Re: [PATCH v3 10/15] cpufreq/amd-pstate: Move limit updating code

[Dhananjay Ugwekar <Dhananjay.Ugwekar@amd.com>]

On 12/16/2024 7:51 PM, Mario Limonciello wrote:
> On 12/16/2024 08:16, Dhananjay Ugwekar wrote:
>> Hello Mario,
>>
>> On 12/10/2024 12:22 AM, Mario Limonciello wrote:
>>> The limit updating code in amd_pstate_epp_update_limit() should not
>>> only apply to EPP updates.  Move it to amd_pstate_update_min_max_limit()
>>> so other callers can benefit as well.
>>>
>>> With this move it's not necessary to have clamp_t calls anymore because
>>> the verify callback is called when setting limits.
>>
>> While testing this series, I observed that with amd_pstate=passive + schedutil governor,
>> the scaling_max_freq limits were not being honored and I bisected the issue down to this
>> patch.
>>
>> I went through the code and noticed that in amd_pstate_adjust_perf(), we set the min_perf
>> field in MSR_AMD_CPPC_REQ to "cap_perf" which is equal to cpudata->highest_perf (which is
>> equal to 255 for non-preferred cores systems). This didnt seem logical to me and I changed
>> cap_perf to cpudata->max_limit_perf which gives us the value updated in scaling_max_freq.
>>
>> I think as we removed the redundant clamping code, this pre-existing issue got exposed.
>> The below diff fixes the issue for me.
>>
>> Please let me know your thoughts on this.
>>
>> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
>> index d7b1de97727a..1ac34e3f1fc5 100644
>> --- a/drivers/cpufreq/amd-pstate.c
>> +++ b/drivers/cpufreq/amd-pstate.c
>> @@ -699,7 +699,7 @@ static void amd_pstate_adjust_perf(unsigned int cpu,
>>          if (min_perf < lowest_nonlinear_perf)
>>                  min_perf = lowest_nonlinear_perf;
here^^^
>>
>> -       max_perf = cap_perf;
>> +       max_perf = cpudata->max_limit_perf;
>>          if (max_perf < min_perf)
>>                  max_perf = min_perf;
> 
> With this change I think you can also drop the comparison afterwards, as an optimization right?

Umm I think it is possible that scaling_max_freq is set to a value lower than 
lowest_nonlinear_freq in that case this if condition would be needed (as min_perf 
is being lower bounded at lowest_nonlinear_freq at the location highlighted above). 
I would be okay with keeping this check in. 

Also, what is the behavior if max_perf is set to a value lower than min_perf in 
the CPPC_REQ MSR? I guess platform FW would also be smart enough to handle this 
implicitly, but cant say for sure.

> 
> As this is already in superm1.git/linux-next after testing can you please send a patch relative to superm1.git/linux-next branch?

Sure, I'll send out the patch once we finalize on the above if condition.

Regards,
Dhananjay

> 
> Thanks!
> 
>>
>> Thanks,
>> Dhananjay
>>
>>>
>>> Reviewed-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
>>> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
>>> ---
>>> v2:
>>>   * Drop lowest_perf variable
>>> ---
>>>   drivers/cpufreq/amd-pstate.c | 28 +++++-----------------------
>>>   1 file changed, 5 insertions(+), 23 deletions(-)
>>>
>>> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
>>> index 3a3df67c096d5..dc3c45b6f5103 100644
>>> --- a/drivers/cpufreq/amd-pstate.c
>>> +++ b/drivers/cpufreq/amd-pstate.c
>>> @@ -537,10 +537,6 @@ static void amd_pstate_update(struct amd_cpudata *cpudata, u32 min_perf,
>>>       u32 nominal_perf = READ_ONCE(cpudata->nominal_perf);
>>>       u64 value = prev;
>>>   -    min_perf = clamp_t(unsigned long, min_perf, cpudata->min_limit_perf,
>>> -            cpudata->max_limit_perf);
>>> -    max_perf = clamp_t(unsigned long, max_perf, cpudata->min_limit_perf,
>>> -            cpudata->max_limit_perf);
>>>       des_perf = clamp_t(unsigned long, des_perf, min_perf, max_perf);
>>>         max_freq = READ_ONCE(cpudata->max_limit_freq);
>>> @@ -607,7 +603,7 @@ static int amd_pstate_verify(struct cpufreq_policy_data *policy_data)
>>>     static int amd_pstate_update_min_max_limit(struct cpufreq_policy *policy)
>>>   {
>>> -    u32 max_limit_perf, min_limit_perf, lowest_perf, max_perf, max_freq;
>>> +    u32 max_limit_perf, min_limit_perf, max_perf, max_freq;
>>>       struct amd_cpudata *cpudata = policy->driver_data;
>>>         max_perf = READ_ONCE(cpudata->highest_perf);
>>> @@ -615,12 +611,8 @@ static int amd_pstate_update_min_max_limit(struct cpufreq_policy *policy)
>>>       max_limit_perf = div_u64(policy->max * max_perf, max_freq);
>>>       min_limit_perf = div_u64(policy->min * max_perf, max_freq);
>>>   -    lowest_perf = READ_ONCE(cpudata->lowest_perf);
>>> -    if (min_limit_perf < lowest_perf)
>>> -        min_limit_perf = lowest_perf;
>>> -
>>> -    if (max_limit_perf < min_limit_perf)
>>> -        max_limit_perf = min_limit_perf;
>>> +    if (cpudata->policy == CPUFREQ_POLICY_PERFORMANCE)
>>> +        min_limit_perf = min(cpudata->nominal_perf, max_limit_perf);
>>>         WRITE_ONCE(cpudata->max_limit_perf, max_limit_perf);
>>>       WRITE_ONCE(cpudata->min_limit_perf, min_limit_perf);
>>> @@ -1562,28 +1554,18 @@ static void amd_pstate_epp_cpu_exit(struct cpufreq_policy *policy)
>>>   static int amd_pstate_epp_update_limit(struct cpufreq_policy *policy)
>>>   {
>>>       struct amd_cpudata *cpudata = policy->driver_data;
>>> -    u32 max_perf, min_perf;
>>>       u64 value;
>>>       s16 epp;
>>>   -    max_perf = READ_ONCE(cpudata->highest_perf);
>>> -    min_perf = READ_ONCE(cpudata->lowest_perf);
>>>       amd_pstate_update_min_max_limit(policy);
>>>   -    max_perf = clamp_t(unsigned long, max_perf, cpudata->min_limit_perf,
>>> -            cpudata->max_limit_perf);
>>> -    min_perf = clamp_t(unsigned long, min_perf, cpudata->min_limit_perf,
>>> -            cpudata->max_limit_perf);
>>>       value = READ_ONCE(cpudata->cppc_req_cached);
>>>   -    if (cpudata->policy == CPUFREQ_POLICY_PERFORMANCE)
>>> -        min_perf = min(cpudata->nominal_perf, max_perf);
>>> -
>>>       value &= ~(AMD_CPPC_MAX_PERF_MASK | AMD_CPPC_MIN_PERF_MASK |
>>>              AMD_CPPC_DES_PERF_MASK);
>>> -    value |= FIELD_PREP(AMD_CPPC_MAX_PERF_MASK, max_perf);
>>> +    value |= FIELD_PREP(AMD_CPPC_MAX_PERF_MASK, cpudata->max_limit_perf);
>>>       value |= FIELD_PREP(AMD_CPPC_DES_PERF_MASK, 0);
>>> -    value |= FIELD_PREP(AMD_CPPC_MIN_PERF_MASK, min_perf);
>>> +    value |= FIELD_PREP(AMD_CPPC_MIN_PERF_MASK, cpudata->min_limit_perf);
>>>         /* Get BIOS pre-defined epp value */
>>>       epp = amd_pstate_get_epp(cpudata, value);
>>
>