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mTCP : A Highly Scalable User-level TCP Stack for Multicore Systems

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  1. mTCP: A Highly Scalable User-level TCP Stack for Multicore Systems EunYoungJeong, Shinae Woo, Muhammad Jamshed, HaewonJeong SunghwanIhm*, Dongsu Han, and KyoungSoo ParkKAIST *Princeton University

  2. Needs for Handling Many Short Flows * Commercial cellular traffic for 7 daysComparison of Caching Strategies in Modern Cellular Backhaul Networks, MOBISYS 2013 Middleboxes- SSL proxies- Network caches End systems- Web servers 32K

  3. Unsatisfactory Performance of Linux TCP • Large flows: Easy to fill up 10 Gbps • Small flows: Hard to fill up 10 Gbps regardless of # cores • Too many packets: 14.88 Mpps for 64B packets in a 10 Gbps link • Kernel is not designed well for multicore systems Linux: 3.10.16 Intel Xeon E5-2690 Intel 10Gbps NIC Performance meltdown

  4. Kernel Uses the Most CPU Cycles Web server (Lighttpd) Serving a 64 byte file Linux-3.10 Performance bottlenecks 1. Shared resources 2. Broken locality 3. Per packet processing Bottleneck removed by mTCP 1) Efficient use of CPU cycles for TCP/IP processing  2.35x more CPU cycles for app 2) 3x ~ 25x better performance 83% of CPU usage spent inside kernel!

  5. Inefficiencies in Kernel from Shared FD 1. Shared resources • Shared listening queue • Shared file descriptor space File descriptor space Listening queue Linear search for finding empty slot Lock Core 1 Core 2 Core 0 Core 3 Per-core packet queue Receive-Side Scaling (H/W)

  6. Inefficiencies in Kernel from Broken Locality 2. Broken locality Interrupt handling core != accepting core accept()read()write() Interrupt handle Core 1 Core 2 Core 0 Core 3 Per-core packet queue Receive-Side Scaling (H/W)

  7. Inefficiencies in Kernel from Lack of Support for Batching 3. Per packet, per system call processing Application thread accept(), read(), write() User Inefficient per system call processing Kernel BSD socket LInuxepoll Frequent mode switchingCache pollution Kernel TCP Inefficient per packet processing Packet I/O Per packet memory allocation

  8. Previous Works on Solving Kernel Complexity Still, 78% of CPU cycles are used in kernel! How much performance improvement can we getif we implement a user-level TCP stack with all optimizations?

  9. Clean-slate Design Principles of mTCP • mTCP: A high-performance user-level TCP designed for multicore systems • Clean-slate approach to divorce kernel’s complexity Problems Our contributions 1. Shared resources 2. Broken locality Each core works independently • No shared resources • Resources affinity 3. Lack of support for batching Batching from flow processing from packet I/O to user API Easily portable APIs for compatibility

  10. Overview of mTCP Architecture Core 0 Core 1 1 ApplicationThread 1 ApplicationThread 0 2 3 mTCP socket mTCPepoll mTCPthread 0 mTCPthread 1 User-level User-level packet I/O library (PSIO) NIC device driver Kernel-level • [SIGCOMM’10] PacketShader: A GPU-accelerated software router, http://shader.kaist.edu/packetshader/io_engine/index.html Thread model: Pairwise, per-core threading Batching from packet I/O to application mTCP API: Easily portable API (BSD-like)

  11. 1. Thread Model: Pairwise, Per-core Threading ApplicationThread 1 ApplicationThread 0 mTCP socket mTCPepoll mTCPthread 0 mTCPthread 1 Per-core listening queue User-level packet I/O library (PSIO) User-level Per-core file descriptor Kernel-level Device driver Core 0 Core 1 Per-core packet queue Symmetric Receive-Side Scaling (H/W)

  12. From System Call to Context Switching < mTCP Linux TCP higher overhead Application Thread Application thread User System call Context switching Kernel BSD socket LInuxepoll mTCP socket mTCPepoll Kernel TCP mTCPthread Batching to amortizecontext switch overhead User-level packet I/O library Packet I/O NIC device driver

  13. 2. Batching process in mTCP thread Application thread Socket API accept() epoll_wait() connect() write() close() Connect queue Write queue Close queue (7) Accept queue Event queue mTCP thread TX manager SYN S S/A RST FIN F/A Rx manager TX manager Control list Control list Internal event queue ACK list ACK list SYN ACK Data list Data list Data Payload handler (8) Rx queue Tx queue

  14. 3. mTCP API: Similar to BSD Socket API • Two goals: Easy porting + keeping popular event model • Ease of porting • Just attach “mtcp_” to BSD socket API • socket() mtcp_socket(), accept() mtcp_accept(), etc. • Event notification: Readiness model using epoll() • Porting existing applications • Mostly less than 100 lines of code change

  15. Optimizations for Performance • Lock-free data structures • Cache-friendly data structure • Hugepages for preventing TLB missing • Efficient TCP timer management • Priority-based packet queuing • Lightweight connection setup • …… Please refer to our paper 

  16. mTCP Implementation • 11,473 lines (C code) • Packet I/O, TCP flow management, User-level socket API, Event system library • 552 lines to patch the PSIO library • Support event-driven packet I/O: ps_select() • TCP implementation • Follows RFC793 • Congestion control algorithm: NewReno • Passing correctness test and stress test with Linux TCP stack

  17. Evaluation • Scalability with multicore • Comparison of performance of multicore with previous solutions • Performance improvement on ported applications • Web Server (Lighttpd) – Performance under the real workload • SSL proxy (SSL Shader, NSDI 11) – TCP bottlenecked application

  18. Multicore Scalability Linux: 3.10.12 Intel Xeon E5-2690 32GB RAM Intel 10Gbps NIC Inefficient small packet processing in Kernel Shared fd in process Shared listen socket * [LINUX3.9] https://lwn.net/Articles/542629/* [OSDI’12] MegaPipe: A New Programming Interface for Scalable Network I/O, Berkeley 64B ping/pong messages per connection Heavy connection overhead, small packet processing overhead 25x Linux, 5xSO_REUSEPORT*[LINUX3.9], 3xMegaPipe*[OSDI’12]

  19. Performance Improvement on Ported Applications Web Server (Lighttpd) • Real traffic workload: Static file workload from SpecWeb2009 set • 3.2x faster than Linux • 1.5x faster than MegaPipe SSL Proxy (SSLShader) • Performance Bottleneck in TCP • Cipher suite1024-bit RSA, 128-bit AES, HMAC-SHA1 • Download 1-byte object via HTTPS • 18% ~ 33% better on SSL handshake

  20. Conclusion • mTCP: A high-performing user-level TCP stack for multicore systems • Clean-slate user-level design to overcome inefficiency in kernel • Make full use of extreme parallelism & batch processing • Per-core resource management • Lock-free data structures & cache-aware threading • Eliminate system call overhead • Reduce context switch cost by event batching • Achieve high performance scalability • Small message transactions: 3x to 25x better • Existing applications: 33% (SSLShader) to 320% (lighttpd)

  21. Thank You Source code is available at http://shader.kaist.edu/mtcp/https://github.com/eunyoung14/mtcp