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Main lesson: we failed to make all the software JIT-compiled or AOT-recompiled-on-boot or something, that would allow retargeting the optimizations for the new

Main lesson: we failed to make all the software JIT-compiled or AOT-recompiled-on-boot or something, that would allow retargeting the optimizations for the new generation of a VLIW CPU. Barely anyone even tried. Well I guess in the early 2000s there was this vision that everything would be Java, which is JIT, but lol

dragontamer 6y ago
Your point seems invalid, in the face of a large chunk of HPC (neural nets, matrix multiplication, etc. etc.) getting rewritten to support CUDA, which didn't even exist back when Itanium was announced. VLIW is a compromise product: its more parallel than a traditional CPU, but less parallel than SIMD/GPUs. And modern CPUs have incredibly powerful SIMD engines: AVX2 and AVX512 are extremely fast and parallel. There are compilers that auto-vectorize code, as well as dedicated languages (such as ipsc) which work for SIMD. Encoders, decoders, raytracers, and more have been rewritten for Intel AVX2 SIMD instructions, and then re-rewritten for GPUs. The will to find faster execution has always existed, but unfortunately, Itanium failed to perform as well as its competition.
- floatboth 6y ago
  I'm not talking about rewrites and GPUs. I'm saying we do not have dynamic recompilation of everything. As in – if we would have ALL binaries that run on the machine (starting with the kernel) stored in some portable representation like wasm (or not-fully-portable-but-still-reoptimizable like llvm bitcode) and recompiled with optimization for the current exact processor when starting. Only that would solve the "new generation of VLIW-CPU needs very different compiler optimizations to perform, oops all your binaries are for first generation and they are slow now" problem. GPUs do work like this – shaders recompiled all the time – so VLIW was used in GPUs (e.g. TeraScale). But on CPUs we have a world of optimized, "done" binaries.

dragontamer 6y ago

Your point seems invalid, in the face of a large chunk of HPC (neural nets, matrix multiplication, etc. etc.) getting rewritten to support CUDA, which didn't even exist back when Itanium was announced. VLIW is a compromise product: its more parallel than a traditional CPU, but less parallel than SIMD/GPUs. And modern CPUs have incredibly powerful SIMD engines: AVX2 and AVX512 are extremely fast and parallel. There are compilers that auto-vectorize code, as well as dedicated languages (such as ipsc) which work for SIMD. Encoders, decoders, raytracers, and more have been rewritten for Intel AVX2 SIMD instructions, and then re-rewritten for GPUs. The will to find faster execution has always existed, but unfortunately, Itanium failed to perform as well as its competition.

floatboth 6y ago
I'm not talking about rewrites and GPUs. I'm saying we do not have dynamic recompilation of everything. As in – if we would have ALL binaries that run on the machine (starting with the kernel) stored in some portable representation like wasm (or not-fully-portable-but-still-reoptimizable like llvm bitcode) and recompiled with optimization for the current exact processor when starting. Only that would solve the "new generation of VLIW-CPU needs very different compiler optimizations to perform, oops all your binaries are for first generation and they are slow now" problem. GPUs do work like this – shaders recompiled all the time – so VLIW was used in GPUs (e.g. TeraScale). But on CPUs we have a world of optimized, "done" binaries.