Re: [PATCH v3 15/15] xen/cpufreq: Adapt SET/GET_CPUFREQ_CPPC xen_sysctl_pm_op for amd-cppc driver

[Jan Beulich <jbeulich@xxxxxxxx>]

On 06.03.2025 09:39, Penny Zheng wrote:
> Introduce helper set_amd_cppc_para and get_amd_cppc_para to
> SET/GET CPPC-related para for amd-cppc/amd-cppc-epp driver.
> 
> Signed-off-by: Penny Zheng <Penny.Zheng@xxxxxxx>
> ---
> v1 -> v2:
> - Give the variable des_perf an initializer of 0
> - Use the strncmp()s directly in the if()
> ---
>  xen/arch/x86/acpi/cpufreq/amd-cppc.c | 124 +++++++++++++++++++++++++++
>  xen/drivers/acpi/pmstat.c            |  20 ++++-
>  xen/include/acpi/cpufreq/cpufreq.h   |   5 ++
>  3 files changed, 145 insertions(+), 4 deletions(-)
> 
> diff --git a/xen/arch/x86/acpi/cpufreq/amd-cppc.c 
> b/xen/arch/x86/acpi/cpufreq/amd-cppc.c
> index 606bb648b3..28c13b09c8 100644
> --- a/xen/arch/x86/acpi/cpufreq/amd-cppc.c
> +++ b/xen/arch/x86/acpi/cpufreq/amd-cppc.c
> @@ -32,6 +32,7 @@
>  
>  static bool __ro_after_init opt_active_mode;
>  static DEFINE_PER_CPU_READ_MOSTLY(uint8_t, epp_init);
> +static bool __ro_after_init amd_cppc_in_use;
>  
>  struct amd_cppc_drv_data
>  {
> @@ -513,6 +514,123 @@ static int cf_check amd_cppc_epp_set_policy(struct 
> cpufreq_policy *policy)
>      return amd_cppc_epp_update_limit(policy);
>  }
>  
> +int get_amd_cppc_para(unsigned int cpu,
> +                      struct xen_cppc_para *cppc_para)
> +{
> +    const struct amd_cppc_drv_data *data = per_cpu(amd_cppc_drv_data, cpu);
> +
> +    if ( data == NULL )
> +        return -ENODATA;
> +
> +    cppc_para->features         = 0;
> +    cppc_para->lowest           = data->caps.lowest_perf;
> +    cppc_para->lowest_nonlinear = data->caps.lowest_nonlinear_perf;
> +    cppc_para->nominal          = data->caps.nominal_perf;
> +    cppc_para->highest          = data->caps.highest_perf;
> +    cppc_para->minimum          = data->req.min_perf;
> +    cppc_para->maximum          = data->req.max_perf;
> +    cppc_para->desired          = data->req.des_perf;
> +    cppc_para->energy_perf      = data->req.epp;
> +
> +    return 0;
> +}
> +
> +int set_amd_cppc_para(const struct cpufreq_policy *policy,
> +                      const struct xen_set_cppc_para *set_cppc)
> +{
> +    unsigned int cpu = policy->cpu;
> +    struct amd_cppc_drv_data *data = per_cpu(amd_cppc_drv_data, cpu);
> +    uint8_t max_perf, min_perf, des_perf = 0, epp;
> +
> +    if ( data == NULL )
> +        return -ENOENT;
> +
> +    /* Validate all parameters - Disallow reserved bits. */
> +    if ( set_cppc->minimum > UINT8_MAX || set_cppc->maximum > UINT8_MAX ||
> +         set_cppc->desired > UINT8_MAX || set_cppc->energy_perf > UINT8_MAX )
> +        return -EINVAL;
> +
> +    /* Only allow values if params bit is set. */
> +    if ( (!(set_cppc->set_params & XEN_SYSCTL_CPPC_SET_DESIRED) &&
> +          set_cppc->desired) ||
> +         (!(set_cppc->set_params & XEN_SYSCTL_CPPC_SET_MINIMUM) &&
> +          set_cppc->minimum) ||
> +         (!(set_cppc->set_params & XEN_SYSCTL_CPPC_SET_MAXIMUM) &&
> +          set_cppc->maximum) ||
> +         (!(set_cppc->set_params & XEN_SYSCTL_CPPC_SET_ENERGY_PERF) &&
> +          set_cppc->energy_perf) )
> +        return -EINVAL;
> +
> +    /* Activity window not supported in MSR */
> +    if ( set_cppc->set_params & XEN_SYSCTL_CPPC_SET_ACT_WINDOW )
> +        return -EOPNOTSUPP;
> +
> +    /* Return if there is nothing to do. */
> +    if ( set_cppc->set_params == 0 )
> +        return 0;
> +
> +    epp = per_cpu(epp_init, cpu);
> +    /* Apply presets */
> +    /*
> +     * XEN_SYSCTL_CPPC_SET_PRESET_POWERSAVE/PERFORMANCE/BALANCE are
> +     * for amd-cppc in active mode, min_perf could be set with lowest_perf
> +     * representing the T-state range of performance levels, while
> +     * XEN_SYSCTL_CPPC_SET_PRESET_NONE is for amd-cppc in passive mode, it
> +     * depends on governor to do performance scaling, setting with
> +     * lowest_nonlinear_perf to ensures performance in P-state range.
> +     */

Nit: There are again two consecutive comments here.

The active / passive mode distinction mentioned in the comment isn't
reflected anywhere in the code. It's the XEN_SYSCTL_CPPC_SET_DESIRED
which distinguishes them, yet that flag isn't mentioned in the comment.

> +    switch ( set_cppc->set_params & XEN_SYSCTL_CPPC_SET_PRESET_MASK )
> +    {
> +    case XEN_SYSCTL_CPPC_SET_PRESET_POWERSAVE:
> +        if ( set_cppc->set_params & XEN_SYSCTL_CPPC_SET_DESIRED )
> +            return -EINVAL;
> +        min_perf = data->caps.lowest_perf;
> +        max_perf = data->caps.highest_perf;

These are still not not both ".lowest_perf", and I still don't understand
- due to the lack of a comment - why that is.

> +        epp = CPPC_ENERGY_PERF_MAX_POWERSAVE;
> +        break;
> +
> +    case XEN_SYSCTL_CPPC_SET_PRESET_PERFORMANCE:
> +        if ( set_cppc->set_params & XEN_SYSCTL_CPPC_SET_DESIRED )
> +            return -EINVAL;
> +        min_perf = data->caps.highest_perf;
> +        max_perf = data->caps.highest_perf;
> +        epp = CPPC_ENERGY_PERF_MAX_PERFORMANCE;
> +        break;
> +
> +    case XEN_SYSCTL_CPPC_SET_PRESET_BALANCE:
> +        if ( set_cppc->set_params & XEN_SYSCTL_CPPC_SET_DESIRED )
> +            return -EINVAL;
> +        min_perf = data->caps.lowest_perf;
> +        max_perf = data->caps.highest_perf;
> +        epp = CPPC_ENERGY_PERF_BALANCE;
> +        break;
> +
> +    case XEN_SYSCTL_CPPC_SET_PRESET_NONE:
> +        min_perf = data->caps.lowest_nonlinear_perf;
> +        max_perf = data->caps.highest_perf;
> +        break;
> +
> +    default:
> +        return -EINVAL;
> +    }
> +
> +    /* Further customize presets if needed */
> +    if ( set_cppc->set_params & XEN_SYSCTL_CPPC_SET_MINIMUM )
> +        min_perf = set_cppc->minimum;
> +
> +    if ( set_cppc->set_params & XEN_SYSCTL_CPPC_SET_MAXIMUM )
> +        max_perf = set_cppc->maximum;
> +
> +    if ( set_cppc->set_params & XEN_SYSCTL_CPPC_SET_ENERGY_PERF )
> +        epp = set_cppc->energy_perf;
> +
> +    if ( set_cppc->set_params & XEN_SYSCTL_CPPC_SET_DESIRED )
> +        des_perf = set_cppc->desired;

Considering these I even less understand what the comment further up is
about.

> +    return amd_cppc_write_request(cpu, min_perf, des_perf, max_perf, epp);
> +}
> +
> +

Nit (not for the first time, I think): No double blank lines please.

> @@ -533,6 +651,11 @@ amd_cppc_epp_driver =
>      .exit       = amd_cppc_cpufreq_cpu_exit,
>  };
>  
> +bool amd_cppc_active(void)
> +{
> +    return amd_cppc_in_use;
> +}
> +
>  int __init amd_cppc_register_driver(void)
>  {
>      int ret;
> @@ -552,6 +675,7 @@ int __init amd_cppc_register_driver(void)
>  
>      /* Remove possible fallback option */
>      xen_processor_pmbits &= ~XEN_PROCESSOR_PM_PX;
> +    amd_cppc_in_use = true;

Is this separate flag really needed? Can't you go from xen_processor_pmbits?

> --- a/xen/drivers/acpi/pmstat.c
> +++ b/xen/drivers/acpi/pmstat.c
> @@ -261,7 +261,16 @@ static int get_cpufreq_para(struct xen_sysctl_pm_op *op)
>           !strncmp(op->u.get_para.scaling_driver, XEN_HWP_DRIVER_NAME,
>                    CPUFREQ_NAME_LEN) )
>          ret = get_hwp_para(policy->cpu, &op->u.get_para.u.cppc_para);
> -    else
> +    else if ( !strncmp(op->u.get_para.scaling_driver, 
> XEN_AMD_CPPC_DRIVER_NAME,
> +                       CPUFREQ_NAME_LEN) ||
> +              !strncmp(op->u.get_para.scaling_driver, 
> XEN_AMD_CPPC_EPP_DRIVER_NAME,

Overlong line again.

Jan