Thanks for the articles and the response! Yes, it's a CPU state, but I'm pretty sure that by default different compilers set it differently at thread start (or

Thanks for the articles and the response! Yes, it's a CPU state, but I'm pretty sure that by default different compilers set it differently at thread start (or alternatively, choose to leave it as is). The ICC to GCC switch was the one that tricked me. So while the changes at runtime can override either, in the absence of an explicit override you'll often see different behavior based on compiler choice. Useful details and links here: http://stackoverflow.com/questions/9314534/why-does-changing-0-1f-to-0-slow-down-performance-by-10x http://stackoverflow.com/questions/9314534/why-does-changing...