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

[Max Gurtovoy <mgurtovoy@nvidia.com>]

On 10/24/2021 10:19 AM, Max Gurtovoy wrote:
>
> On 10/22/2021 12:30 PM, Michael S. Tsirkin wrote:
>> On Thu, Sep 02, 2021 at 11:46:22PM +0300, Max Gurtovoy wrote:
>>> Sometimes a user would like to control the amount of request queues to
>>> be created for a block device. For example, for limiting the memory
>>> footprint of virtio-blk devices.
>>>
>>> Reviewed-by: Christoph Hellwig <hch@lst.de>
>>> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
>>> Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
>>> ---
>>>
>>> changes from v2:
>>>   - renamed num_io_queues to num_request_queues (from Stefan)
>>>   - added Reviewed-by signatures (from Stefan and Christoph)
>>>
>>> changes from v1:
>>>   - use param_set_uint_minmax (from Christoph)
>>>   - added "Should > 0" to module description
>>>
>>> Note: This commit apply on top of Jens's branch for-5.15/drivers
>>>
>>> ---
>>>   drivers/block/virtio_blk.c | 21 ++++++++++++++++++++-
>>>   1 file changed, 20 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
>>> index 4b49df2dfd23..aaa2833a4734 100644
>>> --- a/drivers/block/virtio_blk.c
>>> +++ b/drivers/block/virtio_blk.c
>>> @@ -24,6 +24,23 @@
>>>   /* The maximum number of sg elements that fit into a virtqueue */
>>>   #define VIRTIO_BLK_MAX_SG_ELEMS 32768
>>>   +static int virtblk_queue_count_set(const char *val,
>>> +        const struct kernel_param *kp)
>>> +{
>>> +    return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
>>> +}
>>> +

BTW, I've noticed in your new message you allow setting 0 so you might 
want to change the code to

param_set_uint_minmax(val, kp, 0, nr_cpu_ids);

to a case a user will load the module with num_request_queues=0.

>>> +static const struct kernel_param_ops queue_count_ops = {
>>> +    .set = virtblk_queue_count_set,
>>> +    .get = param_get_uint,
>>> +};
>>> +
>>> +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");
>>> +
>>>   static int major;
>>>   static DEFINE_IDA(vd_index_ida);
>> I wasn't happy with the message here so I tweaked it.
>>
>> Please look at it in linux-next and confirm. Thanks!
>
> Looks good.
>
>
>>
>>
>>> @@ -501,7 +518,9 @@ static int init_vq(struct virtio_blk *vblk)
>>>       if (err)
>>>           num_vqs = 1;
>>>   -    num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
>>> +    num_vqs = min_t(unsigned int,
>>> +            min_not_zero(num_request_queues, nr_cpu_ids),
>>> +            num_vqs);
>>>         vblk->vqs = kmalloc_array(num_vqs, sizeof(*vblk->vqs), 
>>> GFP_KERNEL);
>>>       if (!vblk->vqs)
>>> -- 
>>> 2.18.1