Real-Time Performance Analysis of Adaptive Link Rate Baoke Zhang, Karthikeyan Sabhanatarajan, Ann Gordon-Ross*, Alan D. George* This work was supported by the U.S. National Science Foundation The Energy Efficient Internet Project High-performance Computing & Simulation Research Lab ECE Department, University of Florida, Gainesville * Also affiliated with NSF Center for High Performance Reconfigurable Computing Joseph Antoon - Speaker 1

2 Introduction INTERNET

Introduction Connected edge devices account for 2% of the total power consumed in the US [EPA-06] – 130 TWh/Year – 1 single-unit nuclear power plant outputs 8 TWh/Year – Translates to 16 single-unit nuclear power plants! 3

Introduction Ethernet links – As they grow faster… – They eat more power! But, this corresponds to data capacity, right? 1Gbps +4W 100Mbps 10Gbps +16W 4

Introduction Wrong! Average traffic has 5% utilization 10Gbps +16W (Actually needed) Wasted! 1Gbps +4W 100Mbps 5

Adaptive Link Rate Ethernet links rarely utilized Only need high capacity for short bursts Adaptive Link Rate – Use low link rate – During idle periods Time link utilization link waste 6

Adaptive Link Rate PHY Tx Buffer Rx Buffer Network MAC Network Interface Card 100M Uh oh, need more throughput! 1G 7

Can’t send packets while switching Long switching time interrupts connections Result: Performance hit! To MACFrom PC Drawbacks Tx Buffer 8

Switching costs energy Goal: Positive net energy consumption Result: Minimum time to stay in low rate! Drawbacks Switch Energy Saved Energy Link Rate 9

Goals How long to switch? – Previous work assumes 1-10ms How much energy to switch How long to stay in low rate? Solution: Build a prototype – Virtex II Pro Development Kit – RiceNIC-based architecture Goals 10

Modified RiceNIC Architecture CRCAddr Add CRC Flow Control Interface MIIM PHY PCI Interface MAC Core FIFO Tx Control FIFO Rx Control Control Policy MAC Control Unit 11 Determines when To change link rate Coordinates link rate change Generates synthetic traffic

Experiment MAC Handshake time – How long to coordinate switch PHY Register Time – How long to trigger rate change PHY Resynchronization time – How long to physically reset link PHY MAC 100M1G 12

Results – Average Times >700,000% Longer 13

Results – PHY Resync Time 14

Results – Switching Power Not too bad! But what about energy? 15

Results – Energy Why not just switch to 100M, then 10M? +< 10M ↔ 1G costs so much when… 16

Minimum Time in Low Link Rate 20.8 Assuming a switch time makes a big difference! 17

Conclusions First hardware prototype of an Adaptive Link Rate (ALR) enabled NIC Observed switching times much longer than previously assumed “Step down” method uses less energy than switching from 1Gbps than 10Mbps 18

Thank you for attending! Any Questions? 19