[dpdk-dev] Reg DPDK & PMD

[dpdk-dev] Reg DPDK & PMD

[raman geetha gopalakrishnan]

Hi All,

I have the following basic question. Hope to get an answer / link where i
can get myself clear.

1. In DPDK PMD is optimized driver for an given NIC to get maximum
performance.
    That being the case why we are talking about DPDK supported NICs.

     A) My assumption is that NIC interface is standardized so that PMD
should actually work with any NIC (barring some NIC specific performance
tweaks)
          is that correct?

     B) if #A is correct , how can i make changes to PMD to support any NIC
?

if i have to put the above question in different way then it is

2. what is preventing us from having a common PMD layer for all NICs and
additional PMD specific to each NIC???

Thanks
Raman

Re: [dpdk-dev] Reg DPDK & PMD

[Bruce Richardson]

On Wed, Mar 08, 2017 at 07:05:03PM +0530, raman geetha gopalakrishnan wrote:
> Hi All,
> 
> I have the following basic question. Hope to get an answer / link where i
> can get myself clear.
> 
> 1. In DPDK PMD is optimized driver for an given NIC to get maximum
> performance.
>     That being the case why we are talking about DPDK supported NICs.
> 
>      A) My assumption is that NIC interface is standardized so that PMD
> should actually work with any NIC (barring some NIC specific performance
> tweaks)
>           is that correct?

No, that assumption is not correct, which is the reason we have so many
NIC drivers in DPDK. Each NIC uses a different method of talking to SW,
both in terms of the registers needed to be accessed to initialize the
NIC and then in terms of the metadata format used to receive or transmit
packets.

Regards,
/Bruce

> 
>      B) if #A is correct , how can i make changes to PMD to support any NIC
> ?
> 
> if i have to put the above question in different way then it is
> 
> 2. what is preventing us from having a common PMD layer for all NICs and
> additional PMD specific to each NIC???
> 
> Thanks
> Raman

Re: [dpdk-dev] Reg DPDK & PMD

[Ferruh Yigit]

On 3/8/2017 1:35 PM, raman geetha gopalakrishnan wrote:
> Hi All,
> 
> I have the following basic question. Hope to get an answer / link where i
> can get myself clear.
> 
> 1. In DPDK PMD is optimized driver for an given NIC to get maximum
> performance.
>     That being the case why we are talking about DPDK supported NICs.
> 
>      A) My assumption is that NIC interface is standardized so that PMD
> should actually work with any NIC (barring some NIC specific performance
> tweaks)
>           is that correct?

PMDs (Poll Mode Drivers) are _real_ device drivers, they are not an
optimization layer on top off a standardized interface, they deal
directly with hardware, so needs to be specific to hardware.

> 
>      B) if #A is correct , how can i make changes to PMD to support any NIC
> ?
> 
> if i have to put the above question in different way then it is
> 
> 2. what is preventing us from having a common PMD layer for all NICs and
> additional PMD specific to each NIC???
> 
> Thanks
> Raman
> 

Re: [dpdk-dev] Reg DPDK & PMD

[Wiles, Keith]

> On Mar 8, 2017, at 8:25 AM, Ferruh Yigit <ferruh.yigit@intel.com> wrote:
> 
> On 3/8/2017 1:35 PM, raman geetha gopalakrishnan wrote:
>> Hi All,
>> 
>> I have the following basic question. Hope to get an answer / link where i
>> can get myself clear.
>> 
>> 1. In DPDK PMD is optimized driver for an given NIC to get maximum
>> performance.
>>    That being the case why we are talking about DPDK supported NICs.
>> 
>>     A) My assumption is that NIC interface is standardized so that PMD
>> should actually work with any NIC (barring some NIC specific performance
>> tweaks)
>>          is that correct?
> 
> PMDs (Poll Mode Drivers) are _real_ device drivers, they are not an
> optimization layer on top off a standardized interface, they deal
> directly with hardware, so needs to be specific to hardware.
> 
>> 
>>     B) if #A is correct , how can i make changes to PMD to support any NIC
>> ?
>> 
>> if i have to put the above question in different way then it is
>> 
>> 2. what is preventing us from having a common PMD layer for all NICs and
>> additional PMD specific to each NIC???

Another minor point is DPDK has a generic API layer for the ethernet NICs it is called ethdev with a set of standard APIs for the application. The PMDs attached themselves to the ethdev using standardized APIs, which is about as close we can get to a standard interface to PMDs/hardware.

>> 
>> Thanks
>> Raman
>> 
> 

Regards,
Keith

Re: [dpdk-dev] Reg DPDK & PMD

[raman geetha gopalakrishnan]

Thanks  a lot Bruce to correct my assumption. This was what i looked for.

Thanks
Raman

On Wed, Mar 8, 2017 at 7:46 PM, Bruce Richardson <bruce.richardson@intel.com
> wrote:

> On Wed, Mar 08, 2017 at 07:05:03PM +0530, raman geetha gopalakrishnan
> wrote:
> > Hi All,
> >
> > I have the following basic question. Hope to get an answer / link where i
> > can get myself clear.
> >
> > 1. In DPDK PMD is optimized driver for an given NIC to get maximum
> > performance.
> >     That being the case why we are talking about DPDK supported NICs.
> >
> >      A) My assumption is that NIC interface is standardized so that PMD
> > should actually work with any NIC (barring some NIC specific performance
> > tweaks)
> >           is that correct?
>
> No, that assumption is not correct, which is the reason we have so many
> NIC drivers in DPDK. Each NIC uses a different method of talking to SW,
> both in terms of the registers needed to be accessed to initialize the
> NIC and then in terms of the metadata format used to receive or transmit
> packets.
>
> Regards,
> /Bruce
>
> >
> >      B) if #A is correct , how can i make changes to PMD to support any
> NIC
> > ?
> >
> > if i have to put the above question in different way then it is
> >
> > 2. what is preventing us from having a common PMD layer for all NICs and
> > additional PMD specific to each NIC???
> >
> > Thanks
> > Raman
>