Netmap is a framework for high-speed packet I/O from userspace. This repo is forked from the original one here. The original Netmap framework is designed for Linux 4.4 or earlier. Many of its driver's native support hasn't been updated, leaving users with only the generic emulated adapter for use. Being stuck for the same reason with my Realtek network driver, I decided to update the existing codebase for native support on Linux 6.11, which it once had for Linux 2.4 and Linux 3.2

lspci | grep net
04:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8211/8411 PCI Express Gigabit Ethernet Controller (rev 16)

This readme will also point out specific areas of code which I changed and detailed steps for installing and updating your in-tree kernel drivers. The process for out-of-tree drivers is roughly the same.

The driver code responsible for my NIC is r8169.

lsmod
Module                  Size  Used by
...			...   ...
r8169                 126976  0

Install all the required dependencies.

sudo apt-get update # update your local package index
sudo apt install build-essential # install compiling tools
sudo apt-get install -y git # install git tools
sudo apt-get install -y linux-headers-$(uname -r) # install your linux headers
sudo apt-get install linux-source # install your linux source
sudo apt-get install net-tools # install net tools for ifconfig command

After you are done with these steps, your /usr/src folder will look something like this,

cd /usr/src/
ls
linux-headers-6.11.0-13  linux-headers-6.11.0-13-generic  linux-source-6.11.0  linux-source-6.11.0.tar.bz2

If linux-source-6.11.0 is not present and you have linux-source-6.11.0.tar.bz2 instead. Then unzip it

tar -xvf linux-source-6.11.0.tar.bz2

Note: Your Linux version can differ from mine.

Although this repo contains the updates for Netmap native support on r8169 for Linux 6.11.13. The steps here are important in case you want to update your driver.

Clone the original Netmap GitHub repo in a suitable location.

git clone https://github.com/luigirizzo/netmap.git
cd netmap/LINUX

Now, the first step is to configure Netmap for your kernel and machine which is done using ./configure with relevant flags. You can try running it and observe the errors and warnings. If everything works and you don't get any warnings or errors about disabling your particular driver. Then you are good to go :)

For others, stick to this guide for solutions. The files which are of interest for r8169 are:

• configure: Contains the configuration script which creates all the Makefiles, finds your driver code, sets up everything and runs tests to adapt your environment, etc.
• final-patches/: Contains all the patch files required for modifying the native drivers with Netmap support.
• if_re_netmap_linux.h: Contains functions which act as a bridge between Netmap interface and NIC driver (in our case Realtek r8169).

First observe the latest patch for this driver available in final-patches/ viz vanilla--r8169.c--20626--30400. Since, this is a patch applied to the in-tree kernel driver find the code for this driver inside your Linux kernel. Mine happens to be here,

ls /usr/src/linux-source-6.11.0/drivers/net/ethernet/realtek/
8139cp.c  8139too.c  Kconfig  Makefile  atp.c  atp.h  r8169.h  r8169_firmware.c  r8169_firmware.h  r8169_leds.c  r8169_main.c  r8169_phy_config.c

In the earlier versions of the kernel it was a single /drivers/net/r8169.c file (Check here). But now it has been renamed and refactored into realtek folder with further classification of net into ethernet folder. Copy the realtek folder into another empty folder (say, r8169_patch) at a suitable location

mkdir r8169_patch
cd r8169_patch
cp /usr/src/linux-source-6.11.0/drivers/net/ethernet/realtek .
git init
git add .
git commit -m "initial commit"

Now, comparing with final-patches/vanilla--r8169.c--20626--30400 make the necessary changes to r8169_main.c. A nice description of what each change intends to do is presented here. After changes are done (which should be pretty quick), produce the diff file using

git diff > vanilla--realtek--60000--99999

I choose the version numbers to be 60000 which means 6.00.00 and 99999 which means 9.99.99 since, my kernel version is 6.11.13 which lies in between these versions. You can choose these accordingly as per your convenience or plans to keep generating more patches in the future.

Note: I have named the driver realtek instead of r8169.c because earlier it was just a single file, but now it is a folder and we gotta deal with the patch file for a folder as a whole.

Now, after this make the relevant changes to if_re_netmap_linux.h file, which we import near the start of our patched r8169_main.c. In my case, I just fixed 2 functions RTL_W8 and nm_kr_rxspace. If you keep this file unchanged it is fine. When you run make command it will inform you about compilation errors and you can fix them.

Now, I made relevant changes to the configure script to change the driver name from r8169.c to realtek and some other changes incorporated due to this name change as well as the change from a single file to a folder. These changes are marked with rishidarkdevil comments in the configure script. Ctrl + F all the rishidarkdevil to understand the changes made to this file. That's it!

Now run the following commands to build and install Netmap on your machine.

./configure --kernel-sources=/usr/src/linux-source-6.11.0 --no-ext-drivers --drivers=realtek --enable-vale --enable-pipe --enable-monitor --enable-ptnetmap --enable-sink
**********************************  NOTE   **********************************
*** Running some preliminary tests to customize the build environment.
*****************************************************************************
**********************************  NOTE   **********************************
*** Now running compile tests to adapt the code to your
*** kernel version. Please wait.
*****************************************************************************
kernel directory            /lib/modules/6.11.0-13-generic/build
                            [/usr/src/linux-headers-6.11.0-13-generic]
kernel sources              /usr/src/linux-source-6.11.0
linux version               60b00  [6.11]
module file                 netmap.ko

subsystems                  null sink ptnetmap generic monitor pipe vale 
apps                        dedup vale-ctl nmreplay tlem lb bridge pkt-gen 
native drivers              realtek 

Contents of the drivers.mak file:
realtek@conf := CONFIG_R8169
realtek@src := cp -Rp /usr/src/linux-source-6.11.0/drivers/net/ethernet/realtek realtek
realtek@patch := patches/vanilla--realtek--60000--99999

make
... output not shown ...

make apps

sudo make install

Unload the modules running on your NIC.

sudo rmmod r8169

Load Netmap and the patched compiled module for the NIC driver.

sudo insmod ./netmap.ko
sudo insmod ./realtek/r8169.ko

Start the interface.

sudo ifconfig enp4s0 up # and same for others

Test pkt-gen transmit using Netmap by,

sudo ethtool -K enp4s0 tx off rx off gso off tso off gro off lro off
sudo ethtool -s enp4s0 autoneg off
sudo pkt-gen -i enp4s0 -f tx -w 2 -s <SOME SOURCE IP> -d <SOME DESTINATION IP>

Here, enp4s0 is my ethernet network interface name you can get yours using ip a command.

Due to unavailability of two linux machines, I was not able to test out the receive rx performance using pkt-gen. But the above tx performance is,

• 149 Kpps on 100Mb/s line.
• ~400 Kpps on 1Gb/s line. (This is a known performance caveat related to r8169 mentioned in the original netmap page here)

This is roughly the same as the generic/emulated adapter, which seems unsurprising given that the card is not a high-speed card and the CPU can handle 1 GBps without bottlenecking, as mentioned here.

But major performance gain is seen in terms of CPU usage (measured using htop). The emulated adapter uses over 50% of a cpu core on 100Mb/s and roughly 90-100% on 1000Mb/s line, whereas the native adapter shows less than 10% cpu usage. This can be explained by the interrupts being captured by Netmap in the patched driver code rather than reaching the CPU. The following code shows the interrupts and the counter stops incrementing when pkt-gen is running with native netmap driver. In contrast, it increases at a speedy rate with the emulated driver.

watch -n1 'grep enp4s0 /proc/interrupts'

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