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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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