The function blk_mq_update_nr_hw_queues in nbd_start_device may causes a queue freeze. The previous commit addressed this issue for newly created nbd device via setting the expected nr_hw_queues in nbd_dev_add. However, when reusing an old inactive nbd device, the queue freeze can still occur when old nbd->tag_set->nr_hw_queues not match the new socket connection count. Inactive nbd devices can originate from two sources: loading the nbd module with nbds_max, which sets the default nr_hw_queues to 1, and the netlink method, which sets nr_hw_queues according to the expected number of socket connections. For the first case, we can add a module parameter to allow changing the default nr_hw_queues. This way, users who know their expected number of connections can prevent queue freezes on pre-created devices via nbds_max. Before this patchset: real 0m2.195s user 0m0.005s sys 0m0.022s After this patchset: real 0m0.090s user 0m0.004s sys 0m0.018s Signed-off-by: Yang Erkun --- drivers/block/nbd.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c index 2bb98e41b99b..1d8cdc5713eb 100644 --- a/drivers/block/nbd.c +++ b/drivers/block/nbd.c @@ -166,6 +166,7 @@ static struct dentry *nbd_dbg_dir; static unsigned int nbds_max = 16; static int max_part = 16; +static int nr_hw_queues = 1; static int part_shift; static int nbd_dev_dbg_init(struct nbd_device *nbd); @@ -2733,8 +2734,10 @@ static int __init nbd_init(void) } nbd_dbg_init(); + if (nr_hw_queues < 1) + nr_hw_queues = 1; for (i = 0; i < nbds_max; i++) - nbd_dev_add(i, 1, 1); + nbd_dev_add(i, 1, nr_hw_queues); return 0; } @@ -2795,3 +2798,6 @@ module_param(nbds_max, int, 0444); MODULE_PARM_DESC(nbds_max, "number of network block devices to initialize (default: 16)"); module_param(max_part, int, 0444); MODULE_PARM_DESC(max_part, "number of partitions per device (default: 16)"); +module_param(nr_hw_queues, int, 0444); +MODULE_PARM_DESC(nr_hw_queues, +"number of hardware queues for devices pre-created at module load (default: 1). "); -- 2.52.0