#Netmap userspace udp stack drivers#
#Netmap userspace udp stack driver#
#Netmap userspace udp stack full#
#Netmap userspace udp stack code#

Thus, they still think in terms of trying to move stuff in to the kernel. The problem is that most people have no experience with it. This is actually a fairly straightforward idea. Control information takes the slow path up the networking stack, the raw data takes the fast path around the stack. Most of the appliances you buy today are based on a traditional operating system like Linux, but they separate the system between the parts running the “control plane” and the parts running the “data plane”. That’s why all network appliances are based on the “control plane” vs.

#Netmap userspace udp stack drivers#

That’s why you get a 100 to 1 performance difference between custom drivers and kernel drivers. Thus, operating system kernels are designed to carry the slow rate of control information, not the fast rate of data. AT&T designed Unix to control how data was transmitted, but not to handle data transmission itself. In the digital revolution in the late 1960s and early 1970s, wires became streams of bits, and switchboards became computers. You need a switch board operator to connect your copper wire to your destination copper wire. A 100 years ago, telephones were just copper wires. The general concept we are working toward is the difference between the “control plane” and the “data plane”.

#Netmap userspace udp stack full#

It takes only 100 clock cycles to parse a UDP packet without having a full stack. There is a closed-source stack called “6windgate” which is used in a lot of appliances.īut for something like a DNS server processing UDP, or an intrusion prevention system, you don’t want a full TCP/IP stack anyway, but a degenerate stack tuned to your application. I don’t know of any open-source user-mode stack that is reliable. There are lots of these stacks around as university research projects. Your biggest problem is getting a user-mode TCP/IP stack.

#Netmap userspace udp stack driver#

You can also just grab an open-source driver and build your own. Popular choices are the PF_RING project and Intel’s DPDK, both for Linux. If you wanted to build such a DNS server, how would you do it? Well, the first step is to get one of these zero-overhead drivers. As the Intel benchmarks show, this is actually 12% the packet limit of the system. The other person said that this was impossible, because you’d hit the packets-per-second performance limit of the system. I was throwing around the number of “10 million DNS requests per second”. For example, I was having a discussion about DNS servers on Twitter. The equivalent way going through the kernel costs about 20,000 clock cycles. It doesn’t actually consume that many clock cycles, it’s just that other parts of the system start to become the limiting factor at those speeds. That works out to 200 clock cycles per packet. That means receiving the packet, processing it in user-mode (outside the kernel) and retransmission. In recent benchmark, Intel has demonstrated a system using an 8-core 2.0-GHz 1-socket server forwarding packets at a rate of 80-million packets/second. Since it does so about 1000 packets at a time in bulk, the per-packet overhead is about 50 clock cycles. The only overhead is that about once a millisecond, the CPU needs to wake up and tell the driver which packet buffers are free.

The network cards uses a feature called DMA (“direct memory access”) to copy the packet across the PCIe bus into memory, without the CPU being involved at all. The upshot is that it creates ZERO overhead networking. What memory-mapping does is that once the driver allocates physical memory, you configure the application’s page tables to point to that memory. Instead, they go through “paging tables” to get translated into physical addresses. Memory addresses in user-mode programs don’t refer to physical memory addresses. Remember that the primary difference between “kernel-mode” and “user-mode” is memory protection.

Instead, you map the packet buffers into user-mode space. Instead of a network driver that hands off packets to the kernel, you change the driver does that it doesn’t. This is done first by rewriting the network driver. Instead of moving everything into the kernel we can move everything into user-mode. For another thing, you can tap into a mid-point in the stack, so the packet doesn’t have to climb all the way to the top.īut, there is another alternative. For one thing, it gets rid of the step of copying the packet from the kernel-mode buffers to user-mode memory.

#Netmap userspace udp stack code#

That’s why “everyone knows” that you should move your code into the kernel. Every new “zero-copy” advancement has meant only removing an extra copy at one stage, but leaving copies around for other stages. It’s a funny term because there are still multiple copies involved. Over the years, Linux kernel writers have tried to optimize this with something called “zero-copy”.