Patches for Linux posted on Thursday by Intel prepare for a new version of Speed Select Technology Turbo Frequency (SST-TF) handling for future processors with more cores.
The patches against the Intel x86 ISST driver are in preparation for a new “revision 2” of Speed Select Technology Turbo Frequency (TF) and Performance Profile (PP) to be found on future Intel processors.
I haven’t been able to find any public documentation around the SST-TF v2 changes coming besides what the patch acknowledges that it’s preparing for higher CPU core counts:
“SST-TF revision 2 supports a higher number of cores per bucket, as the current limit of 256 cores may be insufficient. To accommodate this, a new offset, “SST_TF_INFO-8,” is introduced, allowing for a higher core count. Utilize this offset instead of the current “SST_TF_INFO-1″ offset, based on SST-TF revision 2 or higher, and if there is a non-zero core count in any bucket.”
Thus adjusting the code for proper Turbo Frequency handling when hitting such cases of 256+ cores per bucket. The notion of “buckets” with SST-TF revolve around cores with different TDP levels. With SST-TF up until now there has just been three different buckets supported for grouping the different TDP power/performance capabilities of different cores. SST-TF v2 thus is needed for when breaching more than 256 cores in a given power “bucket” / grouping of similar cores. With Clearwater Forest expected to deliver 288 cores, these SST preparations are possibly in preparation for it.
As for the SST-PP v2 changes, there are new fabric 1 P0, P1 and PM frequencies now exposed to user-space.
See this patch series for those interested in the updated Speed Select Technology code for the Linux kernel.
