Re: [PATCH v3 1/1] virtio-blk: add num_request_queues module parameter

[Max Gurtovoy <mgurtovoy@nvidia.com>]

On 9/5/2021 4:10 PM, Leon Romanovsky wrote:
> On Sun, Sep 05, 2021 at 02:16:58PM +0300, Max Gurtovoy wrote:
>> On 9/5/2021 1:19 PM, Leon Romanovsky wrote:
>>> On Sun, Sep 05, 2021 at 12:19:09PM +0300, Max Gurtovoy wrote:
>>>> On 9/5/2021 11:49 AM, Chaitanya Kulkarni wrote:
>>>>> On 9/5/2021 12:46 AM, Leon Romanovsky wrote:
>>>>>>> +static unsigned int num_request_queues;
>>>>>>> +module_param_cb(num_request_queues, &queue_count_ops,
>>>>>>> &num_request_queues,
>>>>>>> +        0644);
>>>>>>> +MODULE_PARM_DESC(num_request_queues,
>>>>>>> +         "Number of request queues to use for blk device.
>>>>>>> Should > 0");
>>>>>>> +
>>>>>> Won't it limit all virtio block devices to the same limit?
>>>>>>
>>>>>> It is very common to see multiple virtio-blk devices on the same system
>>>>>> and they probably need different limits.
>>>>>>
>>>>>> Thanks
>>>>> Without looking into the code, that can be done adding a configfs
>>>>>
>>>>> interface and overriding a global value (module param) when it is set
>>>>> from
>>>>>
>>>>> configfs.
>>>>>
>>>>>
>>>> You have many ways to overcome this issue.
>>>>
>>>> For example:
>>>>
>>>> # ls -l /sys/block/vda/mq/
>>>> drwxr-xr-x 18 root root 0 Sep  5 12:14 0
>>>> drwxr-xr-x 18 root root 0 Sep  5 12:14 1
>>>> drwxr-xr-x 18 root root 0 Sep  5 12:14 2
>>>> drwxr-xr-x 18 root root 0 Sep  5 12:14 3
>>>>
>>>> # echo virtio0 > /sys/bus/virtio/drivers/virtio_blk/unbind
>>>>
>>>> # echo 8 > /sys/module/virtio_blk/parameters/num_request_queues
>>> This is global to all virtio-blk devices.
>> You define a global module param but you bind/unbind a specific device.
>>
>> Do you have a better way to control it ?
> One of the possible solutions will be to extend virtio bus to allow
> setting of such pre-probe parameters. However I don't know if it is
> really worth doing it,

So lets keep it as it is now.

Thanks.

>> if the device is already probed, it's too late to change the queue_num.
>>
>>
>>>> # echo virtio0 > /sys/bus/virtio/drivers/virtio_blk/bind
>>>>
>>>> # ls -l /sys/block/vda/mq/
>>>> drwxr-xr-x 10 root root 0 Sep  5 12:17 0
>>>> drwxr-xr-x 10 root root 0 Sep  5 12:17 1
>>>> drwxr-xr-x 10 root root 0 Sep  5 12:17 2
>>>> drwxr-xr-x 10 root root 0 Sep  5 12:17 3
>>>> drwxr-xr-x 10 root root 0 Sep  5 12:17 4
>>>> drwxr-xr-x 10 root root 0 Sep  5 12:17 5
>>>> drwxr-xr-x 10 root root 0 Sep  5 12:17 6
>>>> drwxr-xr-x 10 root root 0 Sep  5 12:17 7
>>>>
>>>> -Max.
>>>>
>>>>