On Tue, Jun 20, 2023 at 10:06:25AM -0400, Waiman Long wrote:
When a user sets "intel_idle.max_cstate=0", it will disableUrgh, no, just no. This is nasty.
intel_idle and fall back to acpi_idle instead. The acpi_idle code
will then call mwait_idle_with_hints() to enter idle state. So when
X86_FEATURE_KERNEL_IBRS is enabled, it is necessary to disable IBRS
within mwait_idle_with_hints() when IRQ was disabled to avoid performance
degradation on silbing thread running user workload.