1 Characterization and Evaluation of TCP and UDP-based Transport on Real Networks Les Cottrell Sun SuperG Spring 2005, April, Partially funded by DOE/MICS Field Work Proposal on Internet End-to-end Performance Monitoring (IEPM)

2 Overview What’s the problem getting high performance data transport on high speed networks Possible solutions –Software –Hardware Measurements and comparisons: –Offloads, OS’, jumbos, parallel streams, NICs SC2005 Bandwidth Challenge 101 Gbits/s –Some results –What was special Conclusions Who needs it anyway?

3 What’s the problem? Standard TCP recovers very slowly from a congestion event (perceived packet loss): –To remove the need to wait to acknowledge each packet, the sender fills the pipe with a “window” of unacknowledged packets –To fill a 10Gbps pipe between California and Switzerland requires a window of 137,500 * 1500 Byte packets –If sees congestion reduces throughput (window) by factor 2 (Multiplicative Decrease) –Then only adds 1 packet to window for each acknowledgement (Additive Increase) –OK for low speed 64kbps links of original Internet –BUT: at 10Gbps, RTT=165msec it takes many hours to recover –So need losses of << 1 in 10^14!! Sunnyvale-Geneva RTT (165ms), 1500Byte MTU, stock TCP Src Rcv ACK ~RTT

4 Possible solutions Jumbo frames (1500Bytes std => 9000Bytes), factor of 6 improvement in recovery rate –Not an IEEE standard –May break some UDP applications –Not supported on many LANs Sender mods only, HENP model is few big senders, lots of smaller receivers –Simplifies deployment, only a few hosts at a few sending sites –So no Dynamic Right Sizing (DRS) at receiver Runs on production nets (hard to deploy a new Internet) –No router mods (XCP/ECN)

5 Parallel streams Use multiple parallel TCP streams for an application such as FTP –No modifications to kernel –Improves TCP by ~ number of streams –Very effective –But Maybe unfair to others, especially for large numbers of streams Have to optimize both the window size AND the number of streams simultaneously, and that may change from day to day or even hour to hour on congested networks

6 Software Transports Advanced TCP stacks – being developed on Linux –To overcome AIMD congestion behavior of Reno based TCPs, while preserving stability, and fairness … –BUT: SLAC “datamover” are all based on Solaris, while advanced TCPs currently are Linux only SLAC production systems people concerned about non-standard kernels, ensuring TCP patches keep current with security patches for SLAC supported Linux version So also very interested in transport that runs in user space (no kernel mods) –Evaluate UDT (reliable UDP transport) from UIC folks

7 Reno single stream Low performance on fast long distance paths –AIMD (add a=1 pkt to cwnd / RTT, decrease cwnd by factor b=0.5 in congestion) –Net effect: recovers slowly, does not effectively use available bandwidth, so poor throughput Remaining flows do not take up slack when flow removed Congestion has a dramatic effect Recovery is slow Multiple streams increase recovery rate SLAC to CERN RTT increases when achieves best throughput

8 New TCP stacks Adjust recovery (faster than linear) & back off (less dramatic) –Only available on Linux today, still in development One of the best performers is HTCP –Throughput is high –Big effects on RTT when achieves best throughput –Flows share equally, stable, Appears to need >1 flow to achieve best throughput Two flows share equally SLAC-CERN

9 Hardware Assists For 1Gbits/s paths, cpu, bus etc. not a problem For 10Gbits/s they are important NIC assistance to the CPU is becoming popular –Checksum offload –Interrupt coalescence –Large send/receive offload (LSO/LRO) –TCP Offload Engine (TOE) Several vendors for 10Gbits/s NICs, at least one for 1Gbits/s NIC But currently restricts to using NIC vendor’s TCP implementation Most focus is on the LAN –Cheap alternative to Infiniband, MyriNet etc.

10 10Gbps tests Sunfire vx0z, Linux & Solaris 10, Chelsio & Neterion Back-to-back (LAN) testing at SLAC SNV to LA At SC2004 using two 10Gbps dedicated paths between Pittsburgh and Sunnyvale –Using Solaris 10 (build 69) and Linux 2.6 –On Sunfire Vx0z (dual & quad 2.4GHz 64 bit AMD Opterons) with PCI-X 133MHz 64 bit –Only 1500 Byte MTUs Achievable performance limits (using iperf) –Reno TCP (multi-flows) vs UDTv2, –TOE (Chelsio) vs no TOE (Neterion(S2io))

11 Results - Summary UDT limit was ~ 4.45Gbits/s –Cpu limited TCP Limit was about 7.5±0.07 Gbps, regardless of: –Whether LAN (back to back) or WAN Gating factor=PCI-X 133Mhz –Raw bandwidth 8.53Gbps –But transfer broken into segments to allow interleaving –E.g. with max memory read byte count of 4096Bytes with Intel Pro/10GbE LR NIC limit is 6.83Gbits/s One host with 4 cpus & 2 NICs sent 11.5±0.2Gbps to two dual cpu hosts with 1 NIC each Two hosts to two hosts (1 NIC/host) 9.07Gbps goodput forward & 5.6Gbps reverse

12 CPU Utilization Receiver needs 20% less CPU than sender for high throughput For Neterion with LSO & Linux: Sender appears to use more CPU than receiver as the throughput increases Single stream limited by 1.8GHz CPU

13 Effect of Jumbos Throughput SLAC-CENIC LA (1 stream, 2MB window with LSO Neterion(S2io)/Linux): –1500B MTU 1.8 Gbps –9000B MTU 6 Gbps Sender CPU: GHz/Gbps (single stream with LSO Neterion/Linux): –1500B MTU = 0.5 ± 0.13 GHz/Gbps (single sender to single receiver, need to extend to multi-receivers) –9000B MTU = 0.3 ± 0.07 GHz/Gbps –Factor 1.7 improvement For Neterion with LSO &Linux on WAN, Jumbos have a huge effect on performance and also improve CPU utilization

14 Effect of LSO v20z 1.8GHz, Linux 2.6, S2io, 2 streams SLAC to Caltech, 8MB window: –With LSO: 7.4Gbits/s, –Without LSO: 5.4Gbits/s, LAN (3 streams, 164KB window) –Solaris => Linux: 6.4Gbps (No LSO support in Solaris 10 at the moment) –Linux => Solaris-10: 4.8Gbps (LSO turned off sender) –Linux => Solaris-10: 7.54Gbps (LSO turned on) For Neterion with Linux on LAN LSO improves CPU utilization by a factor of 1.4. If one is CPU limited this will also improve throughput. 1 stream

15 Solaris vs Linux Send from one to the other single stream Compare send from Linux Neterion + LSO with send from Solaris 10 without LSO –LSO support in Solaris coming soon With one stream Solaris sender sends faster Sol slightly better GHz/Gbps GHz/Gbps: Solaris ; Linux

16 Solaris vs Linux multi- streams When optimize for multiple streams, Linux + LSO sender is better 1MB 2MB 4MB Solaris without LSO performs poorly with multiple streams (LSO or OS related?) –Its GHz/Gbps is poorer than Linux+LSO for multiple streams LAN MTU: 9400B S2io 7.5Gbps 6.4Gbps

17 Chelsio Chelsio to Chelsio (TOE) With 2.4GHz V20zs from Pittsburgh to SNV 1500Byte MTUs Reliably able to get Gbps (16 streams) GHz/Gbps Chelsio(MTU=1500B) ~ Neterion (9000B) Chelsio(TOE)

18  Joint Caltech, SLAC, FNAL, CERN, UF, SDSC, BR, KR, ….  Gbps waves to HEP on show floor  Bandwidth challenge: aggregate throughput of Gbps  FAST TCP SC2004: Tenth of a Terabit/s Challenge

19 Bandwidth Challenge Large collaboration of academia and industry Took a lot of “wizards” to make it work >100 Gbps aggregate The prize!

20 What was special? End-to-end application-to-application, single and multi- streams (not just internal backbone aggregate speeds) TCP has not run out of stream yet, scales from modem speeds into multi-Gbits/s region –TCP well understood, mature, many good features: reliability etc. –Friendly on shared networks New TCP stacks only need to be deployed at sender –Often just a few data sources, many destinations –No modifications to backbone routers etc –No need for jumbo frames Used Commercial Off The Shelf (COTS) hardware and software

21 What was Special 2/2 Raise the bar on expectations for applications and users –Some applications can use Internet backbone speeds –Provide planning information The network is looking less like a bottleneck and more like a catalyst/enabler –Reduce need to colocate data and cpu –No longer ship literally truck or plane loads of data around the world –Worldwide collaborations of people working with large amounts of data become increasingly possible

22 Conclusions Todays limit (PCI-X) is about 7.5Gbits/s Jumbos can be a big help LSO is helpful (Neterion) For best throughput Linux+LSO sender better Without LSO Solaris provides more throughput –Need to revisit when Solaris supports LSO –Also untangle Solaris  Linux Solaris without LSO has problems with multiple streams TOE (Chelsio) allows one to avoid 9000Byte MTUs –Need further study on 9000B MTU for Chelsio –Try Chelsio on Solaris Longer paths (trans-Atlantic) New buses (PCI-Express)

23 Conclusions Need testing on real networks –Controlled simulation & emulation critical for understanding –BUT need to verify, and results can look different than expected Most important for transoceanic paths UDT looks promising, still needs work for > 6Gbits/s Need to evaluate various offloads (TOE, LSO...) New buses (PCI-X 266Mhz and PCI-Express important, need NICs/hosts to support then evaluate

24 Who needs it? HENP – current driver –Multi-hundreds Mbits/s and Multi TByte files/day transferred across Atlantic today SLAC BaBar experiment already has a PByte stored –Tbits/s and ExaBytes (10 18 ) stored in a decade Data intensive science: –Astrophysics, Global weather, Bioinformatics, Fusion, seismology… Industries such as aerospace, medicine, security … Future: –Media distribution Gbits/s=2 full length DVD movies/minute 100 Gbits/s is equivalent to –Download Library of Congress in < 14 minutes –Three full length DVDs in a second Will sharing movies be like sharing music today?

25 Acknowledgements Gary Buhrmaster*, Parakram Khandpur*, Harvey Newman c, Yang Xia c, Xun Su c, Dan Nae c,Sylvain Ravot c, Richard Hughes-Jones m, Michael Chen +, Larry McIntosh s, Frank Leers s, Leonid Grossman n, Alex Aizman n SLAC*, Caltech c, Manchester University m, Chelsio +, Sun s, Neterion(S2io) n

26 Further Information Web site with lots of plots & analysis – Inter-protocols comparison (Journal of Grid Comp, PFLD04) – SC2004 details –www-iepm.slac.stanford.edu/monitoring/bulk/sc2004/

27 From LS Off MTU Byte s Median Thru GbpsIQR GHz/ GbpsIQR Linux On Linux On Linux Off Solaris Off Solaris Off

28 When will it have an impact ESnet traffic doubling/year since 1990 SLAC capacity increasing by 90%/year since 1982 –SLAC Internet traffic increased by factor 2.5 in last year International throughput increase by factor 10 in 4 years So traffic increases by factor 10 in 3.5 to 4 years, so in: –3.5 to 5 years 622 Mbps => 10Gbps –3-4 years 155 Mbps => 1Gbps –3.5-5 years 45Mbps => 622Mbps : –100s Gbits for high speed production net end connections –10Gbps will be mundane for R&E and business –Home broadband: doubling ~ every year, 100Mbits/s by end of decade –Aggressive Goal: 1Gbps to all Californians by 2010 Throughput Mbits/s Throughput from US