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authorPierre Gondois2022-02-08 09:01:09 +0100
committerViresh Kumar2022-02-10 10:56:52 +0530
commitec1c7ad47664f964c1101fe555b6fde0cb124b38 (patch)
treee2c74b6ebff3212fc0470eaf055f22e087bd2786 /drivers
parentbc8b0c271bbf1e1a303087eb4b393cc0b791fc9d (diff)
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.c43
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,