mTCP enables high-performance userspace TCP/IP stacks by bypassing the kernel and reducing system call overhead. It was shown to achieve up to 25x higher throughput than Linux for short flows. The document discusses porting the iperf benchmark to use mTCP, which required only minor changes. Performance tests found that mTCP-ified iperf achieved similar throughput as Linux iperf for different packet sizes, demonstrating mTCP's ability to easily accelerate networking applications with minimal changes. The author concludes mTCP is a simple and effective way to improve TCP performance but notes that for full-featured stacks, a system like NUSE may be preferable as it can provide the high performance of userspace stacks while supporting the full functionality of kernel

1. mTCP 使ってみた
Userspace TCP/IP stack for PacketShader I/O
engine
Hajime Tazaki
High-speed PC Router #3
2014/5/15

2. • PacketShader ファミリ (@ KAIST)
• ユーザ空間スタック(kernel bypass)
• w/ DPDK, PacketShader I/O, netmap
• 種々の高速化手法 (Fast Packet I/O,
affinity-accept, RSS, etc)を利用
• Short Flow:Linuxより25倍高速
mTCP とは
2
[mTCP14] Jeong et al., mTCP: A Highly Scalable User-level TCP Stack for
Multicore Systems, USENIX NSDI, April, 2014

3. `
名前。。。
3

4. Why Userspace Stack ?
• Problems
• Lack of connection locality
• Shared file descriptor space
• Inefficient per-packet processing
• System call overhead
• kernel stack performance saturation
4
[mTCP14] Jeong et al., mTCP: A Highly Scalable User-level TCP Stack for
Multicore Systems, USENIX NSDI, April, 2014

5. カーネルスタックの性能
5
アプリはほとんどCPU使
えていない
複数コアの利用効率悪い
[mTCP14] Jeong et al., mTCP: A Highly Scalable User-level TCP Stack for
Multicore Systems, USENIX NSDI, April, 2014

6. mTCP Design
6
[mTCP14] Jeong et al., mTCP: A Highly Scalable User-level TCP Stack for
Multicore Systems, USENIX NSDI, April, 2014

7. • パケットバッチング (ps I/O engine)
• システムコール回数減少
• コンテキストスイッチも減少
• CPUまたぎ極小化
mTCP Design
7

8. mTCP Design (cont’d)
8
[mTCP14] Jeong et al., mTCP: A Highly Scalable User-level TCP Stack for
Multicore Systems, USENIX NSDI, April, 2014

9. Application Modification
9
• BSD風Socket, epoll風 mux/demux
• 少量の修正で既存アプリ利用可能
• lighttpd (65 / 40K LoC)
• ab (531 / 68K LoC)
• SSL Shader (43 / 6.6K LoC)
• WebReplay (81 / 3.3K LoC)

10. 10
mTCP 性能
(64B ping-pong transaction)
[mTCP14] Jeong et al., mTCP: A Highly Scalable User-level TCP Stack for
Multicore Systems, USENIX NSDI, April, 2014
x25 Linux
x5 SO_REUSEPORT
x3 MegaPipe

11. `
mTCPお試し
11

12. • https://github.com/eunyoung14/
mtcp
• Q1: iperf を mTCP 化(簡単?)
• Q2: iperf 速くなるの?
さわってみた
12

13. Porting iperf for mTCP
• socket () => mtcp_socket ()
• LD_PRELOAD なライブラリでOK
かも。
13

14. 14
https://github.com/thehajime/iperf-2.0.5-mtcp

15. Performance
• PC0
• CPU: Xeon E5-2420 1.90GHz (6core)
• NIC: Intel X520
• Linux 2.6.39.4 (ps_ixgbe.ko)
• PC1
• CPU: Core i7-3770K 3.50GHz (8core)
• NIC: Intel X520-2
• Linux 3.8.0-19 (ixgbe.ko)
15
PC0: mTCP-ed iperf PC1: vanilla Linux

16. 0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
64 256 1024 2048 4096 8192
Goodput(Gbps)
Packet Size (bytes)
SendBuffer = 102400 (bytes)
MTCP
Linux
PacketSize - Goodput (Gbps)
16
mTCP: ほぼ同一
Packet Size は
write(mtcp_write)の
length
system call batching の
影響で高速化

17. Buffer Size - Goodput (Gbps)
17
0
0.5
1
1.5
2
2.5
2048 10240 51200 102400 204800 512000 1024000
Goodput(Gbps)
Buffer Size (bytes)
Packet size = 64 byte
MTCP
Linux
mTCP:調査中。。。
mTCP: Send Buffer configuration
Linux: wmem_max configuration

18. Summary
18
• パケット長によらず (1.6 Gbps)
• 単一コネクションなの。。
• 50行くらいの変更で利用可能 !
• 簡単に悪名高き iperf 高速化可能!

19. Discussion
19
• 複雑なものはユーザスペースへ
• マイクロカーネル ?
• システム入れ替え不要
• かつパフォーマンスも向上
Application
BSD Socket
network stack
NIC
Application
network stack
NIC
network
channel
user
kernel

20. • Kernel Bypass = Shortcut
• 省略された機能どうすんの ?
• only v4 ? udp ?
• ルーティングテーブル ?
• middlebox にしたら Quaggaとか?
Discussion (cont’d)
20

21. Library OS
21
• Library Operating System (LibOS)
• アプリケーションが選択可能なOS
• End-to-End principle (on OS?)
• rump[1], MirageOS[2], Drawbridge[3]
• ネットワークスタックだけはもう
ユーザスペースでいいんじゃね?[1] Kantee. Rump file systems: Kernel code reborn, USENIX ATC 2009.
[2] Madhavapeddy et al., Unikernels: library operating systems for the cloud ASPLOS 2013
[3] Porter et al., Rethinking the library OS from the top down. ASPLOS 2011
ARP
Qdisc
TCP UDP DCCP SCTP
ICMP IPv4IPv6
Netlink
BridgingNetfilter
IPSec Tunneling
Kernel layer
Heap Stack
memory
Virtualization Core
layer
ns-3 (network simulation core)
POSIX layer
Application
(ip, iptables, quagga)
bottom halves/rcu/
timer/interrupt
struct net_device
DCE
ns-3
applicati
on
ns-3
TCP/IP
stack

22. • Network Stack in
Userspace (NUSE)
• Direct Code Execution
• liblinux.so (latest)
• libfreebsd.so (10.0.0)
• カーネル実装されたも
のを全てライブラリ化
• 高機能化
• 高速化 ?
An implementation of LibOS
22
NUSE: Network Stack in Userspace
Hajime Tazaki1
and Mathieu Lacage2
,
1
NICT, Japan 2
France
Summary
Network Stack in Userspace (NUSE)
I A framework for the userspace execution of network stacks
I Based on Direct Code Execution (DCE) designed for ns-3 network simulator
I Supports multiple kinds and versions of network stacks implemented for kernel-space (currently net-next
Linux, freebsd.git are supported)
I Introduces the distributed validation framework in a single controller (thanks to ns-3).
I Transparent to existing codes (no manual patching to network stacks)
Problem Statement on Network Stack Development
Kernel-space
Network Stack
Implementation
Userspace
Network Stack
Implementation
hard to deploy
Existing Implementation
is desirable
Userspace implementation
is desirable
- implementing network stack from scratch
is not realistic (620K LOC in ./net-next/net/).
- needs to validate the interoperatbility again!
Infinite Loop on
Network Stack Development
The Architecture
(kernel-space)
Network Stack
Code
Shared
Library
Userspace
Program
compile dynamic-
link
I Kernel network stacks are compiled to shared library and linked to applications.
I Unmodified application codes (userspace) and network stack (kernel-space) are usable.
(Host) kernel
process
apps (socket/syscall)
NUSE bottom-half
(Guest) kernel
network stack
NUSE top-half
user-space
kernel-space
library
{
I Top-half provides a transparent interface to applications with system-call redirection.
I Bottom-half provides a bridge between userspace network stack and host operating
system.
Call trace via NUSE with Linux network stack:
(gdb) bt ---------------
#0 sendto () at ../sysdeps/unix/syscall-template.S:82 Host OS
#1 ns3::EmuNetDevice::SendFrom () at ../src/emu/model/emu-net-device.cc:913 Raw socket
#2 ns3::EmuNetDevice::Send () at ../src/emu/model/emu-net-device.cc:835 ---------------
#3 ns3::LinuxSocketFdFactory::DevXmit () at ../model/linux-socket-fd-factory.cc:297 NUSE
#4 sim_dev_xmit () at sim/sim.c:290 bottom half
#5 fake_ether_output () at sim/sim-device.c:165
#6 arprequest () at freebsd.git/sys/netinet/if_ether.c:271 ---------------
#7 arpresolve () at freebsd.git/sys/netinet/if_ether.c:419
#8 fake_ether_output () at sim/sim-device.c:89 freebsd.git
#9 ip_output () at freebsd.git/sys/netinet/ip_output.c:631 network stack
#10 udp_output () at freebsd.git/sys/netinet/udp_usrreq.c:1233 layer
#11 udp_send () at freebsd.git/sys/netinet/udp_usrreq.c:1580
#12 sosend_dgram () at freebsd.git/sys/kern/uipc_socket.c:1115 ---------------
#13 sim_sock_sendmsg () at sim/sim-socket.c:104 NUSE
#14 sim_sock_sendmsg_forwarder () at sim/sim.c:88 top half
#15 ns3::LinuxSocketFdFactory::Sendmsg () at ../model/linux-socket-fd-factory.cc:633 ---------------
#16 ns3::LinuxSocketFd::Sendmsg () at ../model/linux-socket-fd.cc:76 syscall
#17 ns3::LinuxSocketFd::Write () at ../model/linux-socket-fd.cc:44 emulation
#18 dce_write () at ../model/dce-fd.cc:290 layer
#19 write () at ../model/libc-ns3.h:187 ---------------
#20 main () at ../example/udp-client.cc:34 application
#21 ns3::DceManager::DoStartProcess () at ../model/dce-manager.cc:283 ---------------
#22 ns3::TaskManager::Trampoline () at ../model/task-manager.cc:250 ns-3 DCE
#23 ns3::UcontextFiberManager::Trampoline () at ../model/ucontext-fiber-manager.cc:1 scheduler
#24 ?? () from /lib64/libc.so.6 ---------------
#25 ?? ()
The kernel network stack code is transparently integrated into NUSE framework without any modifications into original one.
Experience
Linux (Host)
Apps
NIC
1) Linux native stack
Linux (Host)
vNIC
ns3-core
NUSE bottom-
half
linux net-next
Apps
NUSE top-half
NIC
2) NUSE with Linux stack
Linux (Host)
vNIC
ns3-core
Apps
NUSE bottom-
half
freebsd.git
NUSE top-half
NIC
3) NUSE with FreeBSD stack
I A UDP simple socket-based traffic generator is used with three different scenarios.
I The development tree version of Linux and FreeBSD kernel is encapsulated by NUSE without modifying the
application and host network stacks.
0
5000
10000
15000
20000
1 2 3 4 5
UDPpacketgeneratingperformance(pps)
Time (sec)
1) native
2) Linux NUSE
3) Freebsd NUSE
I Linux NUSE shows a different behavior with Linux native stack: current timer implementation in NUSE is
simplified and not enough to emulate native one accurately.
I Native and FreeBSD NUSE show a similarity in the UDP packet generation.
Possible Use-Cases
network stack
process
NUSE
(Guest) network
stack
user-space
kernel-space
NIC
bypassed
(raw sock/tap
/netmap)
I Application embedded network stacks deployment (e.g., Firefox + NUSE Linux + mptcp.).
I No required kernel stack replacement with bypassing the host network stack.
network stack
process
NUSE
network
stack X
user-space
kernel-space
NIC
Multiple
Network Stack
Instances
process
NUSE
network
stack Y
process
NUSE
network
stack Z
NIC
network stack
ns-3
I Multiple network stacks debugging via ns-3 network simulator.
I Validation platform across the distributed network entities (like VM multiplexing) with a simple controllable
scenario.
Related Work
I Userspace network stack porting: Network Simulation Cradle [6], Daytona [9], Alpine [4], Entrapid [5],
MiNet [3]
Need of manual patching, resulting the difficulties of latest version tracking.
I Virtual machines, operating systems: (KVM [8]/Linux Container [1]/User-mode Linux [2])
High-level transparency introduces the broader compatibility of codes (application, network stack), but
unnecessary workload for the application execution.
I In-kernel userspace execution support: Runnable Userspace Meta Program (RUMP) [7]
No manual patching (already integrated NetBSD), but lack of integrated operation.
Future Directions
I Userspace binary emulation should
I More useful example with unavailable features of current network stacks (e.g., mptcp)
I Seek the performance improvement with userspace network stack by utilizing multiple processors.
I Promote to merge Linux/FreeBSD main-tree as a general framework.

23. Next Steps
• net-next-sim (liblinux.so)
• Linuxと同等機能な userspace stack
• make menuconfig で必要なものだけ
• (work-in-progress)
23

24. まとめ
• mTCP 簡単・高速 !
• (Packet I/O高速化だけなら)
• 速ければいいのか ?
• 速くて、高機能で、自由度も高く!
24

25. References
• Jeong et al., mTCP: A Highly Scalable User-level TCP
Stack for Multicore Systems, USENIX NSDI, April, 2014
• iperf mTCP version
• https://github.com/thehajime/iperf-2.0.5-
mtcp
• PacketShader I/O engine mod (X520)
• https://github.com/thehajime/mtcp
• Direct Code Execution (liblinux.so)
• https://github.com/direct-code-execution/
net-next-sim
25

26. • to Linux 3.8.0
• 基本問題なし
• ARP/Static Route をファイルに設定
• to macosx (10.9.2) TCPv4 (iperf)
• static route /32 で設定できない..
• でもちゃんとEstablish になる !
相互接続関連
26