Re: [PATCH v5 8/8] nbd: add nr_hw_queues module parameter for pre-created devices

[yangerkun <yangerkun@huawei.com>]

在 2026/8/2 20:21, yu kuai 写道:
> Hi,
> 
> 在 2026/7/30 16:20, Yang Erkun 写道:
>> 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 <yangerkun@huawei.com>
>> ---
>>    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 6369a409e10c..2194c7d7b2ea 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);
>> @@ -2740,8 +2741,10 @@ 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);
> 
> I still feel the module param name nr_hw_queues really confusing. How about rename it like
> pre_defined_connections? And add comments here that user should config the exact number of
> connections to avoid queue freeze from nbd_start_device().

OK, will do it next version. Thanks a lot for your review for this series!

> 
>>    	return 0;
>>    }
>>    
>> @@ -2802,3 +2805,6 @@ 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). ");
>