Netmap TX with no impact to host

[David Belle-Isle]

Oh! Thank you soooo much! I was missing the last part about the checksum
offloadings and TSO. I disabled them and everything is working perfectly
now! Thank you so much!!

On Thu, Jan 19, 2017 at 6:00 AM, Vincenzo Maffione <v.maffione at gmail.com>
wrote:

> Hi,
>   Before answering to the question, some important disclaimers.
>
> If you are using FreeBSD-12-current, please be aware that there are IFLIB
> developments in progress that affect em devices. Unfortunately, at the
> moment netmap does not work on em/lem/igb devices because of the switch to
> IFLIB at this commit https://github.com/freebsd/freebsd/commit/
> 4bf01b136dfa554a57f25559e7a848bf32206c66. Netmap on em works correctly
> right before this commit.
>
> If you are using FreeBSD-11 versions, be aware that netmap in emulated
> mode is broken in those versions. I have the fix for that, but it is not in
> the released code. If you need it, I can give you a patch. Btw, can anyone
> point me at the procedure to push this fix to the relevant release/stable
> branches?
> If you use em devices with DEV_NETMAP enabled, emulated mode is not used,
> so it will work. If you use interfaces without DEV_NETMAP support, emulated
> netmap is used and you are affected by the broken code.
>
> Regarding your question:
> You can build a netmap program that does what you want:
> (1) transmit packets on em0 at high rates using netmap
> (2) let the host stack transmit packets on em0
> (3) let packets received on em0 to find their way to the host stack.
>
> In netmap it is possible to open just a subset of the TX rings and/or a
> subset of the RX rings.
> In your case you need to open all the TX hw rings (to acheve (1)) and the
> RX host ring (a.k.a. RX sw ring) to achieve (2).
> You achieve (3) by simply not opening the RX hw rings.
> To implement this you need two calls to nm_open() (similarly to what
> bridge does):
>
> pa = nm_open("netmap:em0/T, NULL, 0, NULL); /* open all TX hw rings */
> pb = nm_open("netmap:em0^/R, NULL, NM_OPEN_NO_MMAP, pa); /* open only RX
> host ring */
>
> Then you can use "pa" to transmit packets on the hw TX rings (1).
> To implement (2), you have two options:
>   (A) your application moves packets from the host RX ring (pb) to the hw
> TX rings (pa). In the end this is the logic of the "bridge" program does,
> so you could start from there.
>   (B) you use "transparent mode" in the host->nic direction: applications
> marks with the NS_FORWARD flag the host RX ring slots right before they
> released to the kernel, and the kernel with take care of forward them to
> the TX ring for you. However, be aware this mode is still experimental, and
> not well tested yet.
>
> Regarding the use of bridge, the correct command line for what you want to
> do (forward all packets between host stack and NIC, in both directions) is:
>
> # bridge netmap:em0
>
> However, to let TCP/UDP traffic go correctly, you need to disable tso and
> checksum offloadings on em0, since netmap will not program the NIC to
> perform those offloadings. This is also valid for your custom program above.
>
> Cheers,
>   Vincenzo
>
> 2017-01-19 2:51 GMT+01:00 David Belle-Isle <dbelleisle at gmail.com>:
>
>> Hi,
>>
>> I'm trying to open a netmap descriptor to an interface to send packets.
>> However, I don't want to prevent the host to send and receive data
>> (transparent). I don't think this should be hard but I can't figure out
>> how
>> to do this.
>>
>> I tried to run the bridge example in the FreeBSD distribution but even
>> that
>> I can't get to run without stopping the host's networking completely. I
>> tried running ./bridge em0 em0 which, if I understand correctly should
>> open
>> the NIC and host rings and pass the traffic through. As soon as I start it
>> all the networking stops.
>>
>> I tried testing in a VMware VM and on bare-metal with em cards and got the
>> same results with both.
>>
>> Can someone help me?
>>
>> Thanks,
>>
>> David
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>
>
>
> --
> Vincenzo Maffione
>