Hammond, S.D., Mudalige, G.R., Smith, J.A., Davis, J.A., Jarvis, S.A., Holt, J., Miller, I., Herdman, J.A. and Vadgama, A. (2010) To Upgrade or not to Upgrade? Catamount vs. Cray Linux Environment. In: Large Scale Parallel Processing Workshop 2010 (LSPP10), Atlanta, Georgia, USA.
Abstract
Modern supercomputers are growing in diversity and complexity -- the arrival of
technologies such as multi-core processors, general purpose-GPUs and specialised
compute accelerators has
increased the potential scientific delivery possible from such machines. This is
not however without some cost, including significant increases in the
sophistication and complexity of supporting operating systems and software
libraries. This paper documents the development and application of methods to
assess the 
of selecting one hardware, operating
system (OS) and software stack combination against another. This is of
particular interest to supercomputing centres, which routinely examine
prospective software/architecture combinations and possible machine upgrades. A
case study is presented that assesses the potential performance of a particle
transport code on AWE's Cray XT3 8,000-core supercomputer running images of the
Catamount and the Cray Linux Environment (CLE) operating systems. This work
demonstrates that by running a number of small benchmarks on a test machine and
network, and observing factors such as operating system noise, it is possible to
speculate as to the performance impact of upgrading from one operating system to
another on the system as a whole. This use of performance modelling represents
an inexpensive method of examining the likely behaviour of a large supercomputer
before and after an operating system upgrade; this method is also attractive if
it is desirable to minimise system downtime while exploring software-system
upgrades. The results show that benchmark tests run on less that 256 cores would
suggest that the impact (overhead) of upgrading the operating system to CLE was
less than 10%; model projections suggest that this is not the case at scale.
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