The current crop of RISC-V SoCs are still much slower than alternative CPU architectures and lead to much longer build times for Fedora packages as a result. There’s hope with next-gen RISC-V processors being faster but for now even compiling Binutils as an example is around five times slower than x86_64 — and that’s with disabling compiler link-time optimizations (LTO) for RISC-V to avoid an even longer build process.
Marcin Juszkiewicz of Red Hat who has long specialized in ARM64 Linux has been working on RISC-V package builds for Fedora Linux. His latest blog post on the subject today is entitled “RISC-V is sloooow“.
RISC-V package build times for Linux results in “terrible build times” with GNU Binutils build times used as an example. Compiling Binutils on x86_64 with eight cores is around 29 minutes, with LTO optimizations included, where as building Binutils on RISC-V without LTO is around 143 minutes — and that’s without LTO. The next slowest architecture for building Binutils was POWER PPC64LE at 46 minutes. AArch64 meanwhile came in at 36 minutes and i686 was the fastest at 25 minutes.
Juszkiewicz commented in his blog:
“The UltraRISC UR-DP1000 SoC, present on the Milk-V Titan motherboard should improve situation a bit (and can have 64 GB ram). Similar with SpacemiT K3-based systems (but only 32 GB ram). Both will be an improvement, but not the final solution.
We need hardware capable of building above “binutils” package below one hour. With LTO enabled system-wide etc. And it needs to be rackable and manageable like any other boring server. Without it, we can not even plan for the RISC-V 64-bit architecture to became one of official, primary architectures in Fedora Linux.”
With current RISC-V SoCs being so slow, QEMU is leveraged to help compensate for the slow hardware. Using 80 emulated RISC-V cores can compile LLVM under QEMU in about four hours compared to more than ten hours on a Banana Pi BPI-F3 builder.
Marcin’s blog post concludes with:
“We plan to start building Fedora Linux 44. If things go well, we will use the same kernel image on all of our builders (the current ones use a mix of kernel versions). LTO will still be disabled.
When it comes to lack of speed… There are plans to bring new, faster builders. And probably assign some heavier packages to them.”
