Re: [dpdk-dev] DPDK and HW offloads

["Qiu, Michael" <michael.qiu@intel.com>]

On 3/22/2016 6:20 PM, Richardson, Bruce wrote:
> On Tue, Mar 22, 2016 at 05:50:28AM +0000, Qiu, Michael wrote:
>> On 3/21/2016 11:27 PM, Kyle Larose wrote:
>>> On Mon, Mar 21, 2016 at 10:52 AM, Bruce Richardson
>>> <bruce.richardson@intel.com> wrote:
>>>> On Sun, Mar 20, 2016 at 08:18:57PM +0100, Thomas Monjalon wrote:
>>>>> 2016-03-20 14:17, Zhang, Helin:
>>>>>> From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
>>>>>>> 2016-03-18 10:16, Stephen Hemminger:
>>>>>>>> Right now, all those offload features are pretty much unusable in a
>>>>>>>> real product without lots and lots of extra codes and huge bug
>>>>>>>> surface. It bothers me enough that I would recommend removing much of the
>>>>>>> filter/offload/ptype stuff from DPDK!
>>>>>>>
>>>>>>> One of the biggest challenge is to think about a good filtering API.
>>>>>>> The offloading has some interaction with the mbuf struct.
>>>>>>>
>>>>>>> I would like to suggest rewriting ethdev API by keeping it as is for some time for
>>>>>>> compatibility while creating a new one. What about the prefix dpdk_netdev_ to
>>>>>>> progressively replace rte_eth_dev?
>>>>>> I totally agree with to add new and generic APIs for user applications. But I don't
>>>>>> think we need to remove all current APIs. Generic APIs may not support all advanced
>>>>>> hardware features, while specific APIs can. Why not support all? One generic APIs for
>>>>>> common users, and others APIs for advanced users.
>>>>> Yes we cannot access to every features of a device through generic API.
>>>>> Until now we were trying to add an ethdev API for every features even if it
>>>>> is used by only one driver.
>>>>> I think we should allow a direct access to the driver by the applications and
>>>>> work on generic API only for common features.
>>>> Definite +1.
>>>> I think that we need to start pushing driver-specific functionality to get exposed
>>>> via a driver's header files. That allow users who want to extract the max
>>>> functionality from a particular NIC to do so via those APIs calls, while not
>>>> polluting the generic ethdev layer.
>>>>
>>> What sort of requirements on ABI/API compatibility would this place on
>>> the drivers? I would hope that it would be treated like any other
>>> public API within DPDK. I don't think this would be too onerous, but
>>> it would require that the drivers be designed to deal with it. (I.e.
>>> don't just expose any old internal driver function).
>> Why not to implement one simple API with variable arguments, just like
>> syscall ioctl() does. And drivers implement it's specific hardware
>> features with a feature bit param, and other needed variable arguments.
>>
>> Thanks,
>> Michael
> A very much dislike that idea. 
> * It makes the code much harder to read as you have to closely examine all the
>   parameters to work out what a function call is actually meant to do.

It's not a big deal, if we have a document.

> * It makes it much harder to see that you have an implicit dependency on a
>   specific device. Having to include a driver specific header file e.g. i40e.h,
>   and call a function named e.g. i40e_do_magic_stuff(), makes it pretty explicit
>   that you have a dependency on i40e-based hardware

Software does not want to bind to specific hardware I think, what about
the transportability?

> * It prevents the compiler from doing type-checking on parameters and informing
>   you of little inconsistencies.

Maybe, we could do self-check for the parameters I think.

>
> For all these reasons, I prefer the device-specific functions option. However,
> at the same time, we also need to ensure we have a reasonable set of generic
> APIs so that the cases where users are forced to drop down to the lower-level
> device-specific primitives are reduced.

For software, it do not care which hardware it is, it only cares about
what ability you have.

Thanks,
Michael

> Regards,
> /Bruce
>
>>>> On the other hand, I don't like the idea of dpdk_netdev. I think we can work
>>>> within the existing rte_eth_dev framework.
>>>>
>>>> /Bruce
>>>>
>>