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

[Sumit Gupta <sumitg@nvidia.com>]

On 18/05/26 19:20, Mario Limonciello wrote:
> External email: Use caution opening links or attachments
>
>
> On 5/18/26 08:44, Sumit Gupta wrote:
>> 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
>
> But couldn't you make the "no module parameter set" follow the behavior
> to only set the registers if they're available?
>
> So the systems that support it start using it, the ones that don't it's
> a NOP.
>

Would it work to add balance_performance as a new mode in v4,
and discuss changing the default separately as a follow-up?

Runtime detection helps for unsupported platforms. But platforms which
support the registers use OS governors today, and silently switching
them to autonomous mode on a kernel update is a behavior change for
existing users. They would also have no way to boot into sw governor.

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");
>>>
>