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

[Mario Limonciello <mario.limonciello@amd.com>]

On 12/16/2024 08:45, Dhananjay Ugwekar wrote:
> 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.

Well this feels like a bigger problem actually - why is it forcefully 
bounded at lowest nonlinear freq?  Performance is going to be awful at 
that level (hence why commit 5d9a354cf839a ("cpufreq/amd-pstate: Set the 
initial min_freq to lowest_nonlinear_freq") was done),

but shouldn't we "let" people go below that in passive and guided?  We 
do for active.

> 
> 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.
> 

I would hope so too; but yeah you're right we don't know 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);
>>>
>>
>