As part of the "smp/core" changes that were merged last week for the Linux 6.6 kernel, partial SMT enablement landed for processors that support more than two threads per physical core to allow greater run-time control over just how many threads to enable.

This partial SMT enablement run-time control support via sysfs has been led by IBM. IBM POWER processors can allow up to 16-way SMT although 4 and 8 threads per core is more common on that front. At boot-time the Linux kernel can already control how many threads per core to bring-up but for those manipulating the SMT configuration at run-time the sysfs interface is extended to allow for only partial SMT enablement.

Linux 6.6 allows writing an integer to /sys/devices/system/cpu/smt/control for controlling the number of SMT threads per core to enable rather than simply toggling it on/off.

More details on this partial SMT enablement run-time control for Linux 6.6 via the smp/core pull .