The OS ports are just the tip of a software iceberg, warns Jon Masters. He has spent the last nine years working on a standard version of Red Hat Linux for Arm servers. So far, just two commercial systems have been announced as certified to run it.
The process involved identifying a set of low-level hardware primitives that are assumed in the x86 world for things like how interrupts and power states work. Those de facto standards were articulated in a
50+ page document, then applied to the Arm architecture.
A separate effort documented x86 boot standards across Linux and Windows and applied them to Arm cores. They included obscure but crucial details of BIOS, power, and multiprocessing functions.
“I worry that the excitement of a new thing like RISC-V misses the real problems” of defining such support details, said Masters, who has been working on Linux for Arm servers since 2011.
RISC-V backers “will learn that no one got PCI right in Arm for the first few generations — to do PCI right [in a non-x86 host system] is tricky,” he said.
Server customers want support for both Windows and Linux, said Richard Jones, an emerging technologies specialist at Red Hat who worked on the RISC-V port of Fedora. In addition, they need a single image of an OS kernel and an applications binary interface that remains stable for years, Jones said in a talk at a RISC-V event last year.
A bootstrapped version of 64-bit Debian is available for RISC-V, but the architecture won’t be natively supported in the upcoming version 10 of the code. RISC-V still lacks support for an LLVM compiler, Java, and languages such as Golang and Rust, said a Debian developer at a recent event.
For its part, Arm led the formation of Linaro, a collaboration that has worked for several years on low-level software for servers as well as systems for telcos and the internet of things. Linaro helped pave Arm’s expansion into a wide variety of areas but has required dedicated engineering time from a wide variety of members at an estimated cost of $100 million.
RISC-V “needs standards and something like a Linaro, and they know this,” said Masters. China’s burgeoning interest in RISC-V could accelerate such efforts, perhaps collapsing them to a five-year journey. However, the opportunity for servers is arguably closing with two strong x86 companies and Arm server alternatives available from Ampere, Cavium, and Huawei, he said.
“Cloud server vendors are hedging their bets with Arm, but they don’t want 10 alternatives, so I’m not sure a RISC-V server opportunity really exists,” said Masters. “I’m sure startups will get funded, but I think they will build domain-specific accelerators.”