ABSTRACT
It was mentioned already in the section on ccNUMA architecture that, for applications whose performance is bound by memory bandwidth, locality and contention problems (see Figures 8.1 and 8.2) tend to turn up when threads/processes and their data are not carefully placed across the locality domains of a ccNUMA system. Unfortunately, the current OpenMP standard (3.0) does not refer to page placement at all and it is up to the programmer to use the tools that system builders provide. This chapter discusses the general, i.e., mostly system-independent options for correct data placement, and possible pitfalls that may prevent it. We will also show that page placement is not an issue that is restricted to shared-memory parallel programming.
8.1 Locality of access on ccNUMA Although ccNUMA architectures are ubiquitous today, the need for ccNUMA-
awareness has not yet arrived in all application areas; memory-bound code must be designed to employ proper page placement [O67]. The placement problem has two dimensions: First, one has to make sure that memory gets mapped into the locality domains of processors that actually access them. This minimizes NUMA traffic
