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SubjectRe: [linux-pm] RFC: /sys/power/policy_preference
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On Jun 16, 2010, at 4:05 PM, Len Brown <lenb@kernel.org> wrote:

> 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.

I would prefer documenting all the current knobs and adding them to pm-
utils so that pm-powersave knows about and can manage them. Once that
is done, creating arbitrary powersave levels should be fairly simple.

> 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@lists.linux-foundation.org
> https://lists.linux-foundation.org/mailman/listinfo/linux-pm


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