[PATCH v3 1/2] cppc_cpufreq: Use desired perf if feedback ctrs are 0 or unchanged
lihuisong (C)
lihuisong at huawei.com
Wed Sep 25 23:07:33 PDT 2024
在 2024/9/26 10:57, Jie Zhan 写道:
>
> On 25/09/2024 17:28, lihuisong (C) wrote:
>> Hi Jie,
>>
>> LGTM except for some trivial,
>> Reviewed-by: Huisong Li <lihuisong at huawei.com>
> Thanks.
>
>>
>> 在 2024/9/19 16:45, Jie Zhan 写道:
>>> The CPPC performance feedback counters could be 0 or unchanged when the
>>> target cpu is in a low-power idle state, e.g. power-gated or clock-gated.
>>>
>>> When the counters are 0, cppc_cpufreq_get_rate() returns 0 KHz, which makes
>>> cpufreq_online() get a false error and fail to generate a cpufreq policy.
>>>
>>> When the counters are unchanged, the existing cppc_perf_from_fbctrs()
>>> returns a cached desired perf, but some platforms may update the real
>>> frequency back to the desired perf reg.
>>>
>>> For the above cases in cppc_cpufreq_get_rate(), get the latest desired perf
>>> to reflect the frequency; if failed, return the cached desired perf.
>>>
>>> Fixes: 6a4fec4f6d30 ("cpufreq: cppc: cppc_cpufreq_get_rate() returns zero in all error cases.")
>>> Signed-off-by: Jie Zhan <zhanjie9 at hisilicon.com>
>>> Reviewed-by: Zeng Heng <zengheng4 at huawei.com>
>>> Reviewed-by: Ionela Voinescu <ionela.voinescu at arm.com>
>>> ---
>>> drivers/cpufreq/cppc_cpufreq.c | 49 +++++++++++++++++++++++++++-------
>>> 1 file changed, 39 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
>>> index bafa32dd375d..e55192303a9f 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 +729,26 @@ static int cppc_perf_from_fbctrs(struct cppc_cpudata *cpu_data,
>>> /* Check to avoid divide-by zero and invalid delivered_perf */
>> Now this comment can be removed, right?
> Didn't notice this comment, but, having a check, I think it still fits.
> '!delta_reference' avoids divide-by zero, and '!delta_delivered' checks
> invalid delivered_perf.
The comment "avoid divide-by zero" is just for the below code:
"(reference_perf * delta_delivered) / delta_reference".
So It is also useful, but I think It's obvious and it doesn't make much
sense.
The comment "avoid invalid delivered_perf" is for the return value.
Now this func return zero which can't count as a valid delivered_perf,
right?
>
> So I think we just leave it unchanged.
>
>>> 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 */
>>> +
>>> + return cppc_get_perf_ctrs(cpu, fb_ctrs_t1);
>>> +}
>>> +
>>> static unsigned int cppc_cpufreq_get_rate(unsigned int cpu)
>>> {
>>> struct cppc_perf_fb_ctrs fb_ctrs_t0 = {0}, fb_ctrs_t1 = {0};
>>> @@ -746,18 +764,29 @@ 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;
>> suggest that add some comments for ret == -EFAULT case.
>> Because this error code depands on the implementation of cppc_get_perf_ctrs.
>> If add a new exception case which also return -EFAULT, then this switch is unreasonable.
> Sure. What about adding the following comment:
>
> /* -EFAULT indicates that any of the associated CPPC regs is 0. */
Ack
> .
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