1. CSE 691: Energy-Efficient Computing Lecture 6 SHARING: distributed vs. local Anshul Gandhi 1307, CS building anshul@cs.stonybrook.edu

2. energy_routing paper

3. # servers

4. workload

5. softscale paper

6. 6 Goals of a data center Low response times Goal: T 95 ≤ 500 ms Performance 70% is wasted Goal: Minimize waste Power Load Time  BUSY: 200 W  IDLE: 140 W  OFF: 0 W Intel Xeon server

7. 7 Scalable data centers PerformancePower  BUSY: 200 W  IDLE: 140 W  OFF: 0 W Intel Xeon server Reactive: [Leite’10;Horvath’08;Wang’08] Predictive: [Krioukov’10;Chen’08;Bobroff’07] Setup cost 300 s 200 W (+more) Only if load changes slowly Load Time

8. 8 Problem: Load spikes Load Time x 2x

9. 9 Prior work Dealing with load spikes Spare servers [Shen’11;Chandra’03]  Over provisioning can be expensive Forecasting [Krioukov’10;Padala’09;Lasettre03]  Spikes are often unpredictable Compromise on performance [Urgaonkar’08;Adya’04;Cherkasova’02]  Admission control, request prioritization x Load Time 2x

10. 10 Our approach: SOFTScale No spare servers No forecasting Does not compromise on performance (in most cases) Can be used in conjunction with prior approaches x Load Time 2x

11. Closer look at data centers Always on Use caching tier to “pick up the slack” 11 Scalable

12. High-level idea OFF SETUP Load Time x 2x Dual purpose Leverage spare capacity 12 ON

13. Experimental setup PHP (CPU-bound) Memcached (memory-bound) Response time: Time for entry to exit Average response time: 200ms (with 20X variability) Goal: T 95 ≤ 500ms Apache 13

14. Experimental setup 14 8-core CPU 4 GB memory 4-core CPU 48 GB memory PHP (CPU-bound) Memcached (memory-bound) Apache

15. Results: Instantaneous load jumps 15 Load Time 50% 61% 10%  29% T 95 (ms) averaged over 5 mins baseline = provisioned for initial load

16. Conclusion 16 Problem: How to deal with load spikes? Prior work: Over provision, predict, compromise on performance Our (orthogonal) approach: SOFTScale  Leverages spare capacity in “always on” data tiers  Look at the whole system  Can handle a range of load spikes