Public bug reported: This issue is explained and discussed in detail on the linux-acpi mailing list in the following three threads:
* Initial issue report: https://lore.kernel.org/linux-acpi/d01b0a1f-bd33-47fe-ab41-43843d8a3...@kfocus.org/T/#u * First patch submitted to mainline for review: https://lore.kernel.org/linux-acpi/202406190206.z56zezty-...@intel.com/T/#t * Second patch (not mine) submitted to mainline for review: https://lore.kernel.org/linux-acpi/8f97bab7-c504-4d8c-977b-44f20b4c1...@amd.com/T/#t Intel-based machines using heterogeneous-core processors (i.e., anything with P-cores and E-cores) require Intel Turbo Boost Max Technology 3.0 (ITMT) in order for the EEVDF scheduler to correctly assign intensive single-core loads to P-cores. If ITMT is not enabled, the scheduler does not get hints about CPU performance differences, causing it to oftentimes schedule single-core workloads on E-cores rather than P-cores. This leads to a serious drop in single-core performance. Currently, if CPPC v2 is not acked by the firmware, the intel_pstate driver will *not* enable ITMT. This means that any device with a hybrid- core Intel CPU, where CPPC v2 is missing, non-functional, or incorrectly disabled by the firmware, will experience the performance drop mentioned above. This happens in the wild: * My workplace, Kubuntu Focus, is affected by this issue: https://lore.kernel.org/linux-acpi/d01b0a1f-bd33-47fe-ab41-43843d8a3...@kfocus.org/T/#u * A user of a Star Labs laptop was also affected: https://github.com/StarLabsLtd/firmware/issues/143 * Someone on the Manjaro forums appears to have run into this potentially: https://forum.manjaro.org/t/linux-kernel-6-6-lts-cpu-regression-on-i7-alderlake/157474 * Someone onf the Gentoo forums also may have run into this: https://forums.gentoo.org/viewtopic-p-8819389.html?sid=5997f89fd5a202b6db8396fba0b45821 This issue, as shown above, has been discussed on the linux-acpi mailing list, and currently has a fix in the works. https://lore.kernel.org/linux- acpi/8f97bab7-c504-4d8c-977b-44f20b4c1...@amd.com/T/#t The fix works by falling back to using info from MSR_HWP_CAPABILITIES in the event CPPC is not available. ** Affects: linux (Ubuntu) Importance: Undecided Status: New -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/2069988 Title: intel_pstate fails to enable ITMT if CPPC v2 is disabled by firmware, resulting in bad single-core performance on some heterogeneous-core Intel systems To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2069988/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
