Bill.Holler wrote: > Do we want to change cpu_idle_init to return failure right away > when Deep C-States are not supported? cpu_idle_init can check > cpu_deep_cstates_supported(). Currently cpudrv queries ACPI for > C-State info even when idle_cpu_no_deep_c is set. I think this is > leftover from before > we had the cpu_deep_idle tunable. > > > Here is a proposal for variable/keyword semantics: > > idle_cpu_no_deep_c: > Disables ACPI query for C-State information. Disables C-states. > Kernel will not report valid C-state information in kstat(s). > Usage: only used to workaround a bug in ACPI, hardware, or > software.
This sounds good. We can have a chance to boot kernel with buggy BIOS. > > cpu_deep_idle: > Do not use C-States for performance reasons. > Kernel can query ACPI. Kernel will still report available C-State > information in various kstat(s). > Usage: disable C-States solely for performance reasons. > Do we see obvious performance difference? From last SPECpower result, we only lost 1%~ performance while we still get 3W~ power saving. IMHO, this may be implemented by PAD, load balance policy could let cpu sleep shorter and not deeper. Or, is there any another reason to introduce this variable? Thanks, -Aubrey
