5 ms·

Interesting. So I've seen a lot of reviews of RISC-V machines and they seem to be a decade or more behind in terms of performance. I always thought that was a

by andai 2mo ago

Interesting. So I've seen a lot of reviews of RISC-V machines and they seem to be a decade or more behind in terms of performance. I always thought that was a case of "the tech is still catching up",[0] but it sounds like there are fundamental issues that prevent performant implementations? If so... I heard China was investing heavily in RISC-V, which implies that either they're going to have to settle for permanently crippled perf, or find a way around the issues. -- [0] Making chips is an extremely high tech process with decades of trial and error and proprietary secrets, so this would be the logical explanation to me regardless of architecture. But I'm not hardware guy, so I'd love to hear more about this!

phire 2mo ago
No. Intel and AMD have proven that if you throw enough money at the problem, you can make fast microarchitectures despite a flawed ISA, and in many ways RISC-V is less flawed than x86. The things we are debating here are more along the lines of minor nitpicks. The main roadblock to the existence of fast RISC-V cores is the entrenchment of large x86 and arm ecosystems.
- simcop2387 2mo ago
  > The main roadblock to the existence of fast RISC-V cores is the entrenchment of large x86 and arm ecosystems. I'd disagree with that, their existence and decades of a head start mean they've been much more well invested but that's one of the things we're starting to see change, even if it's because of what would appear to be political motivations. We're starting to see a lot of investment into it in China because it looks like it's a reasonable way for tech sovereignty against the x86 monopoly. They've got licenses to some older (not sure about newer) AMD processor designs, I think around Zen2 architecture, for one of their major manufacturing firms but that won't easily let them move forward since they've got to do a lot of work to keep it up with compatibility and performance for newer ISA additions and such. That's one of the reasons they've been subsiding development of LoongSong64 and RISC-V to the point where for a while the larger LoongSong64 cores were illegal to export to some countries[0]. And then you've got a lot of other companies building faster RISC-V cores, for yes more embedded style designs but not the usual traditional embedded designs either. You've got TensTorrent working on AI work loads with real hardware out there that at least for ML stuff can compete on inference if you can get your software to run on it, and then you've got Bolt doing similar for GPU workloads[1]. While both of those are closer to embedded since you're not going to use them as a desktop, they're still making really fast RISC-V cores that could be theoretically turned into a standard RVA23 core by adding the missing extensions to make it work. That's of course not trivial but the entrenchment of x86 and arm aren't quite as daunting as they might have originally seemed. It's still not as fast as I'd like, simply because I want to start seeing some RISC-V mini pcs get made that are fine for a daily driver office pc to happen. [0] https://www.tomshardware.com/news/china-bans-exports-of-its-loongson-cpus-to-russia-other-countries https://www.tomshardware.com/news/china-bans-exports-of-its-... [1] https://bolt.graphics/ https://bolt.graphics/
  - phire 2mo ago
    You aren't disagreeing with the existence of the roadblock, just how hard it is to overcome. And yes, there is a bunch of funding being pumped into it. I do have hope that some kind of RISC-V linux workstation will be viable in the next 5 years, without sacrificing too much performance or my wallet. I just wouldn't expect that to translate into making inroads into existing markets where x86 and arm have moats, like android/apple smartphones and more typical desktop/laptop workloads (even on linux). I wouldn't count the AI/GPU stuff, those are generally pretty simple RISC pipelines with large vector units. Though TensTorrent do actually have a high-performance out-of-order rva23 core [1] that would be able to compete in this space. They are currently selling it as a "core for agentic workloads" [1] https://tenstorrent.com/en/ip/risc-v-cpu9719654910d.pdf https://tenstorrent.com/en/ip/risc-v-cpu9719654910d.pdf
    - sharpshadow 2mo ago
      The XuanTie C950 looks pretty beefy for a RISC-V chip with integrated TPE. But it isn’t available commercially. They are moving fast in China, wouldn’t be surprised if they offer a breaking integrated solution in the near future. There aren’t any benchmarks available for the C950 but the comparisons go towards early Apple M-Series performance.
- nicman23 2mo ago
  the x86 is just an abstraction layer at this point
acutelittlebox 2mo ago
the current highest performance RISC-V systems you can buy off a shelf are equivalent to a raspberry pi 5 so they're not terribly behind. in terms of IPC, currently available RISC-V cores are already basically on par with Zen 3 and Apple M1 from what i understand and Jim Keller believes that RISC-V will be the one that leads the way for raw performance.
- LeFantome 2mo ago
  SiFive P870 and Tenstorrent Ascalon are pretty much Zen 3. Tenstorrent is supposed to be releasing silicon soon. You can license their cores now. SiFive says customers have the P870 already but I am not sure who those are.
  - sylware 2mo ago
    Are they on the latest silicon process? Because, without neglecting the micro-architecture, we all know how critical the silicon process is for high-end performance.
    - LeFantome 2mo ago
      The first Ascalon silicon, Atlantis, will not be the latest process. As you say, that will impact performance. But there are plans for other chips to use newer process, and of course you can license and do what you like. The point is that RISC-V is not limited to lower performance by the ISA.
      - sylware 2mo ago
        So RISC-V is 'dragged down' because it cannot access the best silicon process (hardware big tech is hogging production capacity... how convenient...)
  - camel-cdr 2mo ago
    I think it will be closer to Zen 1/2
  - 2mo ago
mosura 2mo ago
> it sounds like there are fundamental issues that prevent performant implementations? This has always been true, it is just this is one of those projects that gets some people very emotionally invested so such discussions do not happen in public. See also Android, rust, webassembly, webgpu and so on.
muyuu 2mo ago
the main problem with RISC-V is also the main selling point: there is no single owner company behind steering development and making sweeping decisions how will that pan out over the long term is really unclear and the reality is performance is actually catching up quickly
- LeFantome 2mo ago
  History tells us that open standards pretty much always beat out proprietary ones in the end. You cannot buy the company backing RISC-V to take out the competition. And if a RISC-V company stumbles, the ecosystem carries on. But if even one RISC-V company is in the right place at the right time, RISC-V can surge ahead. It is hard to imagine it does not dominate eventually.
  - genxy 2mo ago
    Which is really the subtext to Grinberg's rant. It has technical flaws that he dislikes, but those won't stop RISC-V from dominating in the market. You get these kinds of responses when something is too close to perfection. It suddenly gets judged in a much different light.
  - windward 2mo ago
    I don't agree with history telling us that at all. HDMI, MP3, MPEG, .docx, DirectX, CUDA, I'm sure there are more. History tells us that money wins. But I also think this is an example of a slight disingenuity in RISC-V being referred to as open-source. It's borrowing the clout of open-source software projects where the end user has the freedom to compile them at home. I can't fabricate a CPU at home, I'm still beholden to whatever patents the manufacturer chooses to license. SiFive have a >billion dollar valuation, for a business based on selling licences.
    - vachina 2mo ago
      Those standards are adopted because they work. And they work because someone poured in tons of RnD to make them work. And those people are incentivised to do the RnD because they get paid (patents). Nowadays nobody will want to work on foundational open source work for free only to enrich everyone else that builds on top of it.
madushan1000 2mo ago
x86 is a horrible architecture, but most of the modern high performance processors are x86. They're only now getting around to making comparatively performant ARM chips. Not having decently performing risc-v chips right now doesn't mean anything other than nobody spent enough time and money on accomplishing that.
dmitrygr 2mo ago
With enough effort, you can make a brick fly. X86 proves this. But if you are designing a new flying device, despite the fact that you could make a brick fly, you probably don’t want to design a brick. Why make it harder on yourself? Riscv took all this information in, and designed a very, very good brick.
- ant6n 2mo ago
  Wait, so RiscV is still also a brick, like x86?
  - dmitrygr 2mo ago
    in my opinion, yes. Given that it was a clean-sheet design with no legacy to support, and that it was done so recently as to have easily had the benefit of all the lessons of x86, mips, arm, sparc, powerpc, etc, yes, it left a lot of obvious improvements on the table.
- crote 2mo ago
  When everyone is trying to make bricks fly, having the most aerodynamic brick probably isn't a bad thing.
LeFantome 2mo ago
> China was investing heavily in RISC-V, which implies that either they're going to have to settle for permanently crippled perf Not quite. RISC-V application class processors are a new development. They are starting from behind but they are improving faster than the competition. The SpacemiT K3 is 4 times faster than the K1 for example. The Alibaba C950 will be about Apple M1 level performance. And even faster designs are already in the works. RISC-V is not “permenantly crippled”. It will catch up and maybe surpass ARM. It is more an economy of scale issue than anything.
- hylaride 2mo ago
  My understanding is that RISC-V needs both economies of scale AND chips that are manufactured at the bleeding edge fabs (smallest dies, etc) which is a lot more expensive. It's a chicken and egg problem as there's not (yet?) demand. The architectural limitations will remain until there's incentive to work on it. In many ways it's not much different than Linux was in the 1990s. It was cheap and useful, but often not as performant as commercial OSes (UNIX or even windows) until big corporate money came in and started piling resources into it. Distribution fragmentation was also an issue, which could still cause headaches for RISC-V (especially if some companies start adding proprietary performance extensions that others can't). So I think it remains to be seen how RISC-V will pan out (eg will the cloud vendors see enough of an ROI supporting it for higher end computing than buying ARM licences).
  - RetroTechie 2mo ago
    > RISC-V needs both economies of scale AND chips that are manufactured at the bleeding edge fabs (smallest dies, etc) which is a lot more expensive. It's a chicken and egg problem as there's not (yet?) demand Whatever leading-edge fab capacity (mostly TSMC) was available, is now tied up to supply the ongoing AI boom. And will remain so for the foreseeable future. Even if you'd have a RISC-V product for which demand/economics work out, chances are those fabs' order books are filled. Also: design is done in many places, but actual fabrication of RISC-V SoCs in largely centered in China. Which (afaik) doesn't lack IC fabrication capacity. But does lag in leading-edge fab capacity. So: off to older nodes. Which may hurt perf/W, cost effectiveness or transistor budget. Or pay a premium (pricing products out of markets), limited production, or long lead times. Of course this affects ARM based & other products too. But they've been in the optimization / mass fabrication / distribution pipeline much longer than most RISC-V based products. Catching up takes time, and top-tier fab capacity being swiped by Nvidia & co doesn't help to shorten that process. I don't think it's a demand problem. Consumers don't care what powers their phone/tablet/laptop as long as it does its job. So in principle the market is there (yeah.. I understand issues like Google still working on Android-RISC-V, Windows users probably wanting x86 for legacy software etc).
imtringued 2mo ago
So far the vast majority of complaints have been nothing burgers. The biggest valid complaint is the lack of dedicated mask registers for vector processing, that's a huge design flaw in the vector instructions since it makes register renaming and shadow registers mandatory. In other words, the problem here is that they didn't stick with the RISC philosophy of making everything explicit. Compressed instructions are mostly wasted encoding space, but from a performance perspective they don't matter. If they are slow then compilers will treat them as slow legacy instructions and stop using them or they will only emit aligned compressed instructions.
bsder 2mo ago
> I always thought that was a case of "the tech is still catching up",[0] but it sounds like there are fundamental issues that prevent performant implementations? Yes, the fundamental problem is the fact that everybody involved in RISC-V wants to sell IP instead of a chip. The problem with the RISC-V chips in non-embedded contexts (ie desktop or server) has absolutely nothing to do with the instruction set architecture (not entirely true but a really good first approximation). The problem is that performance is strongly dependent upon your high speed interfaces--memory, graphics, PCI, etc. And those blocks need to be strongly integrated in with your CPU interfaces. However, if you buy a whole bunch of IP blocks and then just wire them together, your performance is going to be sub-par. And this is what every single RISC-V chip that I know of currently is. It's not beyond someone to sit down and do the required integration like Apple did for ARM. There's just insufficient money in it so nobody is going to expend the engineers.

by andai 2mo ago

phire 2mo ago

No. Intel and AMD have proven that if you throw enough money at the problem, you can make fast microarchitectures despite a flawed ISA, and in many ways RISC-V is less flawed than x86. The things we are debating here are more along the lines of minor nitpicks. The main roadblock to the existence of fast RISC-V cores is the entrenchment of large x86 and arm ecosystems.

simcop2387 2mo ago
> The main roadblock to the existence of fast RISC-V cores is the entrenchment of large x86 and arm ecosystems. I'd disagree with that, their existence and decades of a head start mean they've been much more well invested but that's one of the things we're starting to see change, even if it's because of what would appear to be political motivations. We're starting to see a lot of investment into it in China because it looks like it's a reasonable way for tech sovereignty against the x86 monopoly. They've got licenses to some older (not sure about newer) AMD processor designs, I think around Zen2 architecture, for one of their major manufacturing firms but that won't easily let them move forward since they've got to do a lot of work to keep it up with compatibility and performance for newer ISA additions and such. That's one of the reasons they've been subsiding development of LoongSong64 and RISC-V to the point where for a while the larger LoongSong64 cores were illegal to export to some countries[0]. And then you've got a lot of other companies building faster RISC-V cores, for yes more embedded style designs but not the usual traditional embedded designs either. You've got TensTorrent working on AI work loads with real hardware out there that at least for ML stuff can compete on inference if you can get your software to run on it, and then you've got Bolt doing similar for GPU workloads[1]. While both of those are closer to embedded since you're not going to use them as a desktop, they're still making really fast RISC-V cores that could be theoretically turned into a standard RVA23 core by adding the missing extensions to make it work. That's of course not trivial but the entrenchment of x86 and arm aren't quite as daunting as they might have originally seemed. It's still not as fast as I'd like, simply because I want to start seeing some RISC-V mini pcs get made that are fine for a daily driver office pc to happen. [0] https://www.tomshardware.com/news/china-bans-exports-of-its-loongson-cpus-to-russia-other-countries https://www.tomshardware.com/news/china-bans-exports-of-its-... [1] https://bolt.graphics/ https://bolt.graphics/
- phire 2mo ago
  You aren't disagreeing with the existence of the roadblock, just how hard it is to overcome. And yes, there is a bunch of funding being pumped into it. I do have hope that some kind of RISC-V linux workstation will be viable in the next 5 years, without sacrificing too much performance or my wallet. I just wouldn't expect that to translate into making inroads into existing markets where x86 and arm have moats, like android/apple smartphones and more typical desktop/laptop workloads (even on linux). I wouldn't count the AI/GPU stuff, those are generally pretty simple RISC pipelines with large vector units. Though TensTorrent do actually have a high-performance out-of-order rva23 core [1] that would be able to compete in this space. They are currently selling it as a "core for agentic workloads" [1] https://tenstorrent.com/en/ip/risc-v-cpu9719654910d.pdf https://tenstorrent.com/en/ip/risc-v-cpu9719654910d.pdf
  - sharpshadow 2mo ago
    The XuanTie C950 looks pretty beefy for a RISC-V chip with integrated TPE. But it isn’t available commercially. They are moving fast in China, wouldn’t be surprised if they offer a breaking integrated solution in the near future. There aren’t any benchmarks available for the C950 but the comparisons go towards early Apple M-Series performance.
nicman23 2mo ago
the x86 is just an abstraction layer at this point

acutelittlebox 2mo ago

the current highest performance RISC-V systems you can buy off a shelf are equivalent to a raspberry pi 5 so they're not terribly behind. in terms of IPC, currently available RISC-V cores are already basically on par with Zen 3 and Apple M1 from what i understand and Jim Keller believes that RISC-V will be the one that leads the way for raw performance.

LeFantome 2mo ago
SiFive P870 and Tenstorrent Ascalon are pretty much Zen 3. Tenstorrent is supposed to be releasing silicon soon. You can license their cores now. SiFive says customers have the P870 already but I am not sure who those are.
- sylware 2mo ago
  Are they on the latest silicon process? Because, without neglecting the micro-architecture, we all know how critical the silicon process is for high-end performance.
  - LeFantome 2mo ago
    The first Ascalon silicon, Atlantis, will not be the latest process. As you say, that will impact performance. But there are plans for other chips to use newer process, and of course you can license and do what you like. The point is that RISC-V is not limited to lower performance by the ISA.
    - sylware 2mo ago
      So RISC-V is 'dragged down' because it cannot access the best silicon process (hardware big tech is hogging production capacity... how convenient...)
- camel-cdr 2mo ago
  I think it will be closer to Zen 1/2
- 2mo ago

mosura 2mo ago

> it sounds like there are fundamental issues that prevent performant implementations? This has always been true, it is just this is one of those projects that gets some people very emotionally invested so such discussions do not happen in public. See also Android, rust, webassembly, webgpu and so on.

muyuu 2mo ago

the main problem with RISC-V is also the main selling point: there is no single owner company behind steering development and making sweeping decisions how will that pan out over the long term is really unclear and the reality is performance is actually catching up quickly

LeFantome 2mo ago
History tells us that open standards pretty much always beat out proprietary ones in the end. You cannot buy the company backing RISC-V to take out the competition. And if a RISC-V company stumbles, the ecosystem carries on. But if even one RISC-V company is in the right place at the right time, RISC-V can surge ahead. It is hard to imagine it does not dominate eventually.
- genxy 2mo ago
  Which is really the subtext to Grinberg's rant. It has technical flaws that he dislikes, but those won't stop RISC-V from dominating in the market. You get these kinds of responses when something is too close to perfection. It suddenly gets judged in a much different light.
- windward 2mo ago
  I don't agree with history telling us that at all. HDMI, MP3, MPEG, .docx, DirectX, CUDA, I'm sure there are more. History tells us that money wins. But I also think this is an example of a slight disingenuity in RISC-V being referred to as open-source. It's borrowing the clout of open-source software projects where the end user has the freedom to compile them at home. I can't fabricate a CPU at home, I'm still beholden to whatever patents the manufacturer chooses to license. SiFive have a >billion dollar valuation, for a business based on selling licences.
  - vachina 2mo ago
    Those standards are adopted because they work. And they work because someone poured in tons of RnD to make them work. And those people are incentivised to do the RnD because they get paid (patents). Nowadays nobody will want to work on foundational open source work for free only to enrich everyone else that builds on top of it.

madushan1000 2mo ago

x86 is a horrible architecture, but most of the modern high performance processors are x86. They're only now getting around to making comparatively performant ARM chips. Not having decently performing risc-v chips right now doesn't mean anything other than nobody spent enough time and money on accomplishing that.

dmitrygr 2mo ago

With enough effort, you can make a brick fly. X86 proves this. But if you are designing a new flying device, despite the fact that you could make a brick fly, you probably don’t want to design a brick. Why make it harder on yourself? Riscv took all this information in, and designed a very, very good brick.

ant6n 2mo ago
Wait, so RiscV is still also a brick, like x86?
- dmitrygr 2mo ago
  in my opinion, yes. Given that it was a clean-sheet design with no legacy to support, and that it was done so recently as to have easily had the benefit of all the lessons of x86, mips, arm, sparc, powerpc, etc, yes, it left a lot of obvious improvements on the table.
crote 2mo ago
When everyone is trying to make bricks fly, having the most aerodynamic brick probably isn't a bad thing.

LeFantome 2mo ago

> China was investing heavily in RISC-V, which implies that either they're going to have to settle for permanently crippled perf Not quite. RISC-V application class processors are a new development. They are starting from behind but they are improving faster than the competition. The SpacemiT K3 is 4 times faster than the K1 for example. The Alibaba C950 will be about Apple M1 level performance. And even faster designs are already in the works. RISC-V is not “permenantly crippled”. It will catch up and maybe surpass ARM. It is more an economy of scale issue than anything.

hylaride 2mo ago
My understanding is that RISC-V needs both economies of scale AND chips that are manufactured at the bleeding edge fabs (smallest dies, etc) which is a lot more expensive. It's a chicken and egg problem as there's not (yet?) demand. The architectural limitations will remain until there's incentive to work on it. In many ways it's not much different than Linux was in the 1990s. It was cheap and useful, but often not as performant as commercial OSes (UNIX or even windows) until big corporate money came in and started piling resources into it. Distribution fragmentation was also an issue, which could still cause headaches for RISC-V (especially if some companies start adding proprietary performance extensions that others can't). So I think it remains to be seen how RISC-V will pan out (eg will the cloud vendors see enough of an ROI supporting it for higher end computing than buying ARM licences).
- RetroTechie 2mo ago
  > RISC-V needs both economies of scale AND chips that are manufactured at the bleeding edge fabs (smallest dies, etc) which is a lot more expensive. It's a chicken and egg problem as there's not (yet?) demand Whatever leading-edge fab capacity (mostly TSMC) was available, is now tied up to supply the ongoing AI boom. And will remain so for the foreseeable future. Even if you'd have a RISC-V product for which demand/economics work out, chances are those fabs' order books are filled. Also: design is done in many places, but actual fabrication of RISC-V SoCs in largely centered in China. Which (afaik) doesn't lack IC fabrication capacity. But does lag in leading-edge fab capacity. So: off to older nodes. Which may hurt perf/W, cost effectiveness or transistor budget. Or pay a premium (pricing products out of markets), limited production, or long lead times. Of course this affects ARM based & other products too. But they've been in the optimization / mass fabrication / distribution pipeline much longer than most RISC-V based products. Catching up takes time, and top-tier fab capacity being swiped by Nvidia & co doesn't help to shorten that process. I don't think it's a demand problem. Consumers don't care what powers their phone/tablet/laptop as long as it does its job. So in principle the market is there (yeah.. I understand issues like Google still working on Android-RISC-V, Windows users probably wanting x86 for legacy software etc).

imtringued 2mo ago

So far the vast majority of complaints have been nothing burgers. The biggest valid complaint is the lack of dedicated mask registers for vector processing, that's a huge design flaw in the vector instructions since it makes register renaming and shadow registers mandatory. In other words, the problem here is that they didn't stick with the RISC philosophy of making everything explicit. Compressed instructions are mostly wasted encoding space, but from a performance perspective they don't matter. If they are slow then compilers will treat them as slow legacy instructions and stop using them or they will only emit aligned compressed instructions.

bsder 2mo ago

> I always thought that was a case of "the tech is still catching up",[0] but it sounds like there are fundamental issues that prevent performant implementations? Yes, the fundamental problem is the fact that everybody involved in RISC-V wants to sell IP instead of a chip. The problem with the RISC-V chips in non-embedded contexts (ie desktop or server) has absolutely nothing to do with the instruction set architecture (not entirely true but a really good first approximation). The problem is that performance is strongly dependent upon your high speed interfaces--memory, graphics, PCI, etc. And those blocks need to be strongly integrated in with your CPU interfaces. However, if you buy a whole bunch of IP blocks and then just wire them together, your performance is going to be sub-par. And this is what every single RISC-V chip that I know of currently is. It's not beyond someone to sit down and do the required integration like Apple did for ARM. There's just insufficient money in it so nobody is going to expend the engineers.