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RISC-V: They Should Have Known Better

dmitry.gr

51–60 of 467 posts

Re: RISC-V: They Should Have Known Better

#51

> After being asked for the Nth time to explain, I decided to put it all down in one place so that I could simply link to it when asked next. Bookmarked, because I've needed the same. The worst part of all this is that they really should have known better by now. In 1980 you could make these kinds of mistakes, because this was pretty new territory. In 2020, doing this just makes you stupid. Or ignorant. Or both.

I’m not so sure - the 6502 existed in 1980 and showed the way.

6809 is a better exemplar, but, yeah, we knew this stuff way back when.

The problem is that everybody around RISC-V wants to sell IP instead of a chip. Most of the worst brain damage follows from that.

The rest of the brain damage follows from "We want to compete with ARM A-Series cores." No. Just ... no. Nobody willing to spend that much on a processor gives one iota of damn about ARM licensing fees.

So, the semiconductor market wants a cheap, consistent chip that operates in the deep embedded space while the RISC-V ecosystem considers the mere thought of that to be icky beyond reason. And China will push on this like Longsoon and pray that somebody figures out how to make it not suck (Prediction: they won't succeed.)

And, the worst part is that RISC-V has basically lost its window. The single possible advantage that RISC-V had was that as people converged to a shared tooling ecosystem it would create lockout. Unfortunately, that convergence never happened so, at best, we got some shared compilers. And, now, AIs can basically one shot all your other tools around it and probably the compiler not far behind. And there goes your ecosystem lockout.

Re: RISC-V: They Should Have Known Better

#52
post #13

I can definitely see his argument, although I still do believe RISC-V did a lot of things better than x86... I really do hope that the arch is eventually able to fix this. Better that there be an open ISA than them all be closed IMO.

He has good points, except he misses the goal posts completely.

Re: RISC-V: They Should Have Known Better

#53
post #9

It's basically MIPS all over again The conclusion is honest, and you can of course brute force any ISA into any role. I used to loathe x86 for that reason, but now that I'm older I respect the game.

X86 is the best argument that you can build a fast efficient RISC-V chip... because the X86 instruction set is a much bigger mess.

It just blows my mind sometimes when designers don't learn insanely obvious lessons from the past, basic stuff like "complexity is evil" and "make the fast path overlap with the most common use cases" and "a standard with N optional extensions is actually N! (N factorial) standards."

That being said all real world architectures seem to have messy corners and warts. RISC-V was a chance to do away with a lot of that and they... didn't?

Re: RISC-V: They Should Have Known Better

#54

RISC-V is... fine. It satisfies my two requirements for an ISA as a hobby CPU designer, which are: 1. Supported in mainline LLVM and GCC. 2. I can implement it without lawyers sending me a love letter. Everything else, I can fix in post. There are enough good ideas spread across the extensions that I can assemble a reasonably put-together, curated embedded ISA with competitive performance and code density that admits…

> RISC-V is... fine

Exactly.

> It satisfies my two requirements for an ISA as a hobby CPU designer...

You probably have some unstated requirements as well, such as available toolchains and "vetted well enough to actually be able to run code."

Risc-V now occupies the Schelling point for people who, for whatever reason (rent-seeking and security top the list) want to leave the x86 and Arm ecosystems.

Re: RISC-V: They Should Have Known Better

#55

Why is he complaining about everything being optional in RISC-V? Isn't that the whole idea of RISC-V? The market can sort it out for themselves. RISC-V is already dominant in the MCU space despite its flaws, and many of them will be solved in due time. Most MCUs are used for dead-simple solutions, like electric blankets and microwaves with segment displays or LEDs. Whether their interrupts are handled in 44 or 22 cyc…

>"RISC-V is already dominant in the MCU space[...]"

Where are you getting the idea that RISC-V is dominant? As someone who works in this space, that doesn't jive with my experience or the sources I've seen.[1] 32-bit microcontrollers only recently achieved a majority market share for gosh sakes!

RISC-V is claiming that they have achieved 25% market share across selected segments, but they're still behind ARM (and x86).[2]

[1] https://www.grandviewresearch.com/industry-analysis/microcon...

[2] https://www.aestechno.com/en/risc-v-2026-arm-x86-market/

Re: RISC-V: They Should Have Known Better

#56
post #49

the significance and allure of risc-v, the reason china is investing heavily in it right now, has little to do with the technical details of how it works under the hood, it's the fact that it is an open standard not encumbered by intellectual property law. even if it isn't technically the best general-purpose processor architecture, it sets an important precedent by proving that it is possible to develop an open publ…

> it's the fact that it is an open standard not encumbered by intellectual property law.

There are actually many of those. But Risc-V has become, through effective marketing, the Schelling point for anybody who wants to avoid the x86 and Arm ecosystems, both for the rent-seeking behaviors you mention, and also, in some instances, for security reasons.

And, as others have mentioned, the ISA doesn't really matter. As long as it's agreed upon, then the CPU vendors can optimize on one side, and the compiler writers on the other side.

Sure, Risc-V has its warts, but you can certainly say the same about all the rest.

Re: RISC-V: They Should Have Known Better

#57
post #51

Earlier quoted context omitted.

I’m not so sure - the 6502 existed in 1980 and showed the way.

6809 is a better exemplar, but, yeah, we knew this stuff way back when. The problem is that everybody around RISC-V wants to sell IP instead of a chip . Most of the worst brain damage follows from that. The rest of the brain damage follows from "We want to compete with ARM A-Series cores." No. Just ... no. Nobody willing to spend that much on a processor gives one iota of damn about ARM licensing fees. So, the semico…

Because selling "bits" is very lucrative, whilst actual hardware can lead to huge losses if it doesn't sell. Just ask Microsoft.

It's no wonder Microsoft is pulling out of the game console market and handing it over to PC manufacturers to make the actual hardware.

Re: RISC-V: They Should Have Known Better

#58
post #54

RISC-V is... fine. It satisfies my two requirements for an ISA as a hobby CPU designer, which are: 1. Supported in mainline LLVM and GCC. 2. I can implement it without lawyers sending me a love letter. Everything else, I can fix in post. There are enough good ideas spread across the extensions that I can assemble a reasonably put-together, curated embedded ISA with competitive performance and code density that admits…

> RISC-V is... fine Exactly. > It satisfies my two requirements for an ISA as a hobby CPU designer... You probably have some unstated requirements as well, such as available toolchains and "vetted well enough to actually be able to run code." Risc-V now occupies the Schelling point for people who, for whatever reason (rent-seeking and security top the list) want to leave the x86 and Arm ecosystems.

They did explicitly specify:

> 1. Supported in mainline LLVM and GCC.

Which pretty well encapsulates the ecosystem requirements.

Re: RISC-V: They Should Have Known Better

#59
post #33

Earlier quoted context omitted.

I don't think I've read a more "doesn't actually know anything about how software is produced, but with absolute confidence knows everything about it" post in a very long time.

So you write software for a platform you know nothing about?

Very often. Yes. Or software that will run on any similar arch by auto detecting the environment.

Re: RISC-V: They Should Have Known Better

#60
post #55

Why is he complaining about everything being optional in RISC-V? Isn't that the whole idea of RISC-V? The market can sort it out for themselves. RISC-V is already dominant in the MCU space despite its flaws, and many of them will be solved in due time. Most MCUs are used for dead-simple solutions, like electric blankets and microwaves with segment displays or LEDs. Whether their interrupts are handled in 44 or 22 cyc…

> "RISC-V is already dominant in the MCU space[...]" Where are you getting the idea that RISC-V is dominant? As someone who works in this space, that doesn't jive with my experience or the sources I've seen.[1] 32-bit microcontrollers only recently achieved a majority market share for gosh sakes! RISC-V is claiming that they have achieved 25% market share across selected segments, but they're still behind ARM (and x8…

Risc-v is nowhere near dominant, people are just being swayed by headlines such as Western Digital or Nvidia shipping billions of risc-v cores.

I do find it odd that you go on and compare to x86 marketshare however, the topic you've quoted is very clearly about MCU and whilst 8086 MCU still exists they haven't been used in greenfield projects for decades. Let alone any more recent x86 implementation.

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