Re: [dpdk-dev] [PATCH 0/6] introduce DMA memory mapping for external memory

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 17-Feb-19 6:18 AM, Shahaf Shuler wrote:
> Thursday, February 14, 2019 6:20 PM, Burakov, Anatoly:
>> Subject: Re: [dpdk-dev] [PATCH 0/6] introduce DMA memory mapping for
>> external memory
>>
>> On 14-Feb-19 1:28 PM, Shahaf Shuler wrote:
>>> Thursday, February 14, 2019 12:19 PM, Burakov, Anatoly:
>>>> Subject: Re: [dpdk-dev] [PATCH 0/6] introduce DMA memory mapping for
>>>> external memory
>>>>
>>>> On 13-Feb-19 7:24 PM, Shahaf Shuler wrote:
>>>>> Wednesday, February 13, 2019 1:43 PM, Alejandro Lucero:
>>>>>> Subject: Re: [dpdk-dev] [PATCH 0/6] introduce DMA memory mapping
>>>>>> for external memory
>>>>>>
> 
> [...]
> 
>>>
>>> If we are going to force all to use the extmem, then there is no need w/
>> this API. we can have the PMDs to register when the memory is registered.
>>> We can just drop the vfio_dma_map APIs and that's it.
>>>
>>
>> Well, whether we needed it or not is not really my call, but what i can say is
>> that using extmem_register is _necessary_ if you're going to use the PMD's.
>> You're right, we could just map memory for DMA at register time - that
>> would save one API call to get the memory working. It makes it a bit weird
>> semantically, but i think we can live with that :)
> 
> This was not my suggestion 😊. I don't think the register API should do the mapping as well.
> My thoughts were on one of the two options:
> 1. have the series I propose here, and enable the user to work with memory managed outside of DPDK. Either force the user to call rte_extmem_register before the mapping or devices which needs memory to be also registered in the DPDK system can fail the mapping.
> 2. not providing such option to application, and forcing applications to populate a socket w/ external memory.
> 
> I vote for #1.

I too think #1 is better - we want this to be a valid use case. Allowing 
such usage in the first place is already gracious enough - all we ask in 
return is one extra API call, to politely let DPDK know that this memory 
exists and is going to be used for DMA :)

Also, having the memory registered will also allow us to refuse mapping 
if it cannot be found in DPDK maps - if rte_virt2memseg returns NULL, 
that means extmem_register was not called. I.e. we can _enforce_ usage 
of extmem_register, which i believe is a good thing for usability.

> 
>>
>> --
>> Thanks,
>> Anatoly


-- 
Thanks,
Anatoly