Host Load Trace Replay Peter A. Dinda Thesis Seminar 11/23/98

2 Outline Motivation for load trace playback Interaction with external load Example system Feedback issue

3 Load Traces for Benchmarking Distributed Systems Real Comparable and reproducible Think of a set of traces as analogous to a SPEC benchmark Usable in simulation and experimentation Currently: synthetic benchmarks Poissony process arrivals, power-law process run-times, multiplexing LTI characterizations (impulse responses, etc) Few comparisons

4 Interaction with External Load External load modulates applied load Other interactions are possible - human driven apps

5 Load Measurement Sample1h { Ready Queue Sample2 unknown sample rate f=2 Hz estimated exponential average, tau=5 s f=1 Hz KernelUser Trace File

6 Load Trace Replay h -1 Load Generator Trace File Load Measure “1.5 load for 1 second” => 100 % busy, 50% busy processes x% busy process alternates between random duration compute and sleep phases so that x% of time is spent in compute phases on unloaded machine Sample1h { Sample2 error - applied load measured load

7 Example One Hour Trace

8 Applied Load

9 Measured Load

10 Error

11 Combined View

12 Distribution of Errors

13 Closer Look

14 Feedback? Use error signal to better track the load trace h -1 Load Generator Load Measure error - h -1 + z Trace File x level

15 The Problem With Feedback Feedback would try to make SUM of applied load and external load in system track the load trace External Load h -1 Load Generator Load Measure error - h -1 + z Trace File x level Applied Load Effect of Combined Load

16 Making Feedback Work External Load h -1 Load Generator Load Measure error - h -1 + z Trace File x level Signal Separation Applied Load Effect of Combined Load Estimated Effect of Applied Load Estimated Effect of External Load Load Source Models

17 Conclusions Developed reasonable tool for load trace playback Identified feedback issue Thinking about signal separation