Chimera Linux ghosts RISC-V because there's no time for sluggish hardware

Dev behind the GNU-free distro says boards too slow for serious work

Updated The creators of the unique Chimera Linux distro are dropping support for RISC-V because kit built on the open instruction set architecture just isn't fast enough and this is holding up the development pipeline.

Chimera Linux (not to be confused with the gaming-focused ChimeraOS) is a highly unconventional Linux distro. For one thing, it's GNU-free. For a small project that's not yet reached version 1.0, it has exceptionally wide platform support: x86-64, Arm64, both little-endian and big-endian PowerPC, and RISC-V. Or RISC-V until now.

We took a look at this new distro just over two years ago. It has some ambitious goals. Most of Chimera Linux's userland originates from FreeBSD. Notably, it's not related to Alpine Linux, even though it does use that distro's apk packaging tools and the same musl C library. The platform support is especially impressive given its release status – it only entered beta at the end of last year.

A week ago, the project lead asked on Mastodon: "Would anyone be mad if I actually dropped riscv64 support" – followed the next day by an announcement titled "Dropping RISC-V support," which says:

I had obtained a SiFive HiFive Unmatched board in October 2021 and this proved to be useless for builds as the performance of this board is similar to Raspberry Pi 3.

The post itemized the available RISC-V hardware that they've evaluated, highlighting just one as potentially suitable for their build farm:

Milk-V Pioneer is a board with 64 out-of-order cores; it is the only of its kind, with the cores being supposedly similar to something like ARM Cortex-A72.

If you're tempted by the spec, prepare to be tantalized if you click the Buy Now link. Only one of the three sites says that hardware is available – and even then, only for pre-order. Since then, another Mastodon post says that they've got remote access to one of these now, but it's still proving tricky.

There's more discussion about the performance problems, including things like how to build a miniature build farm, in the Lobsters discussion of the move (for reference, "Q66" is Chimera developer Nina Kolesa).

Their assessment of the availability of RISC-V kit with decent performance matches that of The Reg FOSS desk, as we mentioned back in 2022. The reasonably priced hardware is slow, and the hardware that is respectably quick is not cheap, and despite that, hard to get. When we tried a Framework laptop with a RISC-V mainboard late last year, our assessment was similar. It felt akin to a Raspberry Pi 3 – usable if you're patient, but still sluggish.

One of the ardent defenders of RISC-V in that thread, and other places, is long-time Register commenter Bruce Hoult, who noted problems due to US sanctions, as The Register covered back in January. He told us:

Sophgo were on the verge of taping out the SG2380 with 16 SiFive P670 cores (equivalent to Arm A78) plus eight SiFive X280 cores (dual issue in-order but high performance vector unit with 512 bit vectors) as an NPU.

Had the sanctions not been applied, Sophgo would almost certainly have had test chips some time ago and possibly be close to mass production by now.

That seems like a significant missed opportunity, but major shifts are taking place worldwide, and far worse things than a CPU not launching have happened. The Register has looked at Chinese Linux distros before and there are some aspects there to admire. It will be interesting to see if this grows to extend to CPUs as well. ®

Updated to add at 1539 UTC, March 21

Chimera Linux's RISC-V support has got a stay of execution.

In a lovely example of smaller Linux distros helping one another out, Zach van Rijn, co-developers of the also musl-libc-based Adélie Linux has given Chimera's developer remote access to a Milk-V Pioneer machine:

The performance is fairly acceptable, though nowhere near my original idea of being similar to Cortex-A72; the cores are more comparable to Cortex-A55 in practical performance, especially since we have to disable vectors. As there is still 64 of them, most of the large projects build fairly fast (anything written in Rust builds very slowly, however).

According to recent Mastodon posts, it's running Fedora 38 and they've faced some issues, but Kolesa now has builds running.