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Implementing a Compiler based I/O prefetching system for Linux

Implementing a Compiler based I/O prefetching system for Linux. CS 15-712 Course Project Amit Kumar Manjhi Mahim Mishra. Introduction. For large scientific applications, working set often exceeds size of available physical memory

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Implementing a Compiler based I/O prefetching system for Linux

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  1. Implementing a Compiler based I/O prefetching system for Linux CS 15-712 Course Project Amit Kumar Manjhi Mahim Mishra

  2. Introduction • For large scientific applications, working set often exceeds size of available physical memory • Result: large page fault penalties for access to out-of-core data • Large performance hit when an in-core application becomes out-of-core • Remedy: Prefetch data!

  3. Performance w and w/o prefetch

  4. Prefetching Architecture • Compiler to analyze a program’s data usage and insert prefetch instructions • Other approaches: run-time analysis by the OS; hints provided by the programmer; explicit I/O management by the programmer • Kernel should provide non-blocking prefetch and release calls • Also, a user level run-time library that filters out unnecessary prefetch calls

  5. Pref. Architecture continued • Angela Demke Brown implemented this on Hector/Hurricane and SGI/IRIX • Compiler: set of SUIF passes • Tested her results with the NAS parallel benchmark suite • Highly regular code written in Fortran • Scalable data set

  6. Porting to Linux • Compiler: should be easily portable • Run Time Library: statically linked shared library that intercepts prefetch and release calls from the application and makes appropriate system calls • Kernel system call handlers which bring in a page and remove it asynchronously • Code very similar to Linux page fault code

  7. Linux Implementation Issues • Kernel hacking: time consuming for newbies. • Needs modification to basic Kernel data structures like task_struct, mm_struct etc. • Changes required in page fault and other memory management code for inter-operability and performance stats. • Also, test runs take a loooong time. Plus they can crash the kernel.

  8. Current Status • Compiler generated code working on Linux • Although the compiler still runs on IRIX • Run time layer: done • Kernel prefetch code: on it’s way. A preliminary version doesn’t crash, although correctness needs to be tested • Work ahead: • polish implementation • measure actual performance gains for apps.

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