The success of Altix systems in the high performance computing market are a very positive sign for both Linux and Itanium. Clearly, the popularity of large processor count Altix systems dispels any notions of whether Linux is a scalable OS for scientific applications. Linux is quite popular for HPC and will continue to remain so in the future, as it inherits the role that was filled by Tru64 and IRIX. One of the most impressive facts to come out of this interview is that kernel tweaks can yield a 20-30% performance boost. This is a very high figure and helps to show how much Linux has been improved over the past year and half, thanks to the investment of major OEMs and IP donors.
However, scientific applications have very different operating characteristics from commercial applications. Typically, much of the work in scientific code is done inside loops, whereas commercial applications, such as database or ERP software are far more branch intensive. This makes the memory hierarchy more important, particularly the latency to main memory. Whether Linux can scale well with a workload is an open question. However, there is no doubt that with each passing month, the scalability in such environments will improve. Unfortunately, SGI has no plans to move into this market, at this point in time. However, it would be very interesting to see how the low latency Altix systems would perform with commercial workloads.
The performance demonstrated by Altix systems in computational areas are also a testament to the design of the system. More than anything, it goes to show the impact that a good system infrastructure can have on overall performance. Perhaps the greatest difference between the Altix and other Itanium 2 based systems is the available bandwidth within a single ‘cell’. Other systems have 4 processors per local cell, while the Altix has only 2, giving each processor twice the effective bandwidth. This architecture is showing its merits today, and once Montecito is released, these advantages will be accentuated by multithreading. Montecito’s multithreading will allow for greater parallelism and will require even more bandwidth than its predecessors. It will be quite exciting to examine the different Montecito based systems and see how the available bandwidth affects the overall performance.
 SGI Altix webpage – www.sgi.com/altix
 Whitepapers – www.sgi.com/whitepapers
 About NASA AMES and Altix – www.sgi.com/features/2003/nov/nasa
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