Full text
| |
| Author(s): |
Divino César Soares Lucas
Total Authors: 1
|
| Document type: | Master's Dissertation |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Instituto de Computação |
| Defense date: | 2013-09-04 |
| Examining board members: |
Guido Costa Souza de Araújo;
Fernando Magno Quintão Pereira;
Sandro Rigo
|
| Advisor: | Guido Costa Souza de Araújo; Edson Borin |
| Abstract | |
Virtual machines are systems that aim to eliminate the compatibility gap between two, possible distinct, interfaces, thus enabling them to communicate. This way, acting like a mediator, the VM lies at an important position that enables it to foster innovative solutions for many problems. Such systems usually rely on emulation techniques, such as interpretation and dynamic binary translation, to execute guest application code. In order to select the best emulation technique for each code segment, the VM typically needs to predict whether the cost of compiling the code overcome its future execution time. This problem, in the common case, reduce to predicting if the given code region will be frequently executed or not, a problem called Hot Code Prediction. Generally, if the predictor flags a given code region as hot the VM instantly takes the decision to compile it. However, a problem came out from this strategy, the predictor response is only a decision made by means of a heuristic and thus it can be incorrect. Whenever the predictor flags a code region that will be infrequently executed (cold code) as hot code, we say that it is doing a hotness misprediction. Whenever a misprediction happens it means that the technique the VM will use to emulate the code will not have its cost amortized by executing the optimized code and thus the VM will, in fact, spend more time executing its own code rather than the guest application code. In this work we measure the impact of hotness mispredictions in a VM emulating several kinds of applications. In our analysis we evaluate the threshold-based hot code predictor, a technique commonly used to predict hot code fragments. To do so we developed a mathematical model to simulate the behavior of such predictor and we use it to estimate the impact of mispredictions in several benchmarks. We show that this predictor frequently mispredicts the code hotness and as a result the VM emulation performance becomes dominated by miscompilations. Moreover, we show how the threshold choice can affect the number of mispredictions and how this impacts the VM performance. We also show how the compilation, interpretation and steady state execution cost of translated instructions affect the VM performance. At the end we show that using SPEC CPU 2006 benchmarks to measure the performance of a VM using the threshold-based predictor can lead to misleading results (AU) | |
| FAPESP's process: | 11/05028-5 - Algorithms and hardware support for design of efficient virtual machines |
| Grantee: | Divino César Soares Lucas |
| Support Opportunities: | Scholarships in Brazil - Master |