Advantages of Netmap NM_OPEN_NO_MMAP

[Paras Jha]

Hi,

Thanks for the quick reply, it clarified things for me. Regarding the idea
of independent TX-RX ring couples per thread, would a possible variation of
this methodology be 1 RX ring per interface (only one thread reads), but *x*
amount of TX rings, where *x *is the number of threads. Am I correct in
assuming that such a structure will allow lockless zero-copy between an
arbitrary number of interfaces (3 or greater)?

Regards

On Thu, Nov 17, 2016 at 5:11 PM, Vincenzo Maffione <v.maffione at gmail.com>
wrote:

> Hi,
>   No, each interface open in netmap mode has its own netmap buffers (for
> packet data) and netmap rings, independently of what is the netmap memory
> region where buffers/rings resides.
> Two applications using different interfaces can work independently on each
> other (no locks needed), it does not matter whether they are in the same
> netmap memory region or not, because the data structures (rings and
> buffers) are separated.
> It does matter in terms of isolation, of course: two applications using
> the same shared memory must trust each other.
>
> Typically you want two interfaces to be in the same netmap memory region
> because you want an application to do zerocopy packet forwarding between
> the two interfaces.
> Also in this case locks are not usually needed, since you would have a
> single thread accessing both interfaces. (Or you could have a separate
> thread for each TX-RX ring couple, but always without using locks.)
>
> You can imagine a netmap memory region as a pool of buffers and rings,
> where one or more interfaces can allocate their buffers/rings when they
> enter netmap mode (deallocation is on exit from netmap mode).
> Your system can have many memory regions. By default all the physical
> interfaces share the same memory region, while each VALE port uses a
> private memory region.
> This is however being changed to ease arbitrary association between
> interfaces and memory regions.
>
> Cheers,
>   Vincenzo
>
> 2016-11-17 22:50 GMT+01:00 Paras Jha <dreadiscool at gmail.com>:
>
>> Hi all,
>>
>> I had a quick question about some of the implications of sharing packet
>> buffer memory between multiple interfaces. Assuming an arbitrary amount of
>> interfaces (> 2) are linked together with NM_OPEN_NO_MMAP and share the
>> same memory, would this have any issues with lock contention?
>>
>> Sorry in advance if this is the wrong place to post, I had seen several
>> other archives about Netmap on this mailing list and I thought it was the
>> most appropriate place.
>>
>> Regards
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>
>
>
> --
> Vincenzo Maffione
>