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Final power management fixes for 3.15
- Taking non-idle time into account when calculating core busy
time was a mistake and led to a performance regression. Since
the problem it was supposed to address is now taken care of in
a different way, we don't need to do it any more, so drop the
non-idle time tracking from intel_pstate. Dirk Brandewie.
- Changing to fixed point math throughout the busy calculation
introduced rounding errors that adversely affect the accuracy
of intel_pstate's computations. Fix from Dirk Brandewie.
- The PID controller algorithm used by intel_pstate assumes that
the time interval between two adjacent samples will always be the
same which is not the case for deferable timers (used by
intel_pstate) when the system is idle. This leads to inaccurate
predictions and artificially increases convergence times for
the minimum P-state. Fix from Dirk Brandewie.
- intel_pstate carries out computations using 32-bit variables
that may overflow for large enough values of APERF/MPERF. Switch
to using 64-bit variables for computations, from Doug Smythies.
/
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Merge tag 'pm-3.15-final' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm
Pull intel pstate fixes from Rafael Wysocki:
"Final power management fixes for 3.15
- Taking non-idle time into account when calculating core busy time
was a mistake and led to a performance regression. Since the
problem it was supposed to address is now taken care of in a
different way, we don't need to do it any more, so drop the
non-idle time tracking from intel_pstate. Dirk Brandewie.
- Changing to fixed point math throughout the busy calculation
introduced rounding errors that adversely affect the accuracy of
intel_pstate's computations. Fix from Dirk Brandewie.
- The PID controller algorithm used by intel_pstate assumes that the
time interval between two adjacent samples will always be the same
which is not the case for deferable timers (used by intel_pstate)
when the system is idle. This leads to inaccurate predictions and
artificially increases convergence times for the minimum P-state.
Fix from Dirk Brandewie.
- intel_pstate carries out computations using 32-bit variables that
may overflow for large enough values of APERF/MPERF. Switch to
using 64-bit variables for computations, from Doug Smythies"
* tag 'pm-3.15-final' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm:
intel_pstate: Improve initial busy calculation
intel_pstate: add sample time scaling
intel_pstate: Correct rounding in busy calculation
intel_pstate: Remove C0 tracking
This commit is contained in:
Linus Torvalds
commit
c717d15614
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@ -40,10 +40,10 @@
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#define BYT_TURBO_VIDS 0x66d
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#define FRAC_BITS 6
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#define FRAC_BITS 8
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#define int_tofp(X) ((int64_t)(X) << FRAC_BITS)
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#define fp_toint(X) ((X) >> FRAC_BITS)
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#define FP_ROUNDUP(X) ((X) += 1 << FRAC_BITS)
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static inline int32_t mul_fp(int32_t x, int32_t y)
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{
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@ -59,8 +59,8 @@ struct sample {
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int32_t core_pct_busy;
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u64 aperf;
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u64 mperf;
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unsigned long long tsc;
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int freq;
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ktime_t time;
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};
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struct pstate_data {
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@ -98,9 +98,9 @@ struct cpudata {
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struct vid_data vid;
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struct _pid pid;
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ktime_t last_sample_time;
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u64 prev_aperf;
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u64 prev_mperf;
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unsigned long long prev_tsc;
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struct sample sample;
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};
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@ -200,7 +200,10 @@ static signed int pid_calc(struct _pid *pid, int32_t busy)
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pid->last_err = fp_error;
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result = pterm + mul_fp(pid->integral, pid->i_gain) + dterm;
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if (result >= 0)
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result = result + (1 << (FRAC_BITS-1));
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else
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result = result - (1 << (FRAC_BITS-1));
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return (signed int)fp_toint(result);
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}
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@ -560,47 +563,42 @@ static void intel_pstate_get_cpu_pstates(struct cpudata *cpu)
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static inline void intel_pstate_calc_busy(struct cpudata *cpu,
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struct sample *sample)
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{
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int32_t core_pct;
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int32_t c0_pct;
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int64_t core_pct;
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int32_t rem;
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core_pct = div_fp(int_tofp((sample->aperf)),
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int_tofp((sample->mperf)));
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core_pct = mul_fp(core_pct, int_tofp(100));
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FP_ROUNDUP(core_pct);
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core_pct = int_tofp(sample->aperf) * int_tofp(100);
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core_pct = div_u64_rem(core_pct, int_tofp(sample->mperf), &rem);
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c0_pct = div_fp(int_tofp(sample->mperf), int_tofp(sample->tsc));
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if ((rem << 1) >= int_tofp(sample->mperf))
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core_pct += 1;
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sample->freq = fp_toint(
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mul_fp(int_tofp(cpu->pstate.max_pstate * 1000), core_pct));
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sample->core_pct_busy = mul_fp(core_pct, c0_pct);
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sample->core_pct_busy = (int32_t)core_pct;
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}
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static inline void intel_pstate_sample(struct cpudata *cpu)
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{
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u64 aperf, mperf;
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unsigned long long tsc;
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rdmsrl(MSR_IA32_APERF, aperf);
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rdmsrl(MSR_IA32_MPERF, mperf);
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tsc = native_read_tsc();
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aperf = aperf >> FRAC_BITS;
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mperf = mperf >> FRAC_BITS;
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tsc = tsc >> FRAC_BITS;
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cpu->last_sample_time = cpu->sample.time;
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cpu->sample.time = ktime_get();
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cpu->sample.aperf = aperf;
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cpu->sample.mperf = mperf;
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cpu->sample.tsc = tsc;
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cpu->sample.aperf -= cpu->prev_aperf;
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cpu->sample.mperf -= cpu->prev_mperf;
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cpu->sample.tsc -= cpu->prev_tsc;
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intel_pstate_calc_busy(cpu, &cpu->sample);
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cpu->prev_aperf = aperf;
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cpu->prev_mperf = mperf;
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cpu->prev_tsc = tsc;
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}
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static inline void intel_pstate_set_sample_time(struct cpudata *cpu)
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@ -614,13 +612,25 @@ static inline void intel_pstate_set_sample_time(struct cpudata *cpu)
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static inline int32_t intel_pstate_get_scaled_busy(struct cpudata *cpu)
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{
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int32_t core_busy, max_pstate, current_pstate;
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int32_t core_busy, max_pstate, current_pstate, sample_ratio;
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u32 duration_us;
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u32 sample_time;
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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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return FP_ROUNDUP(core_busy);
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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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if (duration_us > sample_time * 3) {
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sample_ratio = div_fp(int_tofp(sample_time),
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int_tofp(duration_us));
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core_busy = mul_fp(core_busy, sample_ratio);
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}
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return core_busy;
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}
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static inline void intel_pstate_adjust_busy_pstate(struct cpudata *cpu)
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