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Why support real hardware? Old as Alpha AXP CPUs are they are still orders of magnitude faster than emulating the instruction set. Why care about the instructi
by crest 5y ago
Why support real hardware? Old as Alpha AXP CPUs are they are still orders of magnitude faster than emulating the instruction set.
Why care about the instruction set? It a very good regression test for the kernel locking primitives and data structures. Something "boring" like x86 with its TSO memory model will hide bugs.
- zamadatix 5y agoIs there something special about Alpha that makes it hundreds of times harder to emulate? X86 Windows XP on my M1 MacBook runs CPU bound workloads faster than my XP machine in 2004 did and that's not even using the extra X86 emulation specific parts of the M1 cores, just bog standard QEMU.
- skissane 5y agoProbably because a lot of effort goes into optimising x86 emulation to be as efficient as possible, whereas I doubt anyone is motivated to make the same investment in DEC Alpha emulation. In practice that will make Alpha emulation slower than x86, quite apart from any technical features of their respective architectures which may impact the efficiency of emulation.
- retrac 5y agoRight. There's no fundamental impediment to writing a super fancy JIT translator from Alpha to another architecture. Such a thing actually exists as part of VMS! DEC was one of the first to use binary translation commercially like that. First to run VAX code on Alpha, and then Alpha code on Itanium. And now Alpha and VAX code on x86. (Doesn't look like VSI will bother with Itanium to x86 on the assumption customers will have source.)
- __d 5y agoIs it _really_ a bug if it functions correctly on supported hardware?