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Message-ID: <72de6a0f-f8c9-2b3d-04b5-613f2d368b61@huawei.com>
Date: Thu, 18 May 2023 09:44:48 +0800
From: Zeng Heng <zengheng4@...wei.com>
To: Sumit Gupta <sumitg@...dia.com>,
Pierre Gondois <pierre.gondois@....com>,
Ionela Voinescu <Ionela.Voinescu@....com>
CC: <linux-kernel@...r.kernel.org>, <linux-pm@...r.kernel.org>,
<wangxiongfeng2@...wei.com>, <xiexiuqi@...wei.com>,
<liwei391@...wei.com>, <linux-acpi@...r.kernel.org>,
<weiyongjun1@...wei.com>, <lenb@...nel.org>,
<viresh.kumar@...aro.org>, <rafael@...nel.org>,
Yang Shi <yang@...amperecomputing.com>
Subject: Re: [PATCH v2 1/2] cpufreq: CPPC: keep target core awake when reading
its cpufreq rate
在 2023/5/17 23:03, Sumit Gupta 写道:
>
>
> On 17/05/23 13:47, Pierre Gondois wrote:
>> External email: Use caution opening links or attachments
>>
>>
>> +Ionela, Sumit, Yang,
>>
>> Hello Zeng,
>>
>> I think solutions around related issues were suggested at:
>>
>> [1]
>> https://lore.kernel.org/all/20230418113459.12860-7-sumitg@nvidia.com/
>> [2]
>> https://lore.kernel.org/all/20230328193846.8757-1-yang@os.amperecomputing.com/
>> [3] https://lore.kernel.org/all/ZEl1Fms%2FJmdEZsVn@arm.com/
>>
>> About this patch, it seems to mean that CPPC counters of CPUx are always
>> accessed from CPUx, even when they are not AMUs. For instance CPPC
>> counters could be memory mapped and accessible from any CPU.
>> cpu_has_amu_feat() should allow to probe if a CPU uses AMUs or not,
>> and [2] had an implementation using it.
>>
>> Another comment about PATCH 2/2 is that if the counters are accessed
>> through FFH, arm64 version of cpc_read_ffh() is calling
>> counters_read_on_cpu(), and a comment in counters_read_on_cpu() seems
>> to specify the function must be called with interrupt enabled.
>>
>> I think the best solution so far was the one at [3], suggested by
>> Ionela,
>> but it doesn't seem to solve your issue. Indeed, it is not checked
>> whether
>> the counters are AMU counters and that they must be remotely read (to
>> have the CPU awake),
>>
>> Regards,
>> Pierre
>>
>
> I think the solution in [1] is simple and solves all the three cases.
> Also, it provides better accuracy between the set and get frequency as
> compared to [3].
>
> This can be merged and can later still be improved in Upstream.
>
> If OK, I can send new version by changing the patch to apply for all
> ARM SoC's with AMU and not specific to Tegra.
>
> Thank you,
> Sumit Gupta
>
I vote solution [1] and it should be applied to all ARM SoCs with AMU.
Zeng Heng
>>
>> On 5/16/23 15:32, Zeng Heng wrote:
>>> As ARM AMU's document says, all counters are subject to any changes
>>> in clock frequency, including clock stopping caused by the WFI and WFE
>>> instructions.
>>>
>>> Therefore, using smp_call_on_cpu() to trigger target CPU to
>>> read self's AMU counters, which ensures the counters are working
>>> properly during calculation.
>>>
>>> Signed-off-by: Zeng Heng <zengheng4@...wei.com>
>>> ---
>>> drivers/cpufreq/cppc_cpufreq.c | 30 +++++++++++++++++++-----------
>>> 1 file changed, 19 insertions(+), 11 deletions(-)
>>>
>>> diff --git a/drivers/cpufreq/cppc_cpufreq.c
>>> b/drivers/cpufreq/cppc_cpufreq.c
>>> index 022e3555407c..910167f58bb3 100644
>>> --- a/drivers/cpufreq/cppc_cpufreq.c
>>> +++ b/drivers/cpufreq/cppc_cpufreq.c
>>> @@ -837,9 +837,24 @@ static int cppc_perf_from_fbctrs(struct
>>> cppc_cpudata *cpu_data,
>>> return (reference_perf * delta_delivered) / delta_reference;
>>> }
>>>
>>> +static int cppc_get_perf_ctrs_smp(void *val)
>>> +{
>>> + int cpu = smp_processor_id();
>>> + struct cppc_perf_fb_ctrs *fb_ctrs = val;
>>> + int ret;
>>> +
>>> + ret = cppc_get_perf_ctrs(cpu, fb_ctrs);
>>> + if (ret)
>>> + return ret;
>>> +
>>> + udelay(2); /* 2usec delay between sampling */
>>> +
>>> + return cppc_get_perf_ctrs(cpu, fb_ctrs + 1);
>>> +}
>>> +
>>> static unsigned int cppc_cpufreq_get_rate(unsigned int cpu)
>>> {
>>> - struct cppc_perf_fb_ctrs fb_ctrs_t0 = {0}, fb_ctrs_t1 = {0};
>>> + struct cppc_perf_fb_ctrs fb_ctrs[2] = {0};
>>> struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
>>> struct cppc_cpudata *cpu_data = policy->driver_data;
>>> u64 delivered_perf;
>>> @@ -847,19 +862,12 @@ 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 ret;
>>> -
>>> - udelay(2); /* 2usec delay between sampling */
>>> -
>>> - ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t1);
>>> + ret = smp_call_on_cpu(cpu, cppc_get_perf_ctrs_smp, fb_ctrs, 1);
>>> if (ret)
>>> return ret;
>>>
>>> - delivered_perf = cppc_perf_from_fbctrs(cpu_data, &fb_ctrs_t0,
>>> - &fb_ctrs_t1);
>>> -
>>> + delivered_perf = cppc_perf_from_fbctrs(cpu_data, fb_ctrs,
>>> + fb_ctrs + 1);
>>> return cppc_cpufreq_perf_to_khz(cpu_data, delivered_perf);
>>> }
>>>
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