Re: [PATCH v3 2/2] cpufreq: CPPC: add autonomous mode boot parameter support

[Sumit Gupta <sumitg@nvidia.com>]

Hi Mario,


On 16/05/26 02:43, Mario Limonciello wrote:
> External email: Use caution opening links or attachments
>
>
> On 5/15/26 07:26, Sumit Gupta wrote:
>> Add a kernel boot parameter 'cppc_cpufreq.auto_sel_mode' to enable
>> CPPC autonomous performance selection on all CPUs at system startup.
>> When autonomous mode is enabled, the hardware automatically adjusts
>> CPU performance based on workload demands using Energy Performance
>> Preference (EPP) hints.
>>
>> When the parameter is set:
>> - Configure all CPUs for autonomous operation on first init
>> - Use HW min/max_perf when available; otherwise initialize from caps
>> - Initialize desired_perf to max_perf as a starting hint
>> - Hardware controls frequency instead of the OS governor
>> - EPP behavior depends on parameter value:
>>    - performance (or 1): override EPP to performance preference (0x0)
>>    - default_epp (or 2): preserve EPP value programmed by BIOS/firmware
>>
>> The boot parameter is applied only during first policy initialization.
>> Skip applying it on CPU hotplug to preserve runtime sysfs configuration.
>>
>> This patch depends on patch series [1] ("cpufreq: Set policy->min and
>> max as real QoS constraints") so that the policy->min/max set in
>> cppc_cpufreq_cpu_init() are not overridden by cpufreq_set_policy()
>> during init.
>>
>> Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
>> ---
>> [1] 
>> https://lore.kernel.org/lkml/20260511135538.522653-1-pierre.gondois@arm.com/
>> ---
>>   .../admin-guide/kernel-parameters.txt         |  16 +++
>>   drivers/cpufreq/cppc_cpufreq.c                | 122 +++++++++++++++++-
>>   2 files changed, 133 insertions(+), 5 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt 
>> b/Documentation/admin-guide/kernel-parameters.txt
>> index 0eb64aab3685..7e4b3a8fd76f 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -1048,6 +1048,22 @@ Kernel parameters
>>                       policy to use. This governor must be registered 
>> in the
>>                       kernel before the cpufreq driver probes.
>>
>> +     cppc_cpufreq.auto_sel_mode=
>> +                     [CPU_FREQ] Enable ACPI CPPC autonomous performance
>> +                     selection. When enabled, hardware automatically 
>> adjusts
>> +                     CPU frequency on all CPUs based on workload 
>> demands.
>> +                     In Autonomous mode, Energy Performance 
>> Preference (EPP)
>> +                     hints guide hardware toward performance (0x0) 
>> or energy
>> +                     efficiency (0xff).
>> +                     Requires ACPI CPPC autonomous selection register
>> +                     support.
>> +                     Accepts:
>> +                       performance, 1: enable auto_sel + set EPP to
>> +                                       performance (0x0)
>> +                       default_epp, 2: enable auto_sel, preserve EPP 
>> value
>> +                                       programmed by BIOS/firmware
>> +                     Unset: cpufreq governors are used (auto_sel 
>> disabled).
>
> Rather than unset doing nothing, have you considered having it take a
> midpoint like 128?  That's what we do in amd-pstate (default to
> balance_performance).  I think it turns into a reasonable balance. 

Thanks for the suggestion.
I can add balance_performance that enables auto_sel with EPP=128 in v4.

On changing the driver default (no param behavior) to auto enable
balance_performance, it would be good to keep the current behavior for
now since cppc_cpufreq is generic across ARM64/RISC-V platforms where
EPP and Autonomous Selection registers are optional.
A default change would affect existing users relying on governors.

Thank you,
Sumit Gupta


>
>> +
>>       cpu_init_udelay=N
>>                       [X86,EARLY] Delay for N microsec between assert 
>> and de-assert
>>                       of APIC INIT to start processors.  This delay 
>> occurs
>> diff --git a/drivers/cpufreq/cppc_cpufreq.c 
>> b/drivers/cpufreq/cppc_cpufreq.c
>> index 6b54427b52e1..5f4d735e7c7d 100644
>> --- a/drivers/cpufreq/cppc_cpufreq.c
>> +++ b/drivers/cpufreq/cppc_cpufreq.c
>> @@ -28,6 +28,43 @@
>>
>>   static struct cpufreq_driver cppc_cpufreq_driver;
>>
>> +/* Autonomous Selection boot parameter modes */
>> +enum {
>> +     AUTO_SEL_PERFORMANCE = 1,
>> +     AUTO_SEL_DEFAULT_EPP = 2,
>> +};
>> +
>> +static int auto_sel_mode;
>> +
>> +static int auto_sel_mode_set(const char *val, const struct 
>> kernel_param *kp)
>> +{
>> +     if (sysfs_streq(val, "performance") || sysfs_streq(val, "1"))
>> +             *(int *)kp->arg = AUTO_SEL_PERFORMANCE;
>> +     else if (sysfs_streq(val, "default_epp") || sysfs_streq(val, "2"))
>> +             *(int *)kp->arg = AUTO_SEL_DEFAULT_EPP;
>> +     else
>> +             return -EINVAL;
>> +
>> +     return 0;
>> +}
>> +
>> +static int auto_sel_mode_get(char *buffer, const struct kernel_param 
>> *kp)
>> +{
>> +     switch (*(int *)kp->arg) {
>> +     case AUTO_SEL_PERFORMANCE:
>> +             return sysfs_emit(buffer, "performance\n");
>> +     case AUTO_SEL_DEFAULT_EPP:
>> +             return sysfs_emit(buffer, "default_epp\n");
>> +     default:
>> +             return sysfs_emit(buffer, "disabled\n");
>> +     }
>> +}
>> +
>> +static const struct kernel_param_ops auto_sel_mode_ops = {
>> +     .set = auto_sel_mode_set,
>> +     .get = auto_sel_mode_get,
>> +};
>> +
>>   #ifdef CONFIG_ACPI_CPPC_CPUFREQ_FIE
>>   static enum {
>>       FIE_UNSET = -1,
>> @@ -715,11 +752,75 @@ static int cppc_cpufreq_cpu_init(struct 
>> cpufreq_policy *policy)
>>       policy->cur = cppc_perf_to_khz(caps, caps->highest_perf);
>>       cpu_data->perf_ctrls.desired_perf = caps->highest_perf;
>>
>> -     ret = cppc_set_perf(cpu, &cpu_data->perf_ctrls);
>> -     if (ret) {
>> -             pr_debug("Err setting perf value:%d on CPU:%d. ret:%d\n",
>> -                      caps->highest_perf, cpu, ret);
>> -             goto out;
>> +     /*
>> +      * Enable autonomous mode on first init if boot param is set.
>> +      * Check last_governor to detect first init and skip if auto_sel
>> +      * is already enabled.
>> +      */
>> +     if (auto_sel_mode && policy->last_governor[0] == '\0' &&
>> +         !cpu_data->perf_ctrls.auto_sel) {
>> +             /* Init min/max_perf from caps if not already set by 
>> HW. */
>> +             if (!cpu_data->perf_ctrls.min_perf)
>> +                     cpu_data->perf_ctrls.min_perf = 
>> caps->lowest_nonlinear_perf;
>> +             if (!cpu_data->perf_ctrls.max_perf)
>> +                     cpu_data->perf_ctrls.max_perf = 
>> policy->boost_enabled ?
>> +                             caps->highest_perf : caps->nominal_perf;
>> +
>> +             /*
>> +              * In autonomous mode desired_perf is only a hint; EPP and
>> +              * the platform drive actual selection within [min, max].
>> +              * Initialize it to max_perf so HW starts at the upper 
>> bound.
>> +              */
>> +             cpu_data->perf_ctrls.desired_perf = 
>> cpu_data->perf_ctrls.max_perf;
>> +
>> +             policy->cur = cppc_perf_to_khz(caps,
>> + cpu_data->perf_ctrls.desired_perf);
>> +
>> +             /*
>> +              * Override EPP only in 'performance' mode; 
>> 'default_epp' mode
>> +              * preserves the BIOS/firmware programmed EPP value.
>> +              * EPP is optional - some platforms may not support it.
>> +              */
>> +             if (auto_sel_mode == AUTO_SEL_PERFORMANCE) {
>> +                     ret = cppc_set_epp(cpu, 
>> CPPC_EPP_PERFORMANCE_PREF);
>> +                     if (ret && ret != -EOPNOTSUPP)
>> +                             pr_warn("Failed to set EPP for CPU%d 
>> (%d)\n", cpu, ret);
>> +                     else if (!ret)
>> + cpu_data->perf_ctrls.energy_perf = CPPC_EPP_PERFORMANCE_PREF;
>> +             }
>> +
>> +             /* Program min/max/desired into CPPC regs (non-fatal on 
>> failure). */
>> +             ret = cppc_set_perf(cpu, &cpu_data->perf_ctrls);
>> +             if (ret)
>> +                     pr_warn("set_perf failed CPU%d (%d); using HW 
>> values\n",
>> +                             cpu, ret);
>> +
>> +             ret = cppc_set_auto_sel(cpu, true);
>> +             if (ret && ret != -EOPNOTSUPP)
>> +                     pr_warn("auto_sel CPU%d failed (%d); using OS 
>> mode\n",
>> +                             cpu, ret);
>> +             else if (!ret)
>> +                     cpu_data->perf_ctrls.auto_sel = true;
>> +     }
>> +
>> +     if (cpu_data->perf_ctrls.auto_sel) {
>> +             /* Sync policy limits from HW when autonomous mode is 
>> active */
>> +             policy->min = cppc_perf_to_khz(caps,
>> + cpu_data->perf_ctrls.min_perf ?:
>> + caps->lowest_nonlinear_perf);
>> +             policy->max = cppc_perf_to_khz(caps,
>> + cpu_data->perf_ctrls.max_perf ?:
>> + (policy->boost_enabled ?
>> + caps->highest_perf :
>> + caps->nominal_perf));
>> +     } else {
>> +             /* Normal mode: governors control frequency */
>> +             ret = cppc_set_perf(cpu, &cpu_data->perf_ctrls);
>> +             if (ret) {
>> +                     pr_debug("Err setting perf value:%d on CPU:%d. 
>> ret:%d\n",
>> +                              caps->highest_perf, cpu, ret);
>> +                     goto out;
>> +             }
>>       }
>>
>>       cppc_cpufreq_cpu_fie_init(policy);
>> @@ -1079,10 +1180,21 @@ static int __init cppc_cpufreq_init(void)
>>
>>   static void __exit cppc_cpufreq_exit(void)
>>   {
>> +     unsigned int cpu;
>> +
>> +     for_each_present_cpu(cpu)
>> +             cppc_set_auto_sel(cpu, false);
>> +
>>       cpufreq_unregister_driver(&cppc_cpufreq_driver);
>>       cppc_freq_invariance_exit();
>>   }
>>
>> +module_param_cb(auto_sel_mode, &auto_sel_mode_ops, &auto_sel_mode, 
>> 0444);
>> +MODULE_PARM_DESC(auto_sel_mode,
>> +              "Enable CPPC autonomous performance selection at boot: "
>> +              "performance or 1 (EPP=performance), "
>> +              "default_epp or 2 (preserve BIOS/firmware EPP)");
>> +
>>   module_exit(cppc_cpufreq_exit);
>>   MODULE_AUTHOR("Ashwin Chaugule");
>>   MODULE_DESCRIPTION("CPUFreq driver based on the ACPI CPPC v5.0+ 
>> spec");
>