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That's what some people were doing with SuperH; I don't know how the project has progressed. https://lwn.net/Articles/647636/ https://lwn.net/Articles/647636/
by bonzini 9y ago
That's what some people were doing with SuperH; I don't know how the project has progressed.
https://lwn.net/Articles/647636/ https://lwn.net/Articles/647636/
[If you wanted to resurrect the Alpha, though, please do not resurrect the crazy memory consistency semantics, where you need to put a full memory barrier between
r0 = load(&x);
r1 = load(r0);
- wbl 9y agoHow else will I be able to bank the lower-level cache for the absolute highest in performance?
- KMag 9y agoDo you have any pointers to good documentation on the Alpha memory semantics? The memory semantics are of course so lax so that the processor doesn't need to check the computed addresses of all in-flight stores before issuing a concurrent memory operation. My understanding is that it's mostly a footgun for assembly programmers, but I'd love to see any estimates of the speed and power efficiency benefits of the lax memory semantics.
- gsmadhusudan 9y agoThis is one of the raging debates within the RISC-V group and elsewhere. Is weak memory semantics really worth it or can x86 style TSO be implemented optimally.Lot of anecdotal evidence but no conclusive experiment. As part of our work we hope to try multiple memory models in our I-class and get some definitive answers.RISC-V by the way supports ARM/PPC style weak memory model or optionally an x86 style TSO.
- bonzini 9y agoARM/PPC is fine, but Alpha took it too far in my opinion (and also didn't have a read memory barrier instruction---nowadays acquire and release memory barriers would probably be preferrable).