Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Max Gurtovoy <mgurtovoy@nvidia.com>]

On 9/6/2021 2:20 PM, Michael S. Tsirkin wrote:
> On Mon, Sep 06, 2021 at 01:31:32AM +0300, Max Gurtovoy wrote:
>> On 9/5/2021 7:02 PM, Michael S. Tsirkin wrote:
>>> On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
>>>> On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
>>>>> Sometimes a user would like to control the amount of IO queues to be
>>>>> created for a block device. For example, for limiting the memory
>>>>> footprint of virtio-blk devices.
>>>>>
>>>>> Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
>>>>> ---
>>>>>
>>>>> 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 | 20 +++++++++++++++++++-
>>>>>    1 file changed, 19 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
>>>>> index 4b49df2dfd23..9332fc4e9b31 100644
>>>>> --- a/drivers/block/virtio_blk.c
>>>>> +++ b/drivers/block/virtio_blk.c
>>>>> @@ -24,6 +24,22 @@
>>>>>    /* 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);
>>>>> +}
>
> Hmm which tree is this for?

I've mentioned in the note that it apply on branch for-5.15/drivers. But 
now you can apply it on linus/master as well.


>
>>>>> +
>>>>> +static const struct kernel_param_ops queue_count_ops = {
>>>>> +	.set = virtblk_queue_count_set,
>>>>> +	.get = param_get_uint,
>>>>> +};
>>>>> +
>>>>> +static unsigned int num_io_queues;
>>>>> +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
>>>>> +MODULE_PARM_DESC(num_io_queues,
>>>>> +		 "Number of IO virt queues to use for blk device. Should > 0");
>
>
> better:
>
> +MODULE_PARM_DESC(num_io_request_queues,
> +                "Limit number of IO request virt queues to use for each device. 0 for now limit");

You proposed it and I replied on it bellow.


>
>
>>>>> +
>>>>>    static int major;
>>>>>    static DEFINE_IDA(vd_index_ida);
>>>>> @@ -501,7 +517,9 @@ 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_io_queues, nr_cpu_ids),
>>>>> +			num_vqs);
>>>> If you respin, please consider calling them request queues. That's the
>>>> terminology from the VIRTIO spec and it's nice to keep it consistent.
>>>> But the purpose of num_io_queues is clear, so:
>>>>
>>>> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
>>> I did this:
>>> +static unsigned int num_io_request_queues;
>>> +module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
>>> +MODULE_PARM_DESC(num_io_request_queues,
>>> +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
>> The parameter is writable and can be changed and then new devices might be
>> probed with new value.
>>
>> It can't be zero in the code. we can change param_set_uint_minmax args and
>> say that 0 says nr_cpus.
>>
>> I'm ok with the renaming but I prefer to stick to the description we gave in
>> V3 of this patch (and maybe enable value of 0 as mentioned above).