> > > > Note that MPI implementations may be interested in taking advantage of > > https://software.intel.com/en-us/blogs/2016/10/06/intel- > xeon-phi-product-family-x200-knl-user-mode-ring-3-monitor-and-mwait. > > Is that really useful if it's KNL-specific and MSR-based, with a setup > that implementations couldn't assume? > > Why wouldn't it be useful in the context of a parallel runtime system like MPI? MPI implementations take advantage of all sorts of stuff that needs to be queried with configuration, during compilation or at runtime.
TSX requires that one check the CPUID bits for it, and plenty of folks are happily using MSRs (e.g. http://www.brendangregg.com/blog/2014-09-15/the-msrs-of-ec2.html). > >> Is cpu_relax available to userland? (GCC has an x86-specific intrinsic > >> __builtin_ia32_pause in fairly recent versions, but it's not in RHEL6's > >> gcc-4.4.) > > > > The pause instruction is available in ring3. Just use that if cpu_relax > > wrapper is not implemented. > > [OK; I meant in a userland library.] > > Are there published measurements of the typical effects of spinning and > ameliorations on some sort of "representative" system? > > None that are published, unfortunately. Best, Jeff -- Jeff Hammond jeff.scie...@gmail.com http://jeffhammond.github.io/
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