Date: Wed, 12 Apr 2017 09:50:54 +0200 From: Vincenzo Maffione <v.maffione@gmail.com> To: Paras Jha <dreadiscool@gmail.com> Cc: FreeBSD Net <freebsd-net@freebsd.org> Subject: Re: Netmap pipe zero-copy with NIC buffer? Message-ID: <CA%2B_eA9ihEC6QmBsUskv8bmHkviNqQRekk2pS27zxrjba50XOYw@mail.gmail.com> In-Reply-To: <CAMs8r4M1wV4C5CCZcF=uTag8fd5cfBD6ovgabOt0VDKC6=9Qew@mail.gmail.com> References: <CAMs8r4O6TmHnkoMJRTKV2LZ-BejCeyvj%2BWLvc8DJAfAUWxgscQ@mail.gmail.com> <CA%2B_eA9jRKDFJnCrOyNjQFK2FXPV3E6s=D7yA0w-5k4gTBDLqqA@mail.gmail.com> <CAMs8r4M1wV4C5CCZcF=uTag8fd5cfBD6ovgabOt0VDKC6=9Qew@mail.gmail.com>
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netmap applications always bypass the kernel (network stack). There is only
a distinction between ports opened in "native" mode and "emulated" mode.
If NIC driver doesn't have native netmap support, the legacy driver is
internally used by netmap to transmit and receive (and this is called
"emulated mode").
In any case (both in native and emulated mode) the netmap application sees
netmap rings, and can zerocopy between two rings (in the same memory area)
by simply swapping the ring slots.
Of course, in emulated mode netmap internally transforms each ring slot
into and mbuf and the other way around, possibly requiring a copy. And the
whole thing is way slower.
But this is unrelated to the zerocopy thing: your application isn't aware
of the emulated or native mode and can zerocopy slots between netmap rings.
Cheers,
Vincenzo
2017-04-12 4:04 GMT+02:00 Paras Jha <dreadiscool@gmail.com>:
> Apologies, by KB I meant kernel bypass, since it is possible to open a
> netmap port without bypassing the kernel. I didn't know if this would
> affect it or not.
>
> On Sun, Apr 9, 2017 at 3:20 AM, Vincenzo Maffione <v.maffione@gmail.com>
> wrote:
>
>> Hi,
>> Yes, when you nm_open("netmap:em3{2", ...), you're opening a netmap
>> pipe in the same netmap memory area as the one used by
>> nm_open("netmap:em3", ...).
>> As a result, you can zero-copy packets from NIC rings to pipe rings.
>>
>> What do you mean by "KB mode"?
>>
>> Cheers,
>> Vincenzo
>>
>> 2017-04-08 19:56 GMT+02:00 Paras Jha <dreadiscool@gmail.com>:
>>
>>> Hi all,
>>>
>>> Is it possible to have a netmap pipe share memory with a netmap port
>>> opened
>>> in KB mode for zero-copy purposes?
>>>
>>> All the best
>>> _______________________________________________
>>> freebsd-net@freebsd.org mailing list
>>> https://lists.freebsd.org/mailman/listinfo/freebsd-net
>>> To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org"
>>>
>>
>>
>>
>> --
>> Vincenzo Maffione
>>
>
>
--
Vincenzo Maffione
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