POWER Updates For Linux 4.17 Drop POWER4 CPU Support

In addition to Linux 4.17 dropping eight obsolete CPU architectures, this next kernel release is also doing away with POWER4 CPU support.

The IBM POWER4 architecture dates back to 2001 for RS/6000 and AS/400 computers with just above 1.0GHz clock frequencies, dual cores, and around a 115 Watt TDP. POWER4 was succeeded by POWER5 in 2004. While POWER4 and POWER4+ support is removed, PowerPC 970 and POWER5 and newer support remains.

It turns out back in 2016, the POWER4 CPU support was accidentally broken and with no one noticing the past two years, developers have decided to just do away with this older PowerPC architecture. This frees up some maintenance burden and "blocked use of some modern instructions."

The POWER architecture updates for Linux 4.17 also include support now for up to 4 petabytes of user-address space in 64-bit mode, hypervisor support for Transactional Memory on POWER9, other POWER9 improvements, NUMA-aware improvements with the Radix MMU, and more.

The complete list of POWER updates for Linux 4.17 can be found via this PR.

In case you missed it from a few days ago, check out our POWER9 vs. EPYC vs. Xeon benchmarks.