_tags'

Ming Lei
2018-02-27T10:07:48Z

This patch introduces the parameter of 'g_host_tags' so that we can
test this feature by null_blk easiy.

With host_tags when the whole hw depth is kept as same, it is observed
that IOPS can be improved by ~50% on a dual socket(total 16 CPU cores)
system:

1) no 'host_tags', each 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

IOPS: 1382K

2) 'host_tags', each hw queue depth is 8, and 2 hw queues
modprobe null_blk queue_mode=2 nr_devices=4 shared_tags=1 host_tags=1 submit_queues=2 hw_queue_depth=16

IOPS: 2124K

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

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: Laurence Oberman <loberman@redhat.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Mike Snitzer <snitzer@redhat.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..51b16249028a 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_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, 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_host_tags)
+ set->flags |= BLK_MQ_F_HOST_TAGS;
set->driver_data = NULL;

if ((nullb && nullb->dev->blocking) || g_blocking)
--
2.9.5