| Message ID | 20220111155419.943980-1-Pierre.Gondois@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Delegated to: | viresh kumar |
| Headers | show |
| Series | [v2] cpufreq: CPPC: Fix performance/frequency conversion | expand |
On Tue, Jan 11, 2022 at 4:54 PM Pierre Gondois <Pierre.Gondois@arm.com> wrote: > > CPUfreq governors request CPU frequencies using information > on current CPU usage. The CPPC driver converts them to > performance requests. Frequency targets are computed as: > target_freq = (util / cpu_capacity) * max_freq > target_freq is then clamped between [policy->min, policy->max]. > > The CPPC driver converts performance values to frequencies > (and vice-versa) using cppc_cpufreq_perf_to_khz() and > cppc_cpufreq_khz_to_perf(). These functions both use two different > factors depending on the range of the input value. For > cppc_cpufreq_khz_to_perf(): > - (NOMINAL_PERF / NOMINAL_FREQ) or > - (LOWEST_PERF / LOWEST_FREQ) > and for cppc_cpufreq_perf_to_khz(): > - (NOMINAL_FREQ / NOMINAL_PERF) or > - ((NOMINAL_PERF - LOWEST_FREQ) / (NOMINAL_PERF - LOWEST_PERF)) > > This means: > 1- the functions are not inverse for some values: > (perf_to_khz(khz_to_perf(x)) != x) > 2- cppc_cpufreq_perf_to_khz(LOWEST_PERF) can sometimes give > a different value from LOWEST_FREQ due to integer approximation > 3- it is implied that performance and frequency are proportional > (NOMINAL_FREQ / NOMINAL_PERF) == (LOWEST_PERF / LOWEST_FREQ) > > This patch changes the conversion functions to an affine function. > This fixes the 3 points above. > > Suggested-by: Lukasz Luba <lukasz.luba@arm.com> > Suggested-by: Morten Rasmussen <morten.rasmussen@arm.com> > Signed-off-by: Pierre Gondois <Pierre.Gondois@arm.com> > --- > drivers/cpufreq/cppc_cpufreq.c | 43 +++++++++++++++++----------------- > 1 file changed, 21 insertions(+), 22 deletions(-) > > diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c > index db17196266e4..5024d9af2e6e 100644 > --- a/drivers/cpufreq/cppc_cpufreq.c > +++ b/drivers/cpufreq/cppc_cpufreq.c > @@ -303,52 +303,48 @@ static u64 cppc_get_dmi_max_khz(void) > > /* > * If CPPC lowest_freq and nominal_freq registers are exposed then we can > - * use them to convert perf to freq and vice versa > - * > - * If the perf/freq point lies between Nominal and Lowest, we can treat > - * (Low perf, Low freq) and (Nom Perf, Nom freq) as 2D co-ordinates of a line > - * and extrapolate the rest > - * For perf/freq > Nominal, we use the ratio perf:freq at Nominal for conversion > + * use them to convert perf to freq and vice versa. The conversion is > + * extrapolated as an affine function passing by the 2 points: > + * - (Low perf, Low freq) > + * - (Nominal perf, Nominal perf) > */ > static unsigned int cppc_cpufreq_perf_to_khz(struct cppc_cpudata *cpu_data, > unsigned int perf) > { > struct cppc_perf_caps *caps = &cpu_data->perf_caps; > + s64 retval, offset = 0; > static u64 max_khz; > u64 mul, div; > > if (caps->lowest_freq && caps->nominal_freq) { > - if (perf >= caps->nominal_perf) { > - mul = caps->nominal_freq; > - div = caps->nominal_perf; > - } else { > - mul = caps->nominal_freq - caps->lowest_freq; > - div = caps->nominal_perf - caps->lowest_perf; > - } > + mul = caps->nominal_freq - caps->lowest_freq; > + div = caps->nominal_perf - caps->lowest_perf; > + offset = caps->nominal_freq - (u64)caps->nominal_perf * mul / div; Since mult is a u64, the other operands need not be cast to u64 explicitly AFAICS. Moreover, it might be better to use div64_u64() instead of the plain integer division. > } else { > if (!max_khz) > max_khz = cppc_get_dmi_max_khz(); > mul = max_khz; > div = caps->highest_perf; > } > - return (u64)perf * mul / div; > + > + retval = offset + (u64)perf * mul / div; > + if (retval >= 0) > + return retval; > + return 0; > } > > static unsigned int cppc_cpufreq_khz_to_perf(struct cppc_cpudata *cpu_data, > unsigned int freq) > { > struct cppc_perf_caps *caps = &cpu_data->perf_caps; > + s64 retval, offset = 0; > static u64 max_khz; > u64 mul, div; > > if (caps->lowest_freq && caps->nominal_freq) { > - if (freq >= caps->nominal_freq) { > - mul = caps->nominal_perf; > - div = caps->nominal_freq; > - } else { > - mul = caps->lowest_perf; > - div = caps->lowest_freq; > - } > + mul = caps->nominal_perf - caps->lowest_perf; > + div = caps->nominal_freq - caps->lowest_freq; > + offset = caps->nominal_perf - (u64)caps->nominal_freq * mul / div; > } else { > if (!max_khz) > max_khz = cppc_get_dmi_max_khz(); > @@ -356,7 +352,10 @@ static unsigned int cppc_cpufreq_khz_to_perf(struct cppc_cpudata *cpu_data, > div = max_khz; > } > > - return (u64)freq * mul / div; > + retval = offset + (u64)freq * mul / div; > + if (retval >= 0) > + return retval; > + return 0; > } > > static int cppc_cpufreq_set_target(struct cpufreq_policy *policy, > -- > 2.25.1 >
diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c index db17196266e4..5024d9af2e6e 100644 --- a/drivers/cpufreq/cppc_cpufreq.c +++ b/drivers/cpufreq/cppc_cpufreq.c @@ -303,52 +303,48 @@ static u64 cppc_get_dmi_max_khz(void) /* * If CPPC lowest_freq and nominal_freq registers are exposed then we can - * use them to convert perf to freq and vice versa - * - * If the perf/freq point lies between Nominal and Lowest, we can treat - * (Low perf, Low freq) and (Nom Perf, Nom freq) as 2D co-ordinates of a line - * and extrapolate the rest - * For perf/freq > Nominal, we use the ratio perf:freq at Nominal for conversion + * use them to convert perf to freq and vice versa. The conversion is + * extrapolated as an affine function passing by the 2 points: + * - (Low perf, Low freq) + * - (Nominal perf, Nominal perf) */ static unsigned int cppc_cpufreq_perf_to_khz(struct cppc_cpudata *cpu_data, unsigned int perf) { struct cppc_perf_caps *caps = &cpu_data->perf_caps; + s64 retval, offset = 0; static u64 max_khz; u64 mul, div; if (caps->lowest_freq && caps->nominal_freq) { - if (perf >= caps->nominal_perf) { - mul = caps->nominal_freq; - div = caps->nominal_perf; - } else { - mul = caps->nominal_freq - caps->lowest_freq; - div = caps->nominal_perf - caps->lowest_perf; - } + mul = caps->nominal_freq - caps->lowest_freq; + div = caps->nominal_perf - caps->lowest_perf; + offset = caps->nominal_freq - (u64)caps->nominal_perf * mul / div; } else { if (!max_khz) max_khz = cppc_get_dmi_max_khz(); mul = max_khz; div = caps->highest_perf; } - return (u64)perf * mul / div; + + retval = offset + (u64)perf * mul / div; + if (retval >= 0) + return retval; + return 0; } static unsigned int cppc_cpufreq_khz_to_perf(struct cppc_cpudata *cpu_data, unsigned int freq) { struct cppc_perf_caps *caps = &cpu_data->perf_caps; + s64 retval, offset = 0; static u64 max_khz; u64 mul, div; if (caps->lowest_freq && caps->nominal_freq) { - if (freq >= caps->nominal_freq) { - mul = caps->nominal_perf; - div = caps->nominal_freq; - } else { - mul = caps->lowest_perf; - div = caps->lowest_freq; - } + mul = caps->nominal_perf - caps->lowest_perf; + div = caps->nominal_freq - caps->lowest_freq; + offset = caps->nominal_perf - (u64)caps->nominal_freq * mul / div; } else { if (!max_khz) max_khz = cppc_get_dmi_max_khz(); @@ -356,7 +352,10 @@ static unsigned int cppc_cpufreq_khz_to_perf(struct cppc_cpudata *cpu_data, div = max_khz; } - return (u64)freq * mul / div; + retval = offset + (u64)freq * mul / div; + if (retval >= 0) + return retval; + return 0; } static int cppc_cpufreq_set_target(struct cpufreq_policy *policy,
CPUfreq governors request CPU frequencies using information on current CPU usage. The CPPC driver converts them to performance requests. Frequency targets are computed as: target_freq = (util / cpu_capacity) * max_freq target_freq is then clamped between [policy->min, policy->max]. The CPPC driver converts performance values to frequencies (and vice-versa) using cppc_cpufreq_perf_to_khz() and cppc_cpufreq_khz_to_perf(). These functions both use two different factors depending on the range of the input value. For cppc_cpufreq_khz_to_perf(): - (NOMINAL_PERF / NOMINAL_FREQ) or - (LOWEST_PERF / LOWEST_FREQ) and for cppc_cpufreq_perf_to_khz(): - (NOMINAL_FREQ / NOMINAL_PERF) or - ((NOMINAL_PERF - LOWEST_FREQ) / (NOMINAL_PERF - LOWEST_PERF)) This means: 1- the functions are not inverse for some values: (perf_to_khz(khz_to_perf(x)) != x) 2- cppc_cpufreq_perf_to_khz(LOWEST_PERF) can sometimes give a different value from LOWEST_FREQ due to integer approximation 3- it is implied that performance and frequency are proportional (NOMINAL_FREQ / NOMINAL_PERF) == (LOWEST_PERF / LOWEST_FREQ) This patch changes the conversion functions to an affine function. This fixes the 3 points above. Suggested-by: Lukasz Luba <lukasz.luba@arm.com> Suggested-by: Morten Rasmussen <morten.rasmussen@arm.com> Signed-off-by: Pierre Gondois <Pierre.Gondois@arm.com> --- drivers/cpufreq/cppc_cpufreq.c | 43 +++++++++++++++++----------------- 1 file changed, 21 insertions(+), 22 deletions(-)