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cpufreq: Add special-purpose fast-switching callback for drivers

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First off, some cpufreq drivers (eg. intel_pstate) can pass hints
beyond the current target frequency to the hardware and there are no
provisions for doing that in the cpufreq framework.  In particular,
today the driver has to assume that it should not allow the frequency
to fall below the one requested by the governor (or the required
capacity may not be provided) which may not be the case and which may
lead to excessive energy usage in some scenarios.

Second, the hints passed by these drivers to the hardware need not be
in terms of the frequency, so representing the utilization numbers
coming from the scheduler as frequency before passing them to those
drivers is not really useful.

Address the two points above by adding a special-purpose replacement
for the ->fast_switch callback, called ->adjust_perf, allowing the
governor to pass abstract performance level (rather than frequency)
values for the minimum (required) and target (desired) performance
along with the CPU capacity to compare them to.

Also update the schedutil governor to use the new callback instead
of ->fast_switch if present and if the utilization mertics are
frequency-invariant (that is requisite for the direct mapping
between the utilization and the CPU performance levels to be a
reasonable approximation).

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
This commit is contained in:
Rafael J. Wysocki
2020-12-14 21:08:00 +01:00
parent ca6827de4b
commit ee2cc4276b
4 changed files with 117 additions and 10 deletions
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14
include/linux/cpufreq.h
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@@ -320,6 +320,15 @@ struct cpufreq_driver {
unsigned int index);
unsigned int (*fast_switch)(struct cpufreq_policy *policy,
unsigned int target_freq);
/*
* ->fast_switch() replacement for drivers that use an internal
* representation of performance levels and can pass hints other than
* the target performance level to the hardware.
*/
void (*adjust_perf)(unsigned int cpu,
unsigned long min_perf,
unsigned long target_perf,
unsigned long capacity);
/*
* Caches and returns the lowest driver-supported frequency greater than
@@ -588,6 +597,11 @@ struct cpufreq_governor {
/* Pass a target to the cpufreq driver */
unsigned int cpufreq_driver_fast_switch(struct cpufreq_policy *policy,
unsigned int target_freq);
void cpufreq_driver_adjust_perf(unsigned int cpu,
unsigned long min_perf,
unsigned long target_perf,
unsigned long capacity);
bool cpufreq_driver_has_adjust_perf(void);
int cpufreq_driver_target(struct cpufreq_policy *policy,
unsigned int target_freq,
unsigned int relation);