Ubuntu 25.10 Raises RISC-V Profile Requirements(omgubuntu.co.uk)
omgubuntu.co.uk
Ubuntu 25.10 Raises RISC-V Profile Requirements
https://www.omgubuntu.co.uk/2025/06/ubuntu-riscv-rva23-support
52 comments
The original two generations of iPhone were armv6 with hardware floating point, so that always felt to me like the sane baseline. Android wasn't using hardware floating point on armv6, but I think that was only because the compilers they had sucked (an issue that didn't apply to Apple), and many/most of the devices in fact shipped with the same hardware. I dunno... like, I don't know exactly what went into Debian's decision there, but I could see it having been made for the wrong reasons: looking at what software had been deployed rather than what hardware was common?
I was there when people were building a cross distro consensus, and the discussion was as I recall basically about hardware. By definition the software deployed was built using the previous set of distro baselines, and this being Linux the assumption is that you just recompile from source. (There was also ongoing work in parallel to add inline neon asm implementations where needed for feature/performance parity with x86.)
Android and iOS were not relevant at all, since for Android targets Google were free to pick whatever compiler config they liked and Apple is its own thing, and neither group of phones was on the table as targets for Linux distros.
The driver behind picking armv7 was:
- clearly we need some new baseline that isn't the lowest common denominator, so we take advantage of the FPU
- distros don't have the resources to want to build for lots of targets at once
- armv7 will work for new hardware, and there's not that much armv6 stuff out there, so it can live with continuing to use the armv5 builds
- there do seem to be deployed chips with only VFPv3d16 and no Neon (notably the Tegra chips), so we will not require Neon, so they can also use the new baseline
It's just really unfortunate that the rpi chose a trailing edge CPU for essentially "we happened to have this" reasons and then it blew up to become a super popular board because they got the price point and the ecosystem support right.
Android and iOS were not relevant at all, since for Android targets Google were free to pick whatever compiler config they liked and Apple is its own thing, and neither group of phones was on the table as targets for Linux distros.
The driver behind picking armv7 was:
- clearly we need some new baseline that isn't the lowest common denominator, so we take advantage of the FPU
- distros don't have the resources to want to build for lots of targets at once
- armv7 will work for new hardware, and there's not that much armv6 stuff out there, so it can live with continuing to use the armv5 builds
- there do seem to be deployed chips with only VFPv3d16 and no Neon (notably the Tegra chips), so we will not require Neon, so they can also use the new baseline
It's just really unfortunate that the rpi chose a trailing edge CPU for essentially "we happened to have this" reasons and then it blew up to become a super popular board because they got the price point and the ecosystem support right.
You can look at Debian's reasoning here: https://wiki.debian.org/ArmHardFloatPort. As I understand, the decision was mostly based on hardware.
I might be missing it, but, after going through that entire page, the only things I am seeing that are relevant are the following four sentences, and none of them provide a rationale?
> Currently the Debian armhf port requires at least an Armv7 CPU with Thumb-2 and VFP3D16.
> It might make sense for such a new port -- which would essentially target newer hardware -- to target newer CPUs. For instance, it could target Armv6 or Armv7 SoCs, and VFPv2, VFPv3-D16 or NEON.
> In practice armel will be used for older CPUs (armv4t, armv5, armv6), and armhf for newer CPUs (armv7+VFP).
> Some concern for fast-enough, pretty awesome (600MHz+) Armv6 + VFPv2 processors here - i.MX37 etc. - which will not be supported by armhf default flavour, but.. we will have to live with that
> Currently the Debian armhf port requires at least an Armv7 CPU with Thumb-2 and VFP3D16.
> It might make sense for such a new port -- which would essentially target newer hardware -- to target newer CPUs. For instance, it could target Armv6 or Armv7 SoCs, and VFPv2, VFPv3-D16 or NEON.
> In practice armel will be used for older CPUs (armv4t, armv5, armv6), and armhf for newer CPUs (armv7+VFP).
> Some concern for fast-enough, pretty awesome (600MHz+) Armv6 + VFPv2 processors here - i.MX37 etc. - which will not be supported by armhf default flavour, but.. we will have to live with that
I just read it, seems like an unfortunate chain of events. They tried to look forward a little bit by looking at the current generation of hardware that’s out there, and didn’t anticipate an older chip to become that massively popular.
The Debian call seemed odd given the hardware on the market at the time - armv6 was on some very popular devices already.
In contrast, RISCV is still much more niche right now, & from the selection that is out there, DeepComputing FML13V01 & Pine64 both support Ubuntu 25 already, so they do seem to be banking on hardware that's already extant rather than pushing against the grain.
In contrast, RISCV is still much more niche right now, & from the selection that is out there, DeepComputing FML13V01 & Pine64 both support Ubuntu 25 already, so they do seem to be banking on hardware that's already extant rather than pushing against the grain.
If your arbitrary scenario comes to pass, it's software, not a bridge, or a fleeting hype bubble to pull money out of. They can patch in what they need. This keeps the TODOs concrete for the team.
Missed opportunity in software does not have the same consequence long term as missing out a $2 million gain if only you'd held those stonks a bit longer.
Missed opportunity in software does not have the same consequence long term as missing out a $2 million gain if only you'd held those stonks a bit longer.
RVA23 is actually a decent ISA for linux machines for the long term, RVA20 was not.
Presumably there's going to be some hardware releases later this year that Ubuntu has early knowledge of.
Does this line up with what riscv android will also require?
Presumably there's going to be some hardware releases later this year that Ubuntu has early knowledge of.
Does this line up with what riscv android will also require?
Yeah, the RISC-V community itself didn't see it as sufficient to build a competitive chip with until RVA23. The relevant milestones have been worked on for years. A LOT of effort was spent to get them right because ISA standards are hard to undo.
RISC-V has been perfectly suitable for embedded use and RISC-V is killing in that market.
But none of the Linux capable hardware produced up to this point has been competitive with existing alternatives. No one was seriously thinking that the OrangePi was a better value than an RPi.
These computers were primarily useful as dev boards to start porting software. The manufacturers are trying to scale manufacturing and establish market share, not turn a big profit. They knew their v1 hardware would be buggy and short lived. The CPUs themselves have been busy speed running the complexity levels that ARM and x86 had decades to develop.
RISC-V has been perfectly suitable for embedded use and RISC-V is killing in that market.
But none of the Linux capable hardware produced up to this point has been competitive with existing alternatives. No one was seriously thinking that the OrangePi was a better value than an RPi.
These computers were primarily useful as dev boards to start porting software. The manufacturers are trying to scale manufacturing and establish market share, not turn a big profit. They knew their v1 hardware would be buggy and short lived. The CPUs themselves have been busy speed running the complexity levels that ARM and x86 had decades to develop.
>Does this line up with what riscv android will also require?
AIUI both Google and Microsoft selected RVA23 as baseline.
AIUI both Google and Microsoft selected RVA23 as baseline.
Google quote from https://riscv.org/riscv-news/2024/10/risc-v-announces-ratifi...
> "Google is delighted to see the ratification of the RVA23 Profile," said Lars Bergstrom, Director of Engineering, Google. "This profile has been the result of a broad industry collaboration, and is now the baseline requirement for the Android RISC-V Application Binary Interface (ABI)."
> "Google is delighted to see the ratification of the RVA23 Profile," said Lars Bergstrom, Director of Engineering, Google. "This profile has been the result of a broad industry collaboration, and is now the baseline requirement for the Android RISC-V Application Binary Interface (ABI)."
> RVA23 is actually a decent ISA for linux machines for the long term, RVA20 was not.
This is setting it all up to happen again with whatever is found to be wrong with RVA23.
This is setting it all up to happen again with whatever is found to be wrong with RVA23.
RVA20 was missing generally expected features, RVA23 isnt
RVA30 is N+1, presumably we wont see shipping devices for that until the early 2030s
RVA30 is N+1, presumably we wont see shipping devices for that until the early 2030s
Seems unlikely.
> that Ubuntu has early knowledge of.
They aren’t big enough to get advance notice of hardware from any serious SoC makers. So I bet not.
They aren’t big enough to get advance notice of hardware from any serious SoC makers. So I bet not.
Still, no consumer based RV23 mini-ITX or micro-ATX or ATX form factor devices.
And Orange PI 2 has a GFX blob issue.
And Orange PI 2 has a GFX blob issue.
It's worse than that -- there is not a single piece of hardware that implements RVA23 available to be bought on the market today.
There are SoCs on the market that implement RVV (Vector extensions), and SoCs on the market that implement H (Hypervisor extensions).
There are no SoCs on the market that implement both at the same time. And both are mandatory for RVA23.
I'd love to be proven wrong on the hardware availability. If there's hardware to be bought in western countries that implements both RVV and H, please let me know.
There are SoCs on the market that implement RVV (Vector extensions), and SoCs on the market that implement H (Hypervisor extensions).
There are no SoCs on the market that implement both at the same time. And both are mandatory for RVA23.
I'd love to be proven wrong on the hardware availability. If there's hardware to be bought in western countries that implements both RVV and H, please let me know.
> It's worse than that -- there is not a single piece of hardware that implements RVA23 available to be bought on the market today.
I think that's fine, as an outsider without any RISC-V board around, alignment in the future seems better than a board out today given performance is AFAIK still awfully subpar.
As a potential consumer all I want is that by the time RISC-V really hits the market people don't start hitting edge cases like toes on furniture with missing extensions that ended up being critical to properly run the software they need. I don't want another shitshow like USB-C fast-charging where consumers can't easily tell if a cable will work fine or end up in a slow charge fallback.
I'd rather see RISC-V for the more general public coming out later than starting with the wrong foot.
I think that's fine, as an outsider without any RISC-V board around, alignment in the future seems better than a board out today given performance is AFAIK still awfully subpar.
As a potential consumer all I want is that by the time RISC-V really hits the market people don't start hitting edge cases like toes on furniture with missing extensions that ended up being critical to properly run the software they need. I don't want another shitshow like USB-C fast-charging where consumers can't easily tell if a cable will work fine or end up in a slow charge fallback.
I'd rather see RISC-V for the more general public coming out later than starting with the wrong foot.
>Still, no consumer based RV23 mini-ITX or micro-ATX or ATX form factor devices.
Sure. But there are RVA22+V such devices. RVA23 will eventually succeed these.
Many IP vendors announced RVA23 cores, but understand that the process from having a core design available for licensing to having a chip is very long, measured in years.
Among the designs that are further down in the pipeline of development, a highlight is Tenstorrent's Ascalon. According to them, a tapeout is "imminent". This was in the RISC-V Summit EU a few weeks ago. That'd mean RVA23 chips competitive with Zen5 in early 2026.
Sure. But there are RVA22+V such devices. RVA23 will eventually succeed these.
Many IP vendors announced RVA23 cores, but understand that the process from having a core design available for licensing to having a chip is very long, measured in years.
Among the designs that are further down in the pipeline of development, a highlight is Tenstorrent's Ascalon. According to them, a tapeout is "imminent". This was in the RISC-V Summit EU a few weeks ago. That'd mean RVA23 chips competitive with Zen5 in early 2026.
> That'd mean RVA23 chips competitive with Zen5 in early 2026
allegedly competitive, according to the vendor who is not impartial and with no actual benchmarks in existence to prove anything.
allegedly competitive, according to the vendor who is not impartial and with no actual benchmarks in existence to prove anything.
None of them are competitive with Zen5 on a per core basis, if you compare the published SPEC results.
Veyron V2 has comparable perf per GHz to Zen4/5, but at a lower clock frequency (N4: 3.25, N3: 3.85): https://www.ventanamicro.com/technology/risc-v-cpu-ip/
Ascalon is about half as fast as Veyron V2, partially due to lower clock frequency (~2.6 GHz): https://riscv.or.jp/wp-content/uploads/Japan_RISC-V_day_Spri... It's really more designed as a "we need a decently fast and efficient CPU for our AI accelerator" then a "let's build the fastes CPU possible".
Veyron V2 has comparable perf per GHz to Zen4/5, but at a lower clock frequency (N4: 3.25, N3: 3.85): https://www.ventanamicro.com/technology/risc-v-cpu-ip/
Ascalon is about half as fast as Veyron V2, partially due to lower clock frequency (~2.6 GHz): https://riscv.or.jp/wp-content/uploads/Japan_RISC-V_day_Spri... It's really more designed as a "we need a decently fast and efficient CPU for our AI accelerator" then a "let's build the fastes CPU possible".
This is not a problem.
We are not running supercomputers at home.
We need to be able Math software on modern open hardware We need to be able to program with a better assembly We need to be able to have predictable code generation from our compilers We need to play with a new architecture and port software as an exercise We need to have choice
We are not running supercomputers at home.
We need to be able Math software on modern open hardware We need to be able to program with a better assembly We need to be able to have predictable code generation from our compilers We need to play with a new architecture and port software as an exercise We need to have choice
We did just fine without those for many decades.
It is the openess religion that eventually loses sight of what customers and businesses alike care about and keep alive on the market.
It is the openess religion that eventually loses sight of what customers and businesses alike care about and keep alive on the market.
Can you write a kernel patch / driver to trap the unsupported instructions and provide software implementations?
The profile includes not just additional instructions but also architectural requirements that can't be emulated. The size of cache lines and reservation sets must be 64 bytes (there is no instruction to query it, like there is on ARM).
Data-independent execution latency is important for protecting cryptography against timing attacks.
Those were already in RVA22, and the difference from that to RVA23 could probably be emulated with traps though.
However, I think that some of the new instructions in RVA23 may potentially become very common in some binaries later on and could possibly trap so often that they would slow down those programs considerably.
Those were already in RVA22, and the difference from that to RVA23 could probably be emulated with traps though.
However, I think that some of the new instructions in RVA23 may potentially become very common in some binaries later on and could possibly trap so often that they would slow down those programs considerably.
> The size of cache lines and reservation sets must be 64 bytes (there is no instruction to query it, like there is on ARM)
Thank goodness. What a colossal PITA trying to account for that across cluster switches.
Thank goodness. What a colossal PITA trying to account for that across cluster switches.
> the difference from that to RVA23 could probably be emulated with traps though
There is no way you want to be trapping basic things such as `c.lb{u}` and `c.sb` and `c.{s,z}ext.{b,h,w}` which are going to be thoroughly mixed in all over the place.
There is no way you want to be trapping basic things such as `c.lb{u}` and `c.sb` and `c.{s,z}ext.{b,h,w}` which are going to be thoroughly mixed in all over the place.
Couldn't one completely disable cache thereby forcing a worst-case timing?
Rva20 lacks vector support and hypervisor instructions, among other things.
You’re welcome to put a ton of effort in for dogshit performance on a bunch or $35 SBCs but the rest of us will just upgrade
And don’t worry, some vendor won’t come in and magically save you - fedora is eyeing rv22 as their baseline.
You’re welcome to put a ton of effort in for dogshit performance on a bunch or $35 SBCs but the rest of us will just upgrade
And don’t worry, some vendor won’t come in and magically save you - fedora is eyeing rv22 as their baseline.
The Linux Kernel has math coprocessor emulation (mainly floating point stuff) that can be enabled if your CPU doesn't include it. This was common with consumer CPUs in the 1990s and some embedded CPUs today.
Link here, although I'm sure it existed well before 2.6.12
https://www.kernelconfig.io/config_math_emulation
Link here, although I'm sure it existed well before 2.6.12
https://www.kernelconfig.io/config_math_emulation
That's the problem with open source, a bunch of people who once in their life want to "do it right" (right never comes). No adults in the room to say "this is what you got".
From a billion python packages in distribution package managers to broken screen sharing in Wayland, "right" isn't even what anyone wants.
From a billion python packages in distribution package managers to broken screen sharing in Wayland, "right" isn't even what anyone wants.
Can you rephrase your answer in a way that isn't brutally and unnecessarily hostile?
Honestly, it's because of the "can you do a ton of unpaid work to support my niche, non-commercial application" attitude of the OP, which I find to be extremely distasteful.
It's something I deal with frequently. I should not have taken it out on OP and I agree I could have communicated that much better.
Unfortunately, I can't edit my post or I would rephrase it significantly.
Sorry to user "Levitating", I was being a dick.
It's something I deal with frequently. I should not have taken it out on OP and I agree I could have communicated that much better.
Unfortunately, I can't edit my post or I would rephrase it significantly.
Sorry to user "Levitating", I was being a dick.
> Honestly, it's because of the "can you do a ton of unpaid work to support my niche, non-commercial application" attitude of the OP, which I find to be extremely distasteful.
I understood their "Can you" as "Can one [theoretically]", more on the curiosity side than on the entitled side.
I understood their "Can you" as "Can one [theoretically]", more on the curiosity side than on the entitled side.
I am really hoping there are is some unannounced hardware that Ubuntu is aware of.
Why can't these older processors be supported via a software shim for unrecognised instructions?
It is far better for software to run with a couple of percent slowdown on old cpus only than not run at all.
It is far better for software to run with a couple of percent slowdown on old cpus only than not run at all.
> It is far better for software to run with a couple of percent slowdown on old cpus only than not run at all.
The difference on geekbench is 2x and not every benchmark has been optimized for RVV yet: https://browser.geekbench.com/v6/cpu/compare/10681749?baseli... (same hardware, one using the newer geekbench version that can take advantage of RVA22+V)
The difference on geekbench is 2x and not every benchmark has been optimized for RVV yet: https://browser.geekbench.com/v6/cpu/compare/10681749?baseli... (same hardware, one using the newer geekbench version that can take advantage of RVA22+V)
Because new instructions such as `c.lb{u}` and `c.sb` and `c.{s,z}ext.{b,h,w}` are going to be thoroughly mixed in all over the place. Probably the (kinda) conditional move `czero.eqz` and `czero.nez` too.
>Why can't these older processors be supported via a software shim for unrecognised instructions?
It can.
It's just this shim is out of scope for Ubuntu.
Refer to opensbi instruction emulation.
>It is far better for software to run with a couple of percent slowdown on old cpus only than not run at all.
With features like vector instructions or pointer masking, we're talking a non-trivial slowdown.
It can.
It's just this shim is out of scope for Ubuntu.
Refer to opensbi instruction emulation.
>It is far better for software to run with a couple of percent slowdown on old cpus only than not run at all.
With features like vector instructions or pointer masking, we're talking a non-trivial slowdown.
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This will keep happening as the omissions in the risc v application processor standard are fleshed out.
Holy cow! Ubuntu really takes their hardware gatekeeping seriously.
Of course we'll hear from the apologists about how much extra work supporting "low end" systems is - think of the developers! think of Ubuntu's bottom line!
> Admittedly there is one big rub: the range of RISC-V devices with RVA23 support is, at the time or writing this, near non-existent.
They couldn't even wait for hardware to be available before doing this? So basically Ubuntu 25.10 only runs on hardware that doesn't yet exist. Nice.
> Focusing future Ubuntu support to devices that have more capable RISC-V profile sets will further position the distro as the de-facto OS on the platform.
...or everyone will move to something else - ANYTHING else - because we don't want to replace our brand new devices just to run Ubuntu.
Of course we'll hear from the apologists about how much extra work supporting "low end" systems is - think of the developers! think of Ubuntu's bottom line!
> Admittedly there is one big rub: the range of RISC-V devices with RVA23 support is, at the time or writing this, near non-existent.
They couldn't even wait for hardware to be available before doing this? So basically Ubuntu 25.10 only runs on hardware that doesn't yet exist. Nice.
> Focusing future Ubuntu support to devices that have more capable RISC-V profile sets will further position the distro as the de-facto OS on the platform.
...or everyone will move to something else - ANYTHING else - because we don't want to replace our brand new devices just to run Ubuntu.
>...or everyone will move to something else - ANYTHING else - because we don't want to replace our brand new devices just to run Ubuntu.
Everyone now is nobody tomorrow.
Right now, the few RISC-V boards are in the hands of developers and enthusiasts.
In the future, RISC-V will continue to grow, into mass-market.
Ubuntu recognizes the importance of being able to fully take advantage of RVA23, a fully capable ISA comparable to x86-64v4 and ARMv9.
Everyone now is nobody tomorrow.
Right now, the few RISC-V boards are in the hands of developers and enthusiasts.
In the future, RISC-V will continue to grow, into mass-market.
Ubuntu recognizes the importance of being able to fully take advantage of RVA23, a fully capable ISA comparable to x86-64v4 and ARMv9.
Salespeak ;)
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Debian decided, probably very sensibly at the time, to set their minimum target for their 32 bit arm hardfloat distro to armv7. I guess hardly anyone used armv6 with hardware floating point apart from some obscure Broadcom chip. Then the original Raspberry Pi was released, moved an insane number of units, and Debian users would have been stuck with no hardware floating point. Fortunately Mike Thompson recompiled Debian for armv6 with hardfloat and that Debian fork (Raspbian) ended up becoming the basis for the official Raspberry Pi OS.