This is a note to let you know that I've just added the patch titled
cpufreq: CPPC: Fix performance/frequency conversion
to the 5.16-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
cpufreq-cppc-fix-performance-frequency-conversion.patch
and it can be found in the queue-5.16 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 7526e71b68e2f761d50c9945567af236d0d4baa0
Author: Pierre Gondois <Pierre.Gondois@xxxxxxx>
Date: Tue Feb 8 09:01:09 2022 +0100
cpufreq: CPPC: Fix performance/frequency conversion
[ Upstream commit ec1c7ad47664f964c1101fe555b6fde0cb124b38 ]
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@xxxxxxx>
Suggested-by: Morten Rasmussen <morten.rasmussen@xxxxxxx>
Signed-off-by: Pierre Gondois <Pierre.Gondois@xxxxxxx>
Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
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,
