TECH : Delivering Sample-based PGO for PlayStation(R)4

Greg Bedwell & Robert Lougher
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Event: 2017 European LLVM Developers Meeting 

Users of the PlayStation(R)4 toolchain have a number of expectations from their development tools: good runtime performance is vitally important, as is the ability to debug fully optimized code. The team at Sony Interactive Entertainment have been working on delivering a Profile Guided Optimization solution to our users to allow them to maximize their runtime performance. First we provided instrumentation-based PGO which has been successfully used by a number of our users. More recently we followed this up by also providing a Sample-based PGO approach, built upon the work of and working together with the LLVM community, and integrated with the PS4 SDK's profiling tools for a simple and seamless workflow.

In this talk, we'll present real-world case-studies showing how the Sample-based approach compares with Instrumented PGO in terms of user workflow, runtime intrusion while profiling, and final runtime performance improvement. We'll show with the aid of real code examples how the performance results of Sample-based PGO are heavily impacted by the accuracy of the compiler's line table debugging information and how by improving the propagation of debug data in some transformations both the Sample-based PGO runtime performance results and the overall user experience of debugging optimized code have been improved, so that anyone implementing new transformations can take this into account, especially as debug information is increasingly being used by consumers other than traditional debuggers that rely on its accuracy.

Duration: 38 Minutes

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