Progressive profiling: A methodology based on profile propagation and selective profile collection.
详细信息
文摘
In recent years, Profile-Based Optimization (PBO) has become a key technique in program optimization. In PBO, the optimizer uses information gathered during previous program executions to guide the optimization process. Even though PBO has been implemented in many research systems and some software companies, there has been little research on how to make PBO effective in practice.;In today's software industry, one major hurdle in applying PBO is the conflict between the need for high-quality profiles and the lack of time for long profiling runs. For PBO to be effective, the profile needs to be representative of how the users or a particular user runs the program. For many modern applications that are large and interactive, it takes a significant amount of time to collect high-quality profiles. This problem will only become more prominent as application programs grow more complex. A lengthy profiling process is especially impractical in software production environments, where programs are modified and rebuilt almost daily. Without enough time for extensive profiling runs, the benefit from applying PBO is severely limited. This in turn hampers the interest in running PBO and increases the dependency on hand tuning in software development and testing.;In order to obtain high-quality profiles in a software production environment without lengthening the daily build cycle, we seek to change the current practice where a new profile must be generated from scratch for each new program version. Most of today's profiles are generated for a specific program version and become obsolete once the program changes. We propose progressive profiling , a new profiling methodology that propagates a profile across program changes and re-uses it on the new version. We use static analysis to generate a mapping between two versions of a binary program, then use the mapping to convert an existing profile for the old version so that it applies to the new version. When necessary, additional profile information is collected for part of the new version to augment the propagated profile. Since the additional profile collection is selective, we avoid the high expense of re-generating the entire profile. With progressive profiling, we can collect profile information from different generations of a program and build a high-quality profile through accumulation over time, despite frequent revisions in a software production environment.;We present two different algorithms for matching binary programs for the purpose of profile propagation, and use common application programs to evaluate their effectiveness. We use a set of quantitative metrics to compare propagated profiles with profiles collected directly on the new versions. Our results show that for program builds that are weeks or even months apart, profile propagation can produce profiles that closely resemble directly collected profiles. To understand the potential for time saving, we implement a prototype system for progressive profiling and investigate a number of different system models. We use a case study to demonstrate that by performing progressive profiling over multiple generations of a program, we can save a significant amount of profiling time while sacrificing little profile quality.