Linux 5.9 Bringing IBM POWER "System Call Vectored" Support

The Linux 5.9 kernel is set to introduce support for the new IBM POWER System Call Vectored (SCV) ABI with the new SCV and RFSCV instructions. These new instructions can help with performance.

POWER9 / POWER ISA 3.0 supports System Call Vectored (SCV) but to date has not been supported by the mainline Linux kernel. That finally is set to happen with Linux 5.9 with the SCV support being queued in the PowerPC-next tree.

As for the functionality of SCV, "the benefit of these instructions is performance (trading slower SRR0/1 with faster LR/CTR registers, and entering the kernel with MSR[EE] and MSR[RI] left enabled, which can reduce MSR updates. The scv instruction has 128 levels (not enough to cover the Linux system call space)."

This SCV support is queued and ready to go finally with Linux 5.9.

Along with the SCV support, Linux 5.9 is set to bring POWER10 performance monitoring support. This follows various IBM POWER10 plumbing already in place in recent kernels as well as other areas of the stack like GCC. POWER10 7nm CPUs are still reportedly set to launch this year.