[dpdk-dev] [RFC] ethdev: use special speed for virtual Ethernetdevices

[Ivan Dyukov]

01.04.2020 13:06, Morten Brørup пишет:
>> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Thomas Monjalon
>> Sent: Wednesday, April 1, 2020 11:54 AM
>>
>> 01/04/2020 11:33, Morten Brørup:
>>> Thomas, Ferruh, Andrew (Ethernet API Maintainers),
>>>
>>> A command line option was recently added to set which speed a vNIC
>> reports when the link is up. This makes sense for Spanning Tree and
>> other protocols which depend on link speed.
>>
>> Please could you reference the patch?
> It is a patch for the virtio driver:
> https://protect2.fireeye.com/url?k=e37beb37-beabe3df-e37a6078-000babff32e3-4aaaa0986ed7ec57&u=http://inbox.dpdk.org/dev/20191212085012.9170-1-i.dyukov@samsung.com/T/#m052f90ea8c559406aeaefaea1fc24ed9bb573788
This patch is related to similar work in qemu & kernel virtio driver. 
Please see 
https://lists.oasis-open.org/archives/virtio-comment/201911/msg00058.html. 
These changes have been implemented and released in kernel and qemu. 
speed is negotiated from qemu and then user may change the speed of 
virtio device using ethtool utility. I have added similiar patchset for 
pmd driver which do the same but for changing speed I used devargs 
instead of ethtool.
>
>>> However, I suspect that this workaround rarely reflects the physical
>> truth, and suggest that the application should handle it instead.
>>
>> I don't understand why we need to define some speed for virtual
>> devices.
>>
>>> In other words... Instead of faking it in the virtual Ethernet
>> drivers, I suggest that rte_ethdev.h defines a special speed value for
>> vNICs which really don't have a physical link speed:
>>> #define ETH_SPEED_NUM_NONE         0 /**< Not defined */
>> The only issue with this constant is the lack of RTE_ prefix :-)
>> Otherwise I think "0 - NONE - not defined" fits well with virtual
>> device case.
>>
>>> +#define ETH_SPEED_NUM_UNKNOWN      1 /**< Unknown (virtual device)
>> */
>>
>> 1 means 1 Mbps
>>
>>> #define ETH_SPEED_NUM_10M         10 /**<  10 Mbps */
>>>
>>> Alternatively, we could expand the meaning of ETH_SPEED_NUM_NONE:
>>>
>>> -#define ETH_SPEED_NUM_NONE         0 /**< Not defined */
>>> +#define ETH_SPEED_NUM_NONE         0 /**< Not defined or unknown
>> (virtual device) */
>>
>> Yes I agree with extending the comment for NONE.
>>
>>> The special value could also be used in cases like this:
>>>
>> https://protect2.fireeye.com/url?k=6154668d-3c846e65-6155edc2-000babff32e3-bf63d034253cac80&u=http://inbox.dpdk.org/dev/AM0PR0502MB401907ADE7CEA27DC642DF35D2CB0@AM0P
>> R0502MB4019.eurprd05.prod.outlook.com/T/#t
>>
>> Yes, if speed is unknown, it should be reported as 0.
> So the next related question is: Should a vNIC be allowed to report a fake speed if it does not know that the underlying hardware actually provides this speed?
>