[EXT] Re: [PATCH v1 00/10] baseband/acc200

[Maxime Coquelin]

On 9/14/22 21:57, Chautru, Nicolas wrote:
> Hi Thomas, Akhil, Bruce, Maxime,
> 
>> -----Original Message-----
>> From: Thomas Monjalon <thomas at monjalon.net>
>> Sent: Wednesday, September 14, 2022 7:23 AM
>> To: Richardson, Bruce <bruce.richardson at intel.com>; Maxime Coquelin
>> <maxime.coquelin at redhat.com>; Akhil Goyal <gakhil at marvell.com>;
>> Chautru, Nicolas <nicolas.chautru at intel.com>
>> Cc: dev at dpdk.org; hemant.agrawal at nxp.com; Vargas, Hernan
>> <hernan.vargas at intel.com>; Tom Rix <trix at redhat.com>; mdr at ashroe.eu;
>> david.marchand at redhat.com; stephen at networkplumber.org
>> Subject: Re: [EXT] Re: [PATCH v1 00/10] baseband/acc200
>>
>> 14/09/2022 15:44, Akhil Goyal:
>>>>> On 9/14/22 12:35, Thomas Monjalon wrote:
>>>>>> 06/09/2022 14:51, Tom Rix:
>>>>>>> On 9/1/22 1:34 PM, Chautru, Nicolas wrote:
>>>>>>>> From: Tom Rix <trix at redhat.com>
>>>>>>>>> On 8/31/22 6:26 PM, Chautru, Nicolas wrote:
>>>>>>>>>> From: Tom Rix <trix at redhat.com>
>>>>>>>>>>> On 8/31/22 3:37 PM, Chautru, Nicolas wrote:
> <snip>
>>>>>>>>
>>>>>>>> With regards to the pmd.h, some structure/defines are indeed
>>>>>>>> common and could be moved to a common file (for instance
>>>>>>>> turboencoder and LDPC encoder which are more vanilla and
>>>>>>>> unlikely to change for future product unlike the decoders
>>>>>>>> which have different feature set and behaviour; or some 3GPP
>>>>>>>> constant that can be defined once).  We can definitely
>>>>>>>> change these to put together shared structures/defines, but
>>>>>>>> not intending to try to artificially put things together
>>>>>>>> with spaghetti code.  We would like to keep 3 parallel
>>>>>>>> versions of these PMD for 3 different product lines which
>>>>>>>> are indeed fundamentally different designs (including
>>>>>>>> different workaround required as can be seen on the parallel
>>>>>>>> ACC100 serie under review).  - one version for FPGA
>>>>>>>> implementation (support for N3000, N6000, ...) - one version
>>>>>>>> for eASIC lookaside card implementation (ACC100, ACC101,
>>>>>>>> ...) - one version for the integrated Xeon accelerators
>>>>>>>> (ACC200, ACC300, ...)
>>>>>>>
>>>>>>> Some suggestions on refactoring,
>>>>>>>
>>>>>>> For the registers, have a common file.
>>>>>>>
>>>>>>> For the shared functionality, ex/ ldpc encoder, break these
>>>>>>> out to its own shared file.
>>>>>>>
>>>>>>> The public interface, see my earlier comments on the
>>>>>>> documentation, should be have the same interfaces and the few
>>>>>>> differences highlighted.
>>>>>>
>>>>>> +1 to have common files, and all in a single directory
>>>>>> drivers/baseband/acc100/
>>>>>
>>>>> Jus to be sure we are aligned, do you mean to have both drivers in
>>>>> the same directory, which will share some common files? That's the
>>>>> way I would go.
>>>>>
>>>>
>>>> I think the expectation is that the two drivers will diverge in
>>>> future, so having separate directories should be ok, even with
>>>> common files placed in one directory are shared with another. With
>>>> meson include paths its pretty trivial to manage if it's just header
>>>> files, and even if there are common C files, there is always the
>>>> option of using drivers/common if we want to split them out. As I
>>>> understand it, right now it's only headers inluding functions which
>>>> can be static inline, so simple sharing via include paths should work fine.
>>>>
>>> It can be ok to have 2 separate directories, but
>>> - is it not possible to have them in same directory say 'acc'  for all affiliated
>> devices.
>>> Similar to other vendors' devices (cnxk, i40e, mlx).
>>> - Can both the devices - acc100 and acc200 coexist? If not, same directory
>> is good enough.
>>> - there can be multiple files or directories in 'acc' which can be
>>> named appropriately to denote the actual device(acc100/200).
>>>
>>> Having cross dependency across different drivers of same type looks a kind
>> of hacking the meson.
>>> This was a reason we moved to have a drivers/common/ for some of the
>> drivers.
>>> Also including "../acc100/abc.h" does not look appropriate to me.
>>>
>>> IMO, we should not add unnecessary directories when the code is common
>> and can be managed in a single one.
>>>
>>> However, technically it is also ok to have 2 separate directories.
>>> But, agreeing on this will set a precedence for future next generation
>> devices from the same vendors. It may be a topic of discussion in techboard.
>>
>> Let me be frank, I don't trust Intel saying the hardware will be too much
>> different in future.
> 
> Thanks for the review and discussion.
> 
> Let me clarify, this PMD segregation is specific to ACC1xx vs ACC2xxx. There is a clear intent to have a common PMD to encompass the future multiple integrated solutions VRAN accelerators on Xeon  (based on ACC200 and future Xeon products in roadmap) but not for ACC1xx.
> Here we are splitting the  ACC1xx and the ACC2xx series (eASIC process with off-die PCIe device with on-card DDR vs a straight integrated Xeon accelerator) which are fundamentally different devices, and notably the ACC100 requiring a lot of SW workaround/mitigations/protections in the code which would not apply moving forward and would clutter the next generations which would be managed and optimized largely independently. Basically these are not just a few registers differences truly.
> Again future integrated Xeon will shared common driver but always distinct from ACC1xx (only sharing some common code and structure when possible).
> Here the refactoring effort was to gather all reusable code and structure together; which was useful indeed as there are several common functionalities and structures which could be superseded to be shared relatively seamlessly.
> 
>> For mlx5, we manage to handle very different devices (like DPU and changing
>> processors) in a single driver.
>> So I agree with Maxime and Akhil that a single driver in a single directory
>> should be enough.
>> Having different registers in different devices is not enough to split.
>>
>> The worst case would be to have a common directory acc/ but it may be a bit
>> disappointing.
>>
> 
> I believe that I hear 2 different options compatible with the 2 PMDs approach:
> - The one suggested by Akhil and Maxime I think, is to put both ACC100 and ACC200 PMDs under ./baseband/acc/ similarly to what is done for cnxk for instance. In that case the common files are still all in same directory as the 2 PMDs so we don't have do the awkard "includes += include_directories('../acc100')" in meson which was frown upon, since everything in already under /drivers/baseband/acc.
> - other option suggested by Thomas to put the shared code and structures under ./drivers/common/acc instead of being under ./drivers/acc/acc_common.h which also used for many drivers.
> 
> My preference may probably be personally for the former option at the moment, but happy to get some form of consensus on this.

I am fine with former option.
drivers/common is especially useful when code is to be shared by
different types of devices (e.g. net and crypto).

Maxime

> 
> Thanks and regards,
> Nic
>