Comment by andai
5 hours 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.
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[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!
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.
> 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-...
[1] https://bolt.graphics/
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
> 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.
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.
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.
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.
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.
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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.
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
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.
> 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.