When we hear the term “multiprocessing,” we often associate it with “symmetric multiprocessing (SMP).” This is because of SMP’s initial prevalence in the high-performance computing world, and now in x86/x64 servers and PCs. However, it’s been known for years that SMP’s ability to scale performance as the number of cores increases is poor. (For more information on SMP’s inability to scale well, read Jack Ganssle’s 2008 embedded.com article, “The Nulticore Effect,” or the IEEE Spectrum/Sandia Labs article, “Multicore is Bad News for Supercomputers: Adding cores slows data-intensive applications.”)
see more on this Article by Kurt Shuler VP of Marking at Arteris a member of the HSA Foundation  at http://chipdesignmag.com/sld/shuler/2012/09/27/smp-asymmetric-multiprocessing-and-the-hsa-foundation/