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I'm really surprised by those two lines blog posts that gloss over the complexity of ISA design and ecosystem and concludes riscv creator know nothing about not

by guerby 6y ago

I'm really surprised by those two lines blog posts that gloss over the complexity of ISA design and ecosystem and concludes riscv creator know nothing about nothing. May be I'm biased because I learned computer architecture at my university reading Computer Architecture a Quantitative Approach (in 1995, yes I'm old). This a long and very detailed book with lots and lots of data about tradeoffs in ISA design. The authors of this book created MIPS and then RISC-V so it's not just academia-only data. I would love to hear about people who really have done their homework and say with this different RISC-V design over a few thousands tests of various linux/bsd tools/software we gain X% on Y metric. With an open source simulator and tooling provided to verify the claim. But I think it's mostly talk is cheap (and cheap money from competitor interest ...). End of rant.

wmf 6y ago
Plenty of people consider ARMv8 a better ISA than RISC-V; the addressing modes seem to be a real concern. Those same people mostly consider MIPS to be too simple for its own good; obviously this simplicity doesn't completely doom the architecture but there are some long-standing differences of opinion here.
- brucehoult 6y ago
  There is plenty of evidence (rather than opinion) that with a decent compiler and hardware implementation the more complex addressing modes don't gain you anything worth the bother in either code size or performance. RISC-V is extensible. If someone really believes that more complex addressing modes are worth it then they can add them as a custom extension. If their chips work out to have better performance/price, performance/area, performance/energy then everyone else will want to copy them and those more complex addressing modes will become a standard extension for RISC-V. There is no sign of the RISC-V community (as opposed to ARM or x86 fans who aren't using RISC-V anyway) moving in that direction.

by guerby 6y ago

wmf 6y ago

Plenty of people consider ARMv8 a better ISA than RISC-V; the addressing modes seem to be a real concern. Those same people mostly consider MIPS to be too simple for its own good; obviously this simplicity doesn't completely doom the architecture but there are some long-standing differences of opinion here.

brucehoult 6y ago
There is plenty of evidence (rather than opinion) that with a decent compiler and hardware implementation the more complex addressing modes don't gain you anything worth the bother in either code size or performance. RISC-V is extensible. If someone really believes that more complex addressing modes are worth it then they can add them as a custom extension. If their chips work out to have better performance/price, performance/area, performance/energy then everyone else will want to copy them and those more complex addressing modes will become a standard extension for RISC-V. There is no sign of the RISC-V community (as opposed to ARM or x86 fans who aren't using RISC-V anyway) moving in that direction.