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author | Pierre Gondois <Pierre.Gondois@arm.com> | 2022-02-08 09:01:09 +0100 |
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committer | Viresh Kumar <viresh.kumar@linaro.org> | 2022-02-10 10:56:52 +0530 |
commit | ec1c7ad47664f964c1101fe555b6fde0cb124b38 (patch) | |
tree | e2c74b6ebff3212fc0470eaf055f22e087bd2786 /drivers | |
parent | bc8b0c271bbf1e1a303087eb4b393cc0b791fc9d (diff) | |
download | linux-ec1c7ad47664f964c1101fe555b6fde0cb124b38.tar.gz linux-ec1c7ad47664f964c1101fe555b6fde0cb124b38.tar.bz2 linux-ec1c7ad47664f964c1101fe555b6fde0cb124b38.zip |
cpufreq: CPPC: Fix performance/frequency conversion
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>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Diffstat (limited to 'drivers')
-rw-r--r-- | drivers/cpufreq/cppc_cpufreq.c | 43 |
1 files changed, 21 insertions, 22 deletions
diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c index db17196266e4..82d370ae6a4a 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 - div64_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 + div64_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 - div64_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 + div64_u64(freq * mul, div); + if (retval >= 0) + return retval; + return 0; } static int cppc_cpufreq_set_target(struct cpufreq_policy *policy, |