4 ms·

I like the idea of RISC-V, applaud the designers and wish it well, but there is a lot of slightly purple prose here about the benefits of an open and 'free' ISA

I like the idea of RISC-V, applaud the designers and wish it well, but there is a lot of slightly purple prose here about the benefits of an open and 'free' ISA. I can see how RISC-V works for SoC designers who either 1. Want to cut costs to a minimum or 2. Want to add their own proprietary extensions to distinguish it from the competition. I'm less sure that it works for everyone else. The instruction set running on your Raspberry PI is the same as that running on your iPhone which in turn is the same as that running on an Ampere Server. Do we really want to be faced with a multiplicity of distinct ISAs?

melling 6y ago
More competition means more innovation and lower prices. The compiler abstracts the instruction set for most people.
- klelatti 6y ago
  I'm old enough to remember when there was a lot of ISA competition. Trouble was each ISA had no longevity, you were dependent on one vendor typically and choosing an ISA was pot luck. I don't think it's reasonable to expect compiler writers to solve any fragmentation issues. As I said I like RISC-V and think it's laudable. We just need to recognise the downsides and not get too carried away.
  - d_tr 6y ago
    It is definitely a must to try and find downsides and weigh them, but even with RISC-V thrown into the mix, the situation will be far from what it was 25 - 35 years ago, and in addition the tools are much more advanced. Modern compilers can already deal with several permutations of ISA extensions. Of course, there are limits to everything, so having everyone and his grandma creating his own extension will be messy / ugly...
    - klelatti 6y ago
      Very much agree!
d_tr 6y ago
> Do we really want to be faced with a multiplicity of distinct ISAs? There exist excellent and free / open-source tools for dealing with this kind of inconvenience. Even then, is it worth it? IMO, yes, because screw having to pay and get blessings for the legal right to merely execute an instruction stream on a processor of your own design. However, the possible fragmentation issues are a concern, but mainly within the RISC-V ISA itself with all the extensions that will probably start popping up.
- klelatti 6y ago
  I worry about a 'tragedy of the commons' type situation emerging here. RISC-V isn't 'GPL' in any meaningful sense so the danger is that we effectively see a series of 'forks' by the most powerful SoC designers - they add their own instructions etc and use their designs to crowd others out. What if Apple and Samsung together forked ARMv8 added its own instructions and everyone started writing their code for that variant because of their market power? I understand why ARM isn't necessarily the most popular firm and why the fees / control aren't ideal but I do think its important to think through the full implications of any market change like this.
  - megameter 6y ago
    It is sometimes said of the 21st century that it is an era of customization. If we take that notion as the gospel truth, there is no part of the computing stack that can survive as a stable, uniform standard, including the base architecture. But computing as a whole is resilient to such changes. Having a special hardware instruction is a competitive advantage if it's used, but it tends to exist as implementation detail and doesn't carry the weight of an end-user feature. A chip design can target some subset of applications, but software fallbacks are expected, and software developers increasingly don't attempt to optimize to the hardware, making it a commodity. In that light RISC-V arrives at a time where it's very unlikely to matter. A decreasing share of applications will need to look that deeply.
nix23 6y ago
>Do we really want to be faced with a multiplicity of distinct ISAs? Yes! My computer already have lots of them (GPU, Network-card, SSD-Controler, Intel-ME (ok bad example) and so on)
- klelatti 6y ago
  Do you have to maintain codebases for your network card and SSD Controller?
  - nix23 6y ago
    Would be nice to have the firmware opensource. Do YOU have to maintain the codebase of your operating-system? If you want to know howto maintain Code for multiple ISA's ask netbsd and openbsd.
    - klelatti 6y ago
      No but I do have a codebase to maintain and the more architectures the more work! My underlying point was that there are trade offs - more architectures - great for some but a lot more work for others. I'm sure the BSD's go a great job supporting lots of architectures - but they represent a small part of the overall software ecosystem.
      - nix23 6y ago
        > BSD's go a great job supporting lots of architectures Well its an OS, and by the definition the Software that has the most dependencies ISA wise, and it's kind of 'easy' to bring it to another architecture. >No but I do have a codebase to maintain and the more architectures the more work! Depends on your Software and your Language...sure can be more work, but supporting multiple OS's, Databases, Filesystems too.
nickik 6y ago
> Do we really want to be faced with a multiplicity of distinct ISAs? Yes. We want distinct ISA where it makes sense for the application. You want to have little sensor controller, should it really be the same as a gigantic parallel server? RISC-V deals with this by creating 'profiles' meaning specific configurations that apply to applications of a particular field. And of course the tools of RISC-V should be designed to handle these situations.
ksec 6y ago
It kind of "depends". People are talking about cost of licensing, but the cost of ARM are peanuts compared to cost of design and fabrication. I am not even sure if the word peanuts correctly describes it. ARM has made changes that you no longer need some one-off fees before you start producing "certain" ARM design. You get access to it and only paid for it once you start making revenue. RISC-V makes sense for tiny microcontroller that ships in tens of millions. Western Digital saves millions every year just by switching to RISC-V for Microcontroller used in their HDD. RISC-V's main competition is the like of ARC and some other DSP. It is competing with ARM in certain segment ( or the old ARM embedded segment ). But it is not competing ARMv8.
- klelatti 6y ago
  Agree 100%. No argument that RISC-V is both interesting and has a lot of value. Just not that enthused by the "a new golden age" and "will eventually supplant x86 and ARM" commentary being presented (primarily) on the basis of ISA customisation without a broader discussion of the pros and cons and wider market issues.

melling 6y ago

More competition means more innovation and lower prices. The compiler abstracts the instruction set for most people.

klelatti 6y ago
I'm old enough to remember when there was a lot of ISA competition. Trouble was each ISA had no longevity, you were dependent on one vendor typically and choosing an ISA was pot luck. I don't think it's reasonable to expect compiler writers to solve any fragmentation issues. As I said I like RISC-V and think it's laudable. We just need to recognise the downsides and not get too carried away.
- d_tr 6y ago
  It is definitely a must to try and find downsides and weigh them, but even with RISC-V thrown into the mix, the situation will be far from what it was 25 - 35 years ago, and in addition the tools are much more advanced. Modern compilers can already deal with several permutations of ISA extensions. Of course, there are limits to everything, so having everyone and his grandma creating his own extension will be messy / ugly...
  - klelatti 6y ago
    Very much agree!

d_tr 6y ago

> Do we really want to be faced with a multiplicity of distinct ISAs? There exist excellent and free / open-source tools for dealing with this kind of inconvenience. Even then, is it worth it? IMO, yes, because screw having to pay and get blessings for the legal right to merely execute an instruction stream on a processor of your own design. However, the possible fragmentation issues are a concern, but mainly within the RISC-V ISA itself with all the extensions that will probably start popping up.

klelatti 6y ago
I worry about a 'tragedy of the commons' type situation emerging here. RISC-V isn't 'GPL' in any meaningful sense so the danger is that we effectively see a series of 'forks' by the most powerful SoC designers - they add their own instructions etc and use their designs to crowd others out. What if Apple and Samsung together forked ARMv8 added its own instructions and everyone started writing their code for that variant because of their market power? I understand why ARM isn't necessarily the most popular firm and why the fees / control aren't ideal but I do think its important to think through the full implications of any market change like this.
- megameter 6y ago
  It is sometimes said of the 21st century that it is an era of customization. If we take that notion as the gospel truth, there is no part of the computing stack that can survive as a stable, uniform standard, including the base architecture. But computing as a whole is resilient to such changes. Having a special hardware instruction is a competitive advantage if it's used, but it tends to exist as implementation detail and doesn't carry the weight of an end-user feature. A chip design can target some subset of applications, but software fallbacks are expected, and software developers increasingly don't attempt to optimize to the hardware, making it a commodity. In that light RISC-V arrives at a time where it's very unlikely to matter. A decreasing share of applications will need to look that deeply.

nix23 6y ago

>Do we really want to be faced with a multiplicity of distinct ISAs? Yes! My computer already have lots of them (GPU, Network-card, SSD-Controler, Intel-ME (ok bad example) and so on)

klelatti 6y ago
Do you have to maintain codebases for your network card and SSD Controller?
- nix23 6y ago
  Would be nice to have the firmware opensource. Do YOU have to maintain the codebase of your operating-system? If you want to know howto maintain Code for multiple ISA's ask netbsd and openbsd.
  - klelatti 6y ago
    No but I do have a codebase to maintain and the more architectures the more work! My underlying point was that there are trade offs - more architectures - great for some but a lot more work for others. I'm sure the BSD's go a great job supporting lots of architectures - but they represent a small part of the overall software ecosystem.
    - nix23 6y ago
      > BSD's go a great job supporting lots of architectures Well its an OS, and by the definition the Software that has the most dependencies ISA wise, and it's kind of 'easy' to bring it to another architecture. >No but I do have a codebase to maintain and the more architectures the more work! Depends on your Software and your Language...sure can be more work, but supporting multiple OS's, Databases, Filesystems too.

nickik 6y ago

> Do we really want to be faced with a multiplicity of distinct ISAs? Yes. We want distinct ISA where it makes sense for the application. You want to have little sensor controller, should it really be the same as a gigantic parallel server? RISC-V deals with this by creating 'profiles' meaning specific configurations that apply to applications of a particular field. And of course the tools of RISC-V should be designed to handle these situations.

ksec 6y ago

It kind of "depends". People are talking about cost of licensing, but the cost of ARM are peanuts compared to cost of design and fabrication. I am not even sure if the word peanuts correctly describes it. ARM has made changes that you no longer need some one-off fees before you start producing "certain" ARM design. You get access to it and only paid for it once you start making revenue. RISC-V makes sense for tiny microcontroller that ships in tens of millions. Western Digital saves millions every year just by switching to RISC-V for Microcontroller used in their HDD. RISC-V's main competition is the like of ARC and some other DSP. It is competing with ARM in certain segment ( or the old ARM embedded segment ). But it is not competing ARMv8.

klelatti 6y ago
Agree 100%. No argument that RISC-V is both interesting and has a lot of value. Just not that enthused by the "a new golden age" and "will eventually supplant x86 and ARM" commentary being presented (primarily) on the basis of ISA customisation without a broader discussion of the pros and cons and wider market issues.