Create /sys/power/policy_preference, giving user-space the ability to express its preference for kernel based power vs. performance decisions in a single place. This gives kernel sub-systems and drivers a central place to discover this system-wide policy preference. It also allows user-space to not have to be updated every time a sub-system or driver adds a new power/perf knob. policy_preference has 5 levels, from max_performance through max_powersave. Here is how 4 parts of the kernel might respond to those 5 levels: max_performance (unwilling to sacrifice any performance) scheduler: default (optimized for performance) cpuidle: disable all C-states except polling mode ondemand: disable all P-states except max perf msr_ia32_energy_perf_bias: 0 of 15 performance (care primarily about performance) scheduler: default (optimized for performance) cpuidle: enable all C-states subject to QOS ondemand: all P-states, using no bias msr_ia32_energy_perf_bias: 3 of 15 balanced (default) scheduler: enable sched_mc_power_savings cpuidle: enable all C-states subject to QOS ondemand: all P-states, powersave_bias=5 msr_ia32_energy_perf_bias: 7 of 15 powersave (can sacrifice measurable performance) scheduler: enable sched_smt_power_savings cpuidle: enable all C-states, subject to QOS ondemand: disable turbo mode, powersave_bias=10 msr_ia32_energy_perf_bias: 11 of 15 max_powersave (can sacrifice significant performance) scheduler: enable sched_smt_power_savings cpuidle: enable all C-states, subject to QOS ondemand: min P-state (do not invoke T-states) msr_ia32_energy_perf_bias: 15 of 15 Note that today Linux is typically operating in the mode called "performance" above, rather than "balanced", which is proposed to be the default. While a system should work well if left in "balanced" mode, it is likely that some users would want to use "powersave" when on battery and perhaps shift to "performance" on A/C. Please let me know what you think. thanks, Len Brown, Intel Open Source Technology Center _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
