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intel_pstate: Add a few comments
Add a few comments in the code which calculates busyness to clarify parts of the algorithm. Signed-off-by: Kristen Carlson Accardi <kristen@linux.intel.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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1 changed files with 31 additions and 1 deletions
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@ -199,7 +199,14 @@ static signed int pid_calc(struct _pid *pid, int32_t busy)
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pid->integral += fp_error;
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/* limit the integral term */
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/*
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* We limit the integral here so that it will never
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* get higher than 30. This prevents it from becoming
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* too large an input over long periods of time and allows
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* it to get factored out sooner.
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*
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* The value of 30 was chosen through experimentation.
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*/
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integral_limit = int_tofp(30);
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if (pid->integral > integral_limit)
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pid->integral = integral_limit;
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@ -616,6 +623,11 @@ static void intel_pstate_get_min_max(struct cpudata *cpu, int *min, int *max)
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if (limits.no_turbo || limits.turbo_disabled)
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max_perf = cpu->pstate.max_pstate;
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/*
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* performance can be limited by user through sysfs, by cpufreq
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* policy, or by cpu specific default values determined through
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* experimentation.
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*/
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max_perf_adj = fp_toint(mul_fp(int_tofp(max_perf), limits.max_perf));
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*max = clamp_t(int, max_perf_adj,
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cpu->pstate.min_pstate, cpu->pstate.turbo_pstate);
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@ -717,11 +729,29 @@ static inline int32_t intel_pstate_get_scaled_busy(struct cpudata *cpu)
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u32 duration_us;
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u32 sample_time;
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/*
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* core_busy is the ratio of actual performance to max
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* max_pstate is the max non turbo pstate available
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* current_pstate was the pstate that was requested during
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* the last sample period.
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*
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* We normalize core_busy, which was our actual percent
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* performance to what we requested during the last sample
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* period. The result will be a percentage of busy at a
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* specified pstate.
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*/
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core_busy = cpu->sample.core_pct_busy;
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max_pstate = int_tofp(cpu->pstate.max_pstate);
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current_pstate = int_tofp(cpu->pstate.current_pstate);
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core_busy = mul_fp(core_busy, div_fp(max_pstate, current_pstate));
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/*
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* Since we have a deferred timer, it will not fire unless
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* we are in C0. So, determine if the actual elapsed time
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* is significantly greater (3x) than our sample interval. If it
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* is, then we were idle for a long enough period of time
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* to adjust our busyness.
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*/
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sample_time = pid_params.sample_rate_ms * USEC_PER_MSEC;
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duration_us = (u32) ktime_us_delta(cpu->sample.time,
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cpu->last_sample_time);
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