Re: [dpdk-dev] [PATCH v6 0/4] add IOVA = VA support in KNI

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

On 12-Jul-19 10:17 AM, Jerin Jacob Kollanukkaran wrote:
> 
>> -----Original Message-----
>> From: Ferruh Yigit <ferruh.yigit@intel.com>
>> Sent: Thursday, July 11, 2019 9:52 PM
>> To: Jerin Jacob Kollanukkaran <jerinj@marvell.com>; Vamsi Krishna Attunuru
>> <vattunuru@marvell.com>; dev@dpdk.org
>> Cc: olivier.matz@6wind.com; arybchenko@solarflare.com; Burakov, Anatoly
>> <anatoly.burakov@intel.com>
>> Subject: [EXT] Re: [dpdk-dev] [PATCH v6 0/4] add IOVA = VA support in KNI
>>
>> External Email
>>
>> ----------------------------------------------------------------------
>> On 7/4/2019 10:48 AM, Jerin Jacob Kollanukkaran wrote:
>>>> From: Vamsi Krishna Attunuru
>>>> Sent: Thursday, July 4, 2019 12:13 PM
>>>> To: dev@dpdk.org
>>>> Cc: ferruh.yigit@intel.com; olivier.matz@6wind.com;
>>>> arybchenko@solarflare.com; Jerin Jacob Kollanukkaran
>>>> <jerinj@marvell.com>; Burakov, Anatoly <anatoly.burakov@intel.com>
>>>> Subject: Re: [dpdk-dev] [PATCH v6 0/4] add IOVA = VA support in KNI
>>>>
>>>> Hi All,
>>>>
>>>> Just to summarize, below items have arisen from the initial review.
>>>> 1) Can the new mempool flag be made default to all the pools and will
>> there be case that new flag functionality would fail  for some page sizes.?
>>>
>>> If the minimum huge page size is 2MB and normal huge page size is
>>> 512MB or 1G. So I think, new flags can be default as skipping the page
>> boundaries for Mempool objects has nearly zero overhead. But I leave
>> decision to maintainers.
>>>
>>>> 2) Adding HW device info(pci dev info) to KNI device structure, will it
>> break KNI on virtual devices in VA or PA mode.?
>>>
>>> Iommu_domain will be created only for PCI devices and the system runs
>>> in IOVA_VA mode. Virtual devices(IOVA_DC(don't care) or IOVA_PA
>>> devices still it works without PCI device structure)
>>>
>>> It is  a useful feature where KNI can run without root privilege and
>>> it is pending for long time. Request to review and close this
>>
>> I support the idea to remove 'kni' forcing to the IOVA=PA mode, but also not
>> sure about forcing all KNI users to update their code to allocate mempool in a
>> very specific way.
>>
>> What about giving more control to the user on this?
>>
>> Any user want to use IOVA=VA and KNI together can update application to
>> justify memory allocation of the KNI and give an explicit "kni iova_mode=1"
>> config.
> 
> Where this config comes, eal or kni sample app or KNI public API?
> 
> 
>> Who want to use existing KNI implementation can continue to use it with
>> IOVA=PA mode which is current case, or for this case user may need to force
>> the DPDK application to IOVA=PA but at least there is a workaround.
>>
>> And kni sample application should have sample for both case, although this
>> increases the testing and maintenance cost, I hope we can get support from
>> you on the iova_mode=1 usecase.
>>
>> What do you think?
> 
> IMO, If possible we can avoid extra indirection of new config. In worst case
> We can add it. How about following to not have new config
> 
> 1) Make MEMPOOL_F_NO_PAGE_BOUND  as default
> http://patches.dpdk.org/patch/55277/
> There is absolutely zero overhead of this flag considering the huge page size are minimum
> 2MB. Typically 512MB or 1GB.
> Any one has any objection?

Pretty much zero overhead in hugepage case, not so in non-hugepage case. 
It's rare, but since we support it, we have to account for it.

(also, i don't really like the name NO_PAGE_BOUND since in memzone API 
there's a "bounded memzone" allocation API, and this flag's name reads 
like objects would not be bounded by page size, not that they won't 
cross page boundary)

> 
> 2) Introduce rte_kni_mempool_create() API in kni lib to abstract the
> Mempool requirement for KNI. This will enable portable KNI applications.

This means that using KNI is not a drop-in replacement for any other 
PMD. If maintainers of KNI are OK with this then sure :)

-- 
Thanks,
Anatoly