Linux 6.5 To Boast Improved Handling For Intel Hybrid CPUs With Hyper Threading

Going back to last August were Intel patches to help Intel hybrid CPU handling on Linux by avoiding unnecessary task migrations within SMT domains. Coming this summer those Intel patches are finally set to arrive with the Linux 6.5 kernel cycle.

Since last August those Intel patches to the Linux kernel scheduler continued to be refined for helping deal with Intel hybrid CPUs bearing SMT / Hyper Threading. The original patches explained of the existing Linux kernel problem:

"Intel processors that support Intel Turbo Boost Max 3.0 use asym_packing to assign higher priorities to CPUs with higher maximum frequencies. It artificially assigns, however, a lower priority to the higher-numbered SMT siblings to ensure that they are used last.

This results in unnecessary task migrations within the SMT domains.

On processors with a mixture of higher-frequency SMT cores and lower- frequency non-SMT cores (such as Intel hybrid processors), a lower- priority CPU pulls tasks from the higher-priority cores if more than one SMT sibling is busy."

It took months and since the original patches Raptor Lake launched as well, but at least for Linux 6.5 these patches are poised to finally land. The patches as of today were queued into TIP's sched/core Git branch, marking it material for that v6.5 kernel cycle that should kick off in early July but won't be seeing a stable kernel release until mid to late August.

With the v4 patches from April that are what is queued into TIP's sched/core branch, there is also preparations for better handling on Meteor Lake. Meteor Lake needed special handling with its "CPUs of different maximum frequency in more than one die", compared to Alder Lake and Raptor Lake.

It will be fun to benchmark some Intel hybrid CPUs with Hyper Threading to see ultimately what sort of performance impact this yields... Stay tuned.