Re: [PATCH v2 1/3] cppc_cpufreq: Return desired perf in ->get() if feedback counters are 0

Jie Zhan
2024-09-19T01:17:58Z

On 18/09/2024 18:15, Ionela Voinescu wrote:
> Hi,
>
> On Wednesday 18 Sep 2024 at 10:05:13 (+0800), Jie Zhan wrote:
>>
>>
>> On 17/09/2024 18:36, Ionela Voinescu wrote:
>>
>> ...
>>
>>>>> @@ -747,19 +750,22 @@ static unsigned int cppc_cpufreq_get_rate(unsigned int cpu)
>>>>> cpufreq_cpu_put(policy);
>>>>>
>>>>> ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t0);
>>>>> - if (ret)
>>>>> - return 0;
>>>>> -
>>>>> - udelay(2); /* 2usec delay between sampling */
>>>>> -
>>>>> - ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t1);
>>>>> - if (ret)
>>>>> - return 0;
>>>>> + if (!ret) {
>>>>> + udelay(2); /* 2usec delay between sampling */
>>>>> + ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t1);
>>>>> + }
>>>>> + if (!ret)
>>>>> + delivered_perf = cppc_perf_from_fbctrs(cpu_data, &fb_ctrs_t0,
>>>>> + &fb_ctrs_t1);
>>>>
>>>> TBH, 'if (!ret)' style looks very strange to me.
>>>> We haven't done so anywhere in cppc_cpufreq, so let's keep consistency and make
>>>> it easier for people to read and maintain?
>>>
>>> I agree it's a bit of a difficult read, that's why I only sent my code
>>> as a suggestion. I did like the benefit of not having to have two
>>> different calls to cppc_perf_to_khz() and making the code below common
>>> for the error and non-error paths. But it's up to you.
>>
>> Yeah understood. I did try minimizing duplicate code, but ended up with either
>> duplicate 'get desired perf' stuff or duplicate cppc_perf_to_khz().
>>
>> ...
>>>>
>>>> delivered_perf = cppc_perf_from_fbctrs(cpu_data, &fb_ctrs_t0,
>>>> &fb_ctrs_t1);
>>>
>>> You need a check here for !delivered_perf (when at least one of the
>>> deltas is 0) in which case it would be good to take the same error path
>>> below. Something like:
>>>
>>> if(delivered_perf)
>>> return cppc_perf_to_khz(&cpu_data->perf_caps, delivered_perf);
>>> else
>>> ret = -EFAULT;
>>>
>>> That's why I did the tricky if/else dance above as we need to take the
>>> error path below for multiple cases.
>>>
>>> Thanks,
>>> Ionela.
>>>
>>
>> Sure, thanks for reminding this.
>>
>> ...
>>
>> How does this look? I think this should have the least duplicate code except for
>> two cppc_perf_to_khz() calls, while keeping the logic easy to follow.
>>
>> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
>> index bafa32dd375d..6070444ed098 100644
>> --- a/drivers/cpufreq/cppc_cpufreq.c
>> +++ b/drivers/cpufreq/cppc_cpufreq.c
>> @@ -118,6 +118,9 @@ static void cppc_scale_freq_workfn(struct kthread_work *work)
>>
>> perf = cppc_perf_from_fbctrs(cpu_data, &cppc_fi->prev_perf_fb_ctrs,
>> &fb_ctrs);
>> + if (!perf)
>> + return;
>> +
>> cppc_fi->prev_perf_fb_ctrs = fb_ctrs;
>>
>> perf <<= SCHED_CAPACITY_SHIFT;
>> @@ -726,11 +729,27 @@ static int cppc_perf_from_fbctrs(struct cppc_cpudata *cpu_data,
>>
>> /* Check to avoid divide-by zero and invalid delivered_perf */
>> if (!delta_reference || !delta_delivered)
>> - return cpu_data->perf_ctrls.desired_perf;
>> + return 0;
>>
>> return (reference_perf * delta_delivered) / delta_reference;
>> }
>>
>> +static int cppc_get_perf_ctrs_sample(int cpu,
>> + struct cppc_perf_fb_ctrs *fb_ctrs_t0,
>> + struct cppc_perf_fb_ctrs *fb_ctrs_t1)
>> +{
>> + int ret;
>> +
>> + ret = cppc_get_perf_ctrs(cpu, fb_ctrs_t0);
>> + if (ret)
>> + return ret;
>> +
>> + udelay(2); /* 2usec delay between sampling */
>> +
>> + ret = cppc_get_perf_ctrs(cpu, fb_ctrs_t1);
>
> nit: white line before return.
>
>> + return ret;
>> +}
>> +
>> static unsigned int cppc_cpufreq_get_rate(unsigned int cpu)
>> {
>> struct cppc_perf_fb_ctrs fb_ctrs_t0 = {0}, fb_ctrs_t1 = {0};
>> @@ -746,20 +765,30 @@ static unsigned int cppc_cpufreq_get_rate(unsigned int cpu)
>>
>> cpufreq_cpu_put(policy);
>>
>> - ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t0);
>> - if (ret)
>> - return 0;
>> -
>> - udelay(2); /* 2usec delay between sampling */
>> -
>> - ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t1);
>> - if (ret)
>> - return 0;
>> + ret = cppc_get_perf_ctrs_sample(cpu, &fb_ctrs_t0, &fb_ctrs_t1);
>> + if (ret) {
>> + if (ret == -EFAULT)
>> + goto out_invalid_counters;
>> + else
>> + return 0;
>> + }
>>
>> delivered_perf = cppc_perf_from_fbctrs(cpu_data, &fb_ctrs_t0,
>> &fb_ctrs_t1);
>> + if (!delivered_perf)
>> + goto out_invalid_counters;
>>
>> return cppc_perf_to_khz(&cpu_data->perf_caps, delivered_perf);
>> +
>> +out_invalid_counters:
>> + /*
>> + * Feedback counters could be unchanged or 0 when a cpu enters a
>> + * low-power idle state, e.g. clock-gated or power-gated.
>> + * Get the lastest or cached desired perf for reflecting frequency.
>> + */
>> + if (cppc_get_desired_perf(cpu, &delivered_perf))
>> + delivered_perf = cpu_data->perf_ctrls.desired_perf;
>
> nit: same white line before return here :).
>
> Looks good, thanks for the changes.
>
> Reviewed-by: Ionela Voinescu <ionela.voinescu@arm.com>
>
> Ionela.

Sure, thanks. I'll send a V3 based on this.

Jie

>
>> + return cppc_perf_to_khz(&cpu_data->perf_caps, delivered_perf);
>> }
>>
>> static int cppc_cpufreq_set_boost(struct cpufreq_policy *policy, int state)
>>
>>
>> Thanks!
>> Jie
>