Re: [dpdk-dev] [EXT] Re: [PATCH v11 2/4] eal: add legacy kni option

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 10/21/2019 2:13 PM, Vamsi Krishna Attunuru wrote:
> 
> 
>> -----Original Message-----
>> From: Ferruh Yigit <ferruh.yigit@intel.com>
>> Sent: Monday, October 21, 2019 5:25 PM
>> To: Vamsi Krishna Attunuru <vattunuru@marvell.com>; dev@dpdk.org
>> Cc: thomas@monjalon.net; Jerin Jacob Kollanukkaran <jerinj@marvell.com>;
>> Kiran Kumar Kokkilagadda <kirankumark@marvell.com>;
>> olivier.matz@6wind.com; anatoly.burakov@intel.com;
>> arybchenko@solarflare.com; stephen@networkplumber.org
>> Subject: [EXT] Re: [dpdk-dev] [PATCH v11 2/4] eal: add legacy kni option
>>
>> External Email
>>
>> ----------------------------------------------------------------------
>> On 10/21/2019 9:03 AM, vattunuru@marvell.com wrote:
>>> From: Vamsi Attunuru <vattunuru@marvell.com>
>>>
>>> This adds a "--legacy-kni" command-line option. It will be used to run
>>> existing KNI applications with DPDK 19.11 and later.
>>>
>>> Signed-off-by: Vamsi Attunuru <vattunuru@marvell.com>
>>> Suggested-by: Ferruh Yigit <ferruh.yigit@intel.com>
>>
>> <...>
>>
>>> diff --git a/lib/librte_eal/common/eal_options.h
>>> b/lib/librte_eal/common/eal_options.h
>>> index 9855429..1010ed3 100644
>>> --- a/lib/librte_eal/common/eal_options.h
>>> +++ b/lib/librte_eal/common/eal_options.h
>>> @@ -69,6 +69,8 @@ enum {
>>>  	OPT_IOVA_MODE_NUM,
>>>  #define OPT_MATCH_ALLOCATIONS  "match-allocations"
>>>  	OPT_MATCH_ALLOCATIONS_NUM,
>>> +#define OPT_LEGACY_KNI      "legacy-kni"
>>> +	OPT_LEGACY_KNI_NUM,
>>>  	OPT_LONG_MAX_NUM
>>>  };
>>
>> Two concerns,
>>
>> 1- "legacy-kni" doesn't have enough context
>>
>> 2- I prefer to keep existing behavior default, at least for a while, something
>> like next LTS etc, meanwhile this patch can be around for a good time and
>> can be good to switch.
>>
>> Based on above to, what do you think to rename the option to 'kni-iova-va',
>> if not set by default it will be "IOVA=PA", when set it will enable "IOVA=VA"
>> mode?
> 
> Hi Ferruh,
> 
> I think the new eal flag(legacy-kni) is quite intuitive. Since release notes will be having the required details about it's purpose and how it enables users to use existing applications on latest dpdk.

what exactly 'legacy' means, what has been changed, is the old one completely
replaced/re-written ????, but whoever not following what is happening won't
underase tand what is old in the KNI, digging through release notes and commits
will give this information but it will be hard to get it from binary and get
harder by a few releases passed.

> 
> Current EAL does set iova as va if bus iommu returns DC, meaning iova=va is the kind of default mode(in most of use cases) and for running kni, we have to explicitly set the flag to run kni in iova=va mode all the time. I think having a flag for legacy usage(PA mode) is more appropriate than having kni-iova-va kind of flag.

It is about keeping the existing behavior same, right now if the kni module is
inserted it will force the PA mode. With your update it will be possible to run
iova=va with kni module inserted when flag is set. I suggest giving some time to
this new behavior before making it default.

> 
> Otx2 net pmd that runs on Octeontx2 platforms only supports iova=va mode, we would like to have KNI running by default without any flags passed.   
> 

I see, but other way around will affect all existing KNI users, they will either
need to add this flag or update their application.

This is new feature, who want to use it adding a specific flag makes more sense
to me than all old users have to add the flag.