Packet Coalescing for Dual-Mode Energy Efficient Ethernet: A Simulation Study Mehrgan Mostowfi School of Mathematical Sciences University of Northern Colorado Greeley, Colorado, USA mehrgan.mostowfi@unco.edu Slide 1 of 11 Packet Coalescing for Dual-Mode EEE
What is EEE? An IEEE Standard (ratified in 2010) [1] • Introduces a Low-Power Idle (LPI) mode to Ethernet links • Works as follows for 10 Gb/s and less: High transition times even for 10 Gb/s and less [2] . Would be magnified for 40 Gb/s and above. [1] IEEE P802.3az Energy Efficient Ethernet Task Force. [2] P. Reviriego, J. Hernandez, D. Larrabeiti, and J. Maestro, “Performance Evaluation of Energy Ecient Ethernet,” IEEE Communications Letters, vol. 13, pp. 697-699, September 2009. Slide 2 of 11 Packet Coalescing for Dual-Mode EEE
EEE for 40 Gb/s and above Two modes are introduced [1] • Deep Sleep: Identical to LPI • Fast Wake: - Does not yield any power savings - In sending side to keep the sender and receiver in alignment - Much faster transitions (Wakeup: 0.34 us vs. 5.50 us from DS) • Limits power savings to receive side only in practice Can Fast Wake effectively become a new low-power mode for EEE? A case can be made [2] • Only needs to send LPI signals Transition times would still be too high. [1] IEEE 802.3bj-2014 Amendment 2: Physical Layer Specications and Management Parameters for 100 Gb/s Operation Over Backplanes and Copper Cables,“ IEEE Computer Society, June 2014. [2] H. Barrass, “Options for EEE in 100G,” presentation at IEEE P802.3bj meeting, January 2012. Slide 3 of 11 Packet Coalescing for Dual-Mode EEE
Overcoming High Transition Times Packet Coalescing • Gather up a few packets, send in one burst • A sleep and wakeup transition for a number of packets • Time-based and Count-based • Has shown to be effective for EEE for 10 Gb/s and below [1] Packets arrive, Power coalesced Packet transmission Packet transmission Active (100%) Coalescing timer Fast expires, pkts in Wake buffer < S coal /2 Coalescing timer (70%) expires, pkts in Coalescing buffer ≥ S coal /2 begins Coalescing Coalescing Fast Wake Timer begins begins Packets arrive, expires, pkts coalesced in buffer ≥ S coal /2 Deep Fast Wake Timer Packets arrive, expires, pkts in Sleep coalesced buffer < S coal /2 (10%) T FtoD T AtoF T idle T FtoA T AtoD T coal T DtoA T AtoD T coal T DtoA T AtoF T idle T FtoA T AtoF T idle [1] K. Christensen, P. Reviriego, B. Nordman, M. Bennett, M. Mostowfi, and J. Maestro, “IEEE 802.3az: The Road to Energy Efficient Ethernet,” IEEE Communications Magazine, vol. 48, no. 11, pp. 50-56, November 2010. Slide 4 of 11 Packet Coalescing for Dual-Mode EEE
Simulation Model CSIM simulation library in C • A unidirectional EEE link with Active, FastWake, and Deep Sleep modes • Ethernet link was simulated by a CSIM server facility • A Finite State Machine (FSM) controlled the server • Some variables and timers in the FSM: Slide 5 of 11 Packet Coalescing for Dual-Mode EEE
The Finite State Machine Packet arrived RESET 5) -------------------- Packet arrived Buffer packet 7) -------------------- Buffer packet (Buffer empty) && ( DFlag == FALSE) 3) ------------------------- Set TT IMER to T AtoF Start TT IMER toFW TT IMER expired Fast 6) ------------------------- Packet arrived Wake Set FT IMER to T idle 1) ------------------- Start FT IMER Buffer packet (FT IMER expired) && ( FT IMER expired) && (Buffer is empty) (Buffer is not empty) 9) --------------------------- (Buffer empty) && 8) ------------------- Set TT IMER to T FtoD ( DFlag == TRUE) DFLag = ( # of packets in Start TT IMER 4) ------------------------- Active buffer < ( S coal /2) ) Set TT IMER to T AtoD Packet in buffer Start TT IMER Set TT IMER to T FtoA 2) --------------------- Start TT IMER Transmit packet TT IMER expired 16) --------------------- toDS Packet arrived ( CTimer Expired) || ((# of packets in buffer ≥ S coal ) 10) -------------------- 14) ----------------------------------------------------------------- Buffer packet DFLag = (# of packets in toA buffer < ( S coal /2) ) Set TT IMER to T DtoA Deep TT IMER expired Start TT IMER Packet arrived 11) ------------------------- 15) -------------------- Sleep Buffer packet (Packet arrived) && (Packet arrived) && (Buffer is empty) 12) -------------------- (Buffer is not empty) 13) ---------------------------- Buffer packet Buffer packet Set CT IMER to T coal Start CT IMER Slide 6 of 11 Packet Coalescing for Dual-Mode EEE
Experiments Performed on the Simulation Model • Link capacity: 40 Gb/s • Transition times: taken from the standard (closest in meaning) • Coalescing time Fast Wake: 3.00 us • Power consumptions: - Active and transitions: 100% (the peak power consumption) - Fast Wake: 70% - Deep Sleep: 10% • Two set of experiments: - Smooth Traffic: Poisson packet arrivals. - Bursty Traffic: Interrupted Poisson Process packet arrivals • Two coalescer sizes: - Small: In Deep Sleep coalesce 10 pkts or for 3.00 us - Large: In Deep Sleep coalesce 100 pkts or for 30.00 us Slide 7 of 11 Packet Coalescing for Dual-Mode EEE
Results – Poisson Traffic Coalescing brings the power consumption closer to ideal, compared to Deep Sleep Only and no coalescing Tradeoff: added per-packet delay Slide 8 of 11 Packet Coalescing for Dual-Mode EEE
Results – Bursty Traffic Similar results. Better consumption is the traffic is bursty (some of the coalescing is done already) Is the added delay significant? Slide 9 of 11 Packet Coalescing for Dual-Mode EEE
Conclusions and Future Work Conclusions: • Dual-Mode EEE can be an effective method of extending idle periods between packet arrivals in order to maximize the opportunity for sleeping. • The tradeoff, the increased packet delay, may be justifiable by the energy savings gained. Future Work: • The technical feasibility? (more EE than CS) • Other response variables? • Other tradeoffs? • Real traffic traces? Slide 10 of 11 Packet Coalescing for Dual-Mode EEE
Questions from the audience Thanks for listening. Any questions? Mehrgan Mostowfi School of Mathematical Sciences University of Northern Colorado Greeley, Colorado, USA mehrgan.mostowfi@unco.edu See the paper for more details Slide 11 of 11 Packet Coalescing for Dual-Mode EEE
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