Re: [PATCH v4 17/19] cpufreq/amd-pstate: Rework CPPC enabling

Mario Limonciello
2025-02-25T02:35:17Z

>> + /* Enable autonomous mode for EPP */
>> + if (cppc_state == AMD_PSTATE_ACTIVE) {
>> + /* Set desired perf as zero to allow EPP firmware control */
>> + perf_ctrls.desired_perf = 0;
>> + ret = cppc_set_perf(policy->cpu, &perf_ctrls);
>
> I'm thinking do we need this "setting of desired_perf" as a part of shmem_cppc_enable,
> one thing is we're not doing it in the "msr_" counterpart
> also, I guess this would be taken care as part of amd_pstate_epp_set_policy()->amd_pstate_epp_update_limit()->amd_pstate_update_perf()

Great point, agreed will drop it.

>
>> }
>>
>> - cppc_enabled = enable;
>> return ret;
>> }
>>
>> DEFINE_STATIC_CALL(amd_pstate_cppc_enable, msr_cppc_enable);
>>
>> -static inline int amd_pstate_cppc_enable(bool enable)
>> +static inline int amd_pstate_cppc_enable(struct cpufreq_policy *policy)
>> {
>> - return static_call(amd_pstate_cppc_enable)(enable);
>> + return static_call(amd_pstate_cppc_enable)(policy);
>> }
>>
>> static int msr_init_perf(struct amd_cpudata *cpudata)
>> @@ -1115,28 +1060,6 @@ static void amd_pstate_cpu_exit(struct cpufreq_policy *policy)
>> kfree(cpudata);
>> }
>>
>> -static int amd_pstate_cpu_resume(struct cpufreq_policy *policy)
>> -{
>> - int ret;
>> -
>> - ret = amd_pstate_cppc_enable(true);
>> - if (ret)
>> - pr_err("failed to enable amd-pstate during resume, return %d\n", ret);
>> -
>> - return ret;
>> -}
>> -
>> -static int amd_pstate_cpu_suspend(struct cpufreq_policy *policy)
>> -{
>> - int ret;
>> -
>> - ret = amd_pstate_cppc_enable(false);
>> - if (ret)
>> - pr_err("failed to disable amd-pstate during suspend, return %d\n", ret);
>> -
>> - return ret;
>> -}
>> -
>> /* Sysfs attributes */
>>
>> /*
>> @@ -1228,8 +1151,10 @@ static ssize_t show_energy_performance_available_preferences(
>> static ssize_t store_energy_performance_preference(
>> struct cpufreq_policy *policy, const char *buf, size_t count)
>> {
>> + struct amd_cpudata *cpudata = policy->driver_data;
>> char str_preference[21];
>> ssize_t ret;
>> + u8 epp;
>>
>> ret = sscanf(buf, "%20s", str_preference);
>> if (ret != 1)
>> @@ -1239,7 +1164,29 @@ static ssize_t store_energy_performance_preference(
>> if (ret < 0)
>> return -EINVAL;
>>
>> - ret = amd_pstate_set_energy_pref_index(policy, ret);
>> + if (!ret)
>> + epp = cpudata->epp_default;
>> + else
>> + epp = epp_values[ret];
>> +
>> + if (epp > 0 && policy->policy == CPUFREQ_POLICY_PERFORMANCE) {
>> + pr_debug("EPP cannot be set under performance policy\n");
>> + return -EBUSY;
>> + }
>> +
>> + if (trace_amd_pstate_epp_perf_enabled()) {
>> + union perf_cached perf = cpudata->perf;
>> +
>> + trace_amd_pstate_epp_perf(cpudata->cpu, perf.highest_perf,
>> + epp,
>> + FIELD_GET(AMD_CPPC_MIN_PERF_MASK, cpudata->cppc_req_cached),
>> + FIELD_GET(AMD_CPPC_MAX_PERF_MASK, cpudata->cppc_req_cached),
>> + policy->boost_enabled,
>> + FIELD_GET(AMD_CPPC_EPP_PERF_MASK,
>> + cpudata->cppc_req_cached) != epp);
>
> We are doing the tracing in amd_pstate_set_epp() as well right?, Isnt this one redundant?

Yup! Great catch.

>
>> + }
>> +
>> + ret = amd_pstate_set_epp(policy, epp);
>>
>> return ret ? ret : count;
>> }
>> @@ -1272,7 +1219,6 @@ static ssize_t show_energy_performance_preference(
>>
>> static void amd_pstate_driver_cleanup(void)
>> {
>> - amd_pstate_cppc_enable(false);
>> cppc_state = AMD_PSTATE_DISABLE;
>> current_pstate_driver = NULL;
>> }
>> @@ -1306,14 +1252,6 @@ static int amd_pstate_register_driver(int mode)
>>
>> cppc_state = mode;
>>
>> - ret = amd_pstate_cppc_enable(true);
>> - if (ret) {
>> - pr_err("failed to enable cppc during amd-pstate driver registration, return %d\n",
>> - ret);
>> - amd_pstate_driver_cleanup();
>> - return ret;
>> - }
>> -
>> /* at least one CPU supports CPB */
>> current_pstate_driver->boost_enabled = cpu_feature_enabled(X86_FEATURE_CPB);
>>
>> @@ -1553,11 +1491,15 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
>> policy->cpuinfo.max_freq = policy->max = perf_to_freq(perf,
>> cpudata->nominal_freq,
>> perf.highest_perf);
>> + policy->driver_data = cpudata;
>> +
>> + ret = amd_pstate_cppc_enable(policy);
>
> I think we missed cppc_enable in "amd_pstate_cpu_init". Confirmed this by booting with "amd_pstate=passive"

Yeah; true. I will add this.

>
> Also, one weird behavior I saw while testing this part, if we boot with "amd_pstate=passive"
> initially, the MSR_AMD_CPPC_ENABLE register is 0. But after I run the amd-pstate-ut (which fails
> the check_amd_pstate_enabled() test the first time) the MSR_AMD_CPPC_ENABLE gets set to 1. But I
> didnt see any code in amd-pstate-ut that sets it. We can ignore this quirk for now, just
> mentioned to see if you have any idea about this.

amd-pstate-ut will change modes, so I expect this is the reason it
happens. It's also the reason I didn't catch it. I always started in
active when I was testing switching to passive.

>
>> + if (ret)
>> + goto free_cpudata1;
>>
>> /* It will be updated by governor */
>> policy->cur = policy->cpuinfo.min_freq;
>>
>> - policy->driver_data = cpudata;
>>
>> policy->boost_enabled = READ_ONCE(cpudata->boost_supported);
>>
>> @@ -1649,31 +1591,21 @@ static int amd_pstate_epp_set_policy(struct cpufreq_policy *policy)
>> return 0;
>> }
>>
>> -static int amd_pstate_epp_reenable(struct cpufreq_policy *policy)
>> -{
>> - int ret;
>> -
>> - ret = amd_pstate_cppc_enable(true);
>> - if (ret)
>> - pr_err("failed to enable amd pstate during resume, return %d\n", ret);
>> -
>> -
>> - return amd_pstate_epp_update_limit(policy);
>> -}
>> -
>> static int amd_pstate_epp_cpu_online(struct cpufreq_policy *policy)
>> {
>> struct amd_cpudata *cpudata = policy->driver_data;
>> int ret;
>>
>> - pr_debug("AMD CPU Core %d going online\n", cpudata->cpu);
>> + pr_debug("AMD CPU Core %d going online\n", policy->cpu);
>>
>> - ret = amd_pstate_epp_reenable(policy);
>> + ret = amd_pstate_cppc_enable(policy);
>> if (ret)
>> return ret;
>> +
>> cpudata->suspended = false;
>
> Do we need this here?, shouldn't only resume() have this statement?

The reason I had in mind for it was this sequence:
* Suspend
* CPU goes offline
* CPU goes online
* Resume

But I don't think that's realistic even with parallel boot. I will drop
this.

>
>>
>> return 0;
>> +
>> }
>>
>> static int amd_pstate_epp_cpu_offline(struct cpufreq_policy *policy)
>> @@ -1691,11 +1623,6 @@ static int amd_pstate_epp_cpu_offline(struct cpufreq_policy *policy)
>> static int amd_pstate_epp_suspend(struct cpufreq_policy *policy)
>> {
>> struct amd_cpudata *cpudata = policy->driver_data;
>> - int ret;
>> -
>> - /* avoid suspending when EPP is not enabled */
>> - if (cppc_state != AMD_PSTATE_ACTIVE)
>> - return 0;
>>
>> /* invalidate to ensure it's rewritten during resume */
>> cpudata->cppc_req_cached = 0;
>> @@ -1703,11 +1630,6 @@ static int amd_pstate_epp_suspend(struct cpufreq_policy *policy)
>> /* set this flag to avoid setting core offline*/
>> cpudata->suspended = true;
>>
>> - /* disable CPPC in lowlevel firmware */
>> - ret = amd_pstate_cppc_enable(false);
>> - if (ret)
>> - pr_err("failed to suspend, return %d\n", ret);
>> -
>> return 0;
>> }
>>
>> @@ -1716,8 +1638,12 @@ static int amd_pstate_epp_resume(struct cpufreq_policy *policy)
>> struct amd_cpudata *cpudata = policy->driver_data;
>>
>> if (cpudata->suspended) {
>> + int ret;
>> +
>> /* enable amd pstate from suspend state*/
>> - amd_pstate_epp_reenable(policy);
>> + ret = amd_pstate_epp_update_limit(policy);
>> + if (ret)
>> + return ret;
>>
>> cpudata->suspended = false;
>> }
>> @@ -1732,8 +1658,6 @@ static struct cpufreq_driver amd_pstate_driver = {
>> .fast_switch = amd_pstate_fast_switch,
>> .init = amd_pstate_cpu_init,
>> .exit = amd_pstate_cpu_exit,
>> - .suspend = amd_pstate_cpu_suspend,
>> - .resume = amd_pstate_cpu_resume,
>> .set_boost = amd_pstate_set_boost,
>> .update_limits = amd_pstate_update_limits,
>> .name = "amd-pstate",
>> @@ -1748,8 +1672,8 @@ static struct cpufreq_driver amd_pstate_epp_driver = {
>> .exit = amd_pstate_epp_cpu_exit,
>> .offline = amd_pstate_epp_cpu_offline,
>> .online = amd_pstate_epp_cpu_online,
>> - .suspend = amd_pstate_epp_suspend,
>> - .resume = amd_pstate_epp_resume,
>> + .suspend = amd_pstate_epp_suspend,
>> + .resume = amd_pstate_epp_resume,
>
> Spurious whitespace change?
>
>> .update_limits = amd_pstate_update_limits,
>> .set_boost = amd_pstate_set_boost,
>> .name = "amd-pstate-epp",
>> @@ -1900,7 +1824,6 @@ static int __init amd_pstate_init(void)
>>
>> global_attr_free:
>> cpufreq_unregister_driver(current_pstate_driver);
>> - amd_pstate_cppc_enable(false);
>> return ret;
>> }
>> device_initcall(amd_pstate_init);
>