Whew. The months tick by quickly these days. Back in October 2007, Red Hat released a service update which officially supported and exploited the IBM POWER6 systems. The Red Hat exploitation code had been worked on by LTC programmers from around the world - providing a Linux OS version that handily and easily provides very nice performance for enterprise customers in production mode.
The performance teams submitted a series of SPEC.org (see the Appendix in the white paper link below for the list) and single-system Linpack publishes at the time, which have since been reviewed, approved, and published. One of the things we really like to focus on is the "whole software stack" when performance is looked at. So a short white paper was written up to explain the various software pieces and how they were tuned. To me this is far more interesting than the bottom-line metrics and the various sparring leadership claims that bounce around the industry. 'Course, it's always fun to have those leadership claims while they last.
The paper - an interesting mix of marketing introductions and then some technical details - really is intended to focus on the basics of leveraging the platform specific compilers (IBM's XL C/C++ and Fortran compilers), platform specific tuned math libraries (ESSL), a Linux open source project called libhugetlbfs, MicroQuill's clever SmartHeap product, FDPR-pro - which I've posted on earlier, IBM's Java, all running examples on the IBM System p 570 system.
Following these activities and working with various customers and interested programmers, there's some interesting work going on with using the oprofile analysis tools on Linux - especially as a non-root user - and working on understanding edge cases where the performance of a workload isn't purely predictable and deterministic. What's interesting is the possible performance variability of a workload when memory being used by a program isn't regularly placed local to each executing core (a classic NUMA-type issue), especially in the case of varying page sizes supported by the Linux operating systems.
I'll post some examples of using oprofile in different ways this month, and also an example of a Fortran program which can show varying run-times and how to address that.
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