rvs: a virtual switch, aiming to be rapid and platform-independent

rvs is a rapid virtual switch that aims to be platform-independent so that it can be integrated into a wide range of systems.

rvs forwards packets from a virtual interface, called rvif, to other rvif(s); each rvif is instantiated over a shared memory file, and can be associated with a process/system through the file interface.

The forwarding plane of rvs is inspired by VALE/mSwitch that is a netmap-based virtual switch.

The primary motivation of rvs is to have the simplest implementation of a high-performance virtual switch, which does not depend on external libraries; netmap is highly flexible and sophisticated, however, it is sometimes too much for small tests and requires a bit of engineering to port specific components (e.g., the packet switching logic of VALE) to other environments (e.g., running the VALE switch in user-space, rather than in the kernel).

A DPDK poll mode driver (pmd) for rvif is found at https://github.com/yasukata/librte_pmd_rvif.

How to use

This repository contains two example applications: an rvs packet forwarder (apps/fwd) and a packet generator (apps/pkt-gen).

Compilation

Please enter the top directory of this repository.

cd rvs

The following compiles the fwd application.

make -C apps/fwd

The following compiles the pkt-gen application.

make -C apps/pkt-gen

Example

Let's forward packets between two pkt-gen processes through the fwd application; we try the topology illustrated below.

[pkt-gen app tx] --> [fwd app] --> [pkt-gen app rx]

First, please create two of 32 MB shared memory files by the following commands; in this example, /dev/shm/rvs_shm00 is used as the rvif for the sender, and /dev/shm/rvs_shm01 is used for the rvif of the receiver.

dd if=/dev/zero of=/dev/shm/rvs_shm00 bs=1M count=0 seek=32

dd if=/dev/zero of=/dev/shm/rvs_shm01 bs=1M count=0 seek=32

Please open a terminal/console and type the following command to run the fwd application; the following executes the rvs logic and forwards packets between rvifs made on /dev/shm/rvs_shm00 and /dev/shm/rvs_shm01.

./apps/fwd/a.out -m /dev/shm/rvs_shm00 -m /dev/shm/rvs_shm01

Then, please open another terminal/console and type the following command to launch the receiver pkt-gen process.

./apps/pkt-gen/a.out -m /dev/shm/rvs_shm01 -S 01:23:35:67:89:ab -D ff:ff:ff:ff:ff:ff -s 192.168.123.3 -d 255.255.255.255 -f rx

At last, please open another terminal/console and type the following command to launch the sender pkt-gen process.

./apps/pkt-gen/a.out -m /dev/shm/rvs_shm00 -S 01:23:35:67:89:aa -D 01:23:35:67:89:ab -s 192.168.123.2 -d 192.168.123.3 -f tx -l 64

The following is the example output.

fwd

$ ./apps/fwd/a.out -m /dev/shm/rvs_shm00 -m /dev/shm/rvs_shm01
port[0]: /dev/shm/rvs_shm00 (0x7fe5749a4000)
port[1]: /dev/shm/rvs_shm01 (0x7fe5729a4000)
-- FWD --
   0.000001 Mpps
   0.955904 Mpps
  13.261311 Mpps
  13.245440 Mpps
  13.252096 Mpps
  13.236734 Mpps

pkt-gen rx

$ ./apps/pkt-gen/a.out -m /dev/shm/rvs_shm01 -S 01:23:35:67:89:ab -D ff:ff:ff:ff:ff:ff -s 192.168.123.3 -d 255.255.255.255 -f rx
/dev/shm/rvs_shm01 is mapped at 0x7f85e455e000 (33554432 bytes)
rvif uses 10543104 bytes
src 01:23:35:67:89:ab (192.168.123.3) dst ff:ff:ff:ff:ff:ff (255.255.255.255)
-- RX --
    0.000 Mpps (    0.000 Gbps )
    8.936 Mpps (    4.575 Gbps )
   13.275 Mpps (    6.796 Gbps )
   13.262 Mpps (    6.790 Gbps )
   13.261 Mpps (    6.790 Gbps )

pkt-gen tx

$ ./apps/pkt-gen/a.out -m /dev/shm/rvs_shm00 -S 01:23:35:67:89:aa -D 01:23:35:67:89:ab -s 192.168.123.2 -d 192.168.123.3 -f tx -l 64
/dev/shm/rvs_shm00 is mapped at 0x7f9fe5902000 (33554432 bytes)
rvif uses 10543104 bytes
src 01:23:35:67:89:aa (192.168.123.2) dst 01:23:35:67:89:ab (192.168.123.3)
-- TX --
   13.245 Mpps (    6.781 Gbps )
   13.243 Mpps (    6.780 Gbps )
   13.252 Mpps (    6.785 Gbps )
   13.243 Mpps (    6.780 Gbps )

Here, we observe 13 Mpps (million packets per second) for 64-byte packets.

Command options of the example applications

apps/fwd

-m: specifies a shared memory file of an rvif attached to an rvs instance
-b: batch size to forward packtes

apps/pkt-gen

-d: destination IP address set in the TX packets
-D: destination MAC address set in the TX packets
-f: specifies the role either rx or tx
-l: size of the TX packets (in byte)
-m: specifies a shared memory file used as an rvif
-s: source IP address set in the TX packets
-S: source MAC address set in the TX packets
-t: number of threads

NOTE: the rx mode of apps/pkt-gen transmits a single packet during the initialization phase so that the learning bridge logic in rvs can learn the pair of the port and the rvif MAC address.

Internals

Packet forwarding logic

The packet forwarding logic presented in Section 3.3.1 of the VALE paper is equivalent to the following parts.

Marked by // stage 2, compute destinations in the figure of the paper. https://github.com/yasukata/rvs/blob/6ec2d454ca0e0b405503897c1e711bd9dbc64dd9/rvs.c#L40-L65

Marked by // stage 3, forward, looping on ports in the figure of the paper. https://github.com/yasukata/rvs/blob/6ec2d454ca0e0b405503897c1e711bd9dbc64dd9/rvs.c#L67-L98

The paper has the code block // stage 1, build batches and prefetch, but this part is a bit different in rvs; in rvs, the batch size is controlled through the batch argument passed to unsigned short rvs_fwd(struct rvs *vs, unsigned short vid, unsigned short qid, unsigned short batch).

To customize the packet forwarding logic, we should modify the following code block, which looks up the destination of a packet. https://github.com/yasukata/rvs/blob/6ec2d454ca0e0b405503897c1e711bd9dbc64dd9/rvs.c#L46-L61

rvif interface

The definition of struct rvif is as follows. https://github.com/yasukata/rvs/blob/6ec2d454ca0e0b405503897c1e711bd9dbc64dd9/include/rvif.h#L22-L42

rvs assumes the top of struct rvif is located at the top of a shared memory file.

This rvif representation aims to allow a process/system to configure the queues of its rvif; the process/system can configure the number of queues and the number of slots/descriptors for an rvif.

rvif.num represents the number of queues.

Each queue has two rings, and ring[0] is for RX and ring[1] is for TX.

rvif.queue[queue_id].ring[0].num represents the number of RX slots/descriptors of the rvif.queue[queue_id].

rvif.queue[queue_id].ring[1].num represents the number of TX slots/descriptors of the rvif.queue[queue_id].

Each ring has the head/tail indexes, which indicate the slots/descriptors to be consumed; if head and tail are the same, it means nothing to be consumed.

The process/system, that performs I/O over the rvif, updates tail, and rvs updates head.

Each slot has two fields off and len.

off is used for pointing a packet buffer at the address (unsnigned long) vif + slot[slot_id].off.

rvs assumes the size of a packet buffer associated with a slot is always 2048 bytes, that is aligned by 2048 bytes.

len is used for the TX path, and indicates the packet size.

Portability of rvs

rvs aims to be as portable as possible.

While it is not mandatory, we specify -std=c89 -nostdlib -nostdinc for the CFLAGS in the Makefile of the fwd application to ensure the rvs implementation does not require external libraries.

Lock implementations are usually platform-dependent because they typically use atomic CPU operations; therefore, the rvs implementation assumes the lock implementation is provided by the application which employs the rvs code. https://github.com/yasukata/rvs/blob/6ec2d454ca0e0b405503897c1e711bd9dbc64dd9/rvs.c#L21-L26

yasukata / rvs

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