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Comment by robabbott | Hacker News Reader

In addition to GPU, Cray has recently added the Intel Phi coprocessor to its XC30 Cascade supercomputers (http://investors.cray.com/phoenix.zhtml?c=98390&p=irol-newsA...). I think that this supports the argument that certain problems are better handled on traditional processors than on GPGPU platforms.

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The Xeon Phi resembles a GPU much more than it does a CPU. The original project, Larrabee, was at one point meant to be a GPU that competed with NVIDIA and ATI.

It's a multicore x86. It resembles GPUs only in the sense that it sits on its own PCIe board and has a lot of cores, but the programming model is just x86. It would have been very different from the NVidia/AMD competition if it had ended up as a GPU.

One of the biggest obstacles to GPGPU exploitation is being at the mercy of each vendors proprietary software stack and the resulting fragmentation & lack of openness. It's like the pre-PC era, without Unix... Larrabee might have helped. Now Xeon Phi is a niche product.

It is an x86 with very weak in-order cores, which instead have very large (512-bit) vector units. Very much like an NVIDIA "symmetric multiprocessor". If you try to program the Xeon Phi anything like a general-purpose CPU, you will not get within 5% of its power --- the programming model is essentially that of a GPU. The one thing that makes the Xeon Phi more general-purposy than current GPUs is the cache-coherence across cores.

They are programmed the way shared memory parallel machines have been used since time immemorial in the HPC world. Hundreds of cores is normal there. The same Intel software stack (OpenMP, Threaded Building Blocks, parallel Fortran etc) is used, same one that Intel markets for regular HPC.

Yeah, you have slower cores and the SIMD is twice as wide, but its main selling point is that you get to keep the regular programming model - unlike with NVidia or AMD. Along with benefits that come with it (mature software, openness, etc).

See eg. Intel's Xeon Phi Programmin Guide for an intro: http://software.intel.com/sites/default/files/article/330164...

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