Re: [PATCH v2] cpufreq: intel_pstate: Adjust the .adjust_perf() driver callback

[Zhongqiu Han <zhongqiu.han@oss.qualcomm.com>]

On 6/19/2026 10:52 PM, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> In some cases, the processor may not actually stick to the "desired"
> performance level programmed through the driver's .adjust_perf()
> callback and may go above it, which may not be desirable (for instance,
> there may be a UCLAMP_MAX limit set for the task currently running on
> the given CPU which should be respected).
> 
> Address that by adjusting the .adjust_perf() callback to take an
> additional argument, max_perf, representing the maximum allowed
> performance level of the CPU and update the intel_pstate driver to
> take that argument into account as appropriate.
> 
> Accordingly, adjust cpufreq_driver_adjust_perf() and the other existing
> user of .adjust_perf(), which is the amd-pstate driver (but the behavior
> of that driver is not changed).
> 
> While at it, also update the cpufreq_driver_adjust_perf()
> documentation to reflect this change and some previous code
> changes that have not been taken into account in it.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Acked-by: Viresh Kumar <viresh.kumar@linaro.org>

Looks good to me. Thanks

Reviewed-by: Zhongqiu Han <zhongqiu.han@oss.qualcomm.com>

> ---
> 
> This is an update of
> 
> https://lore.kernel.org/linux-pm/14060154.uLZWGnKmhe@rafael.j.wysocki/
> 
> sent mainly because the v1 did not update the Rust bindings by
> omission.  It also fixes a few typos present in the v1.
> 
> Thanks!
> 
> ---
>   drivers/cpufreq/amd-pstate.c     |    1 +
>   drivers/cpufreq/cpufreq.c        |   14 +++++++++-----
>   drivers/cpufreq/intel_pstate.c   |    9 ++++++++-
>   include/linux/cpufreq.h          |    2 ++
>   kernel/sched/cpufreq_schedutil.c |    4 +++-
>   rust/kernel/cpufreq.rs           |    6 ++++--
>   6 files changed, 27 insertions(+), 9 deletions(-)
> 
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -781,6 +781,7 @@ static unsigned int amd_pstate_fast_swit
>   static void amd_pstate_adjust_perf(struct cpufreq_policy *policy,
>   				   unsigned long _min_perf,
>   				   unsigned long target_perf,
> +				   unsigned long _max_perf,
>   				   unsigned long capacity)
>   {
>   	u8 max_perf, min_perf, des_perf, cap_perf;
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -2252,14 +2252,17 @@ EXPORT_SYMBOL_GPL(cpufreq_driver_fast_sw
>    * @policy: cpufreq policy object of the target CPU.
>    * @min_perf: Minimum (required) performance level (units of @capacity).
>    * @target_perf: Target (desired) performance level (units of @capacity).
> + * @max_perf: Maximum (allowed) performance level (units of @capacity).
>    * @capacity: Capacity of the target CPU.
>    *
> - * Carry out a fast performance level switch of @cpu without sleeping.
> + * Carry out a fast performance level adjustment for the CPU represented by
> + * @policy without sleeping.
>    *
>    * The driver's ->adjust_perf() callback invoked by this function must be
> - * suitable for being called from within RCU-sched read-side critical sections
> - * and it is expected to select a suitable performance level equal to or above
> - * @min_perf and preferably equal to or below @target_perf.
> + * suitable for calling from within RCU-sched read-side critical sections and
> + * it is expected to program the processor to select suitable performance
> + * levels between @min_perf and @max_perf inclusive and preferably close to
> + * @target_perf going forward for the CPU represented by @policy.
>    *
>    * This function must not be called if policy->fast_switch_enabled is unset.
>    *
> @@ -2271,9 +2274,10 @@ EXPORT_SYMBOL_GPL(cpufreq_driver_fast_sw
>   void cpufreq_driver_adjust_perf(struct cpufreq_policy *policy,
>   				 unsigned long min_perf,
>   				 unsigned long target_perf,
> +				 unsigned long max_perf,
>   				 unsigned long capacity)
>   {
> -	cpufreq_driver->adjust_perf(policy, min_perf, target_perf, capacity);
> +	cpufreq_driver->adjust_perf(policy, min_perf, target_perf, max_perf, capacity);
>   }
>   
>   /**
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -3241,6 +3241,7 @@ static unsigned int intel_cpufreq_fast_s
>   static void intel_cpufreq_adjust_perf(struct cpufreq_policy *policy,
>   				      unsigned long min_perf,
>   				      unsigned long target_perf,
> +				      unsigned long max_perf,
>   				      unsigned long capacity)
>   {
>   	struct cpudata *cpu = all_cpu_data[policy->cpu];
> @@ -3271,7 +3272,13 @@ static void intel_cpufreq_adjust_perf(st
>   	if (min_pstate > cpu->max_perf_ratio)
>   		min_pstate = cpu->max_perf_ratio;
>   
> -	max_pstate = min(cap_pstate, cpu->max_perf_ratio);
> +	max_pstate = cap_pstate;
> +	if (max_perf < capacity)
> +		max_pstate = DIV_ROUND_UP(cap_pstate * max_perf, capacity);
> +
> +	if (max_pstate > cpu->max_perf_ratio)
> +		max_pstate = cpu->max_perf_ratio;
> +
>   	if (max_pstate < min_pstate)
>   		max_pstate = min_pstate;
>   
> --- a/include/linux/cpufreq.h
> +++ b/include/linux/cpufreq.h
> @@ -379,6 +379,7 @@ struct cpufreq_driver {
>   	void		(*adjust_perf)(struct cpufreq_policy *policy,
>   				       unsigned long min_perf,
>   				       unsigned long target_perf,
> +				       unsigned long max_perf,
>   				       unsigned long capacity);
>   
>   	/*
> @@ -624,6 +625,7 @@ unsigned int cpufreq_driver_fast_switch(
>   void cpufreq_driver_adjust_perf(struct cpufreq_policy *policy,
>   				unsigned long min_perf,
>   				unsigned long target_perf,
> +				unsigned long max_perf,
>   				unsigned long capacity);
>   bool cpufreq_driver_has_adjust_perf(void);
>   int cpufreq_driver_target(struct cpufreq_policy *policy,
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -50,6 +50,7 @@ struct sugov_cpu {
>   
>   	unsigned long		util;
>   	unsigned long		bw_min;
> +	unsigned long		bw_max;
>   
>   	/* The field below is for single-CPU policies only: */
>   #ifdef CONFIG_NO_HZ_COMMON
> @@ -232,6 +233,7 @@ static void sugov_get_util(struct sugov_
>   	util = effective_cpu_util(sg_cpu->cpu, util, &min, &max);
>   	util = max(util, boost);
>   	sg_cpu->bw_min = min;
> +	sg_cpu->bw_max = max;
>   	sg_cpu->util = sugov_effective_cpu_perf(sg_cpu->cpu, util, min, max);
>   }
>   
> @@ -484,7 +486,7 @@ static void sugov_update_single_perf(str
>   		sg_cpu->util = prev_util;
>   
>   	cpufreq_driver_adjust_perf(sg_policy->policy, sg_cpu->bw_min,
> -				   sg_cpu->util, max_cap);
> +				   sg_cpu->util, sg_cpu->bw_max, max_cap);
>   
>   	sg_policy->last_freq_update_time = time;
>   }
> --- a/rust/kernel/cpufreq.rs
> +++ b/rust/kernel/cpufreq.rs
> @@ -792,7 +792,8 @@ pub trait Driver {
>       }
>   
>       /// Driver's `adjust_perf` callback.
> -    fn adjust_perf(_policy: &mut Policy, _min_perf: usize, _target_perf: usize, _capacity: usize) {
> +    fn adjust_perf(_policy: &mut Policy, _min_perf: usize, _target_perf: usize,
> +                   _max_perf: usize, _capacity: usize) {
>           build_error!(VTABLE_DEFAULT_ERROR)
>       }
>   
> @@ -1262,12 +1263,13 @@ impl<T: Driver> Registration<T> {
>           ptr: *mut bindings::cpufreq_policy,
>           min_perf: c_ulong,
>           target_perf: c_ulong,
> +        max_perf: c_ulong,
>           capacity: c_ulong,
>       ) {
>           // SAFETY: The `ptr` is guaranteed to be valid by the contract with the C code for the
>           // lifetime of `policy`.
>           let policy = unsafe { Policy::from_raw_mut(ptr) };
> -        T::adjust_perf(policy, min_perf, target_perf, capacity);
> +        T::adjust_perf(policy, min_perf, target_perf, max_perf, capacity);
>       }
>   
>       /// Driver's `get_intermediate` callback.
> 
> 
> 


-- 
Thx and BRs,
Zhongqiu Han