linux-kernel - Re: [PATCH] arch_topology: Trace the update thermal pressure

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Date:   Thu, 21 Apr 2022 07:26:36 +0100
From:   Lukasz Luba <lukasz.luba@....com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, sudeep.holla@....com,
        dietmar.eggemann@....com, vincent.guittot@...aro.org,
        gregkh@...uxfoundation.org, rafael@...nel.org, mingo@...hat.com
Subject: Re: [PATCH] arch_topology: Trace the update thermal pressure



On 4/21/22 00:44, Steven Rostedt wrote:
> On Tue, 19 Apr 2022 17:48:01 +0100
> Lukasz Luba <lukasz.luba@....com> wrote:
> 
>> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
>> index 1d6636ebaac5..4f0392de3081 100644
>> --- a/drivers/base/arch_topology.c
>> +++ b/drivers/base/arch_topology.c
>> @@ -19,6 +19,8 @@
>>   #include <linux/rcupdate.h>
>>   #include <linux/sched.h>
>>   
>> +#include <trace/events/thermal.h>
>> +
>>   static DEFINE_PER_CPU(struct scale_freq_data __rcu *, sft_data);
>>   static struct cpumask scale_freq_counters_mask;
>>   static bool scale_freq_invariant;
>> @@ -195,6 +197,8 @@ void topology_update_thermal_pressure(const struct cpumask *cpus,
>>   
>>   	th_pressure = max_capacity - capacity;
>>   
>> +	trace_thermal_pressure_update(cpu, th_pressure);
>> +
>>   	for_each_cpu(cpu, cpus)
>>   		WRITE_ONCE(per_cpu(thermal_pressure, cpu), th_pressure);
>>   }
>> diff --git a/include/trace/events/thermal.h b/include/trace/events/thermal.h
>> index 8a5f04888abd..1bf08ee1a25b 100644
>> --- a/include/trace/events/thermal.h
>> +++ b/include/trace/events/thermal.h
>> @@ -65,6 +65,25 @@ TRACE_EVENT(cdev_update,
>>   	TP_printk("type=%s target=%lu", __get_str(type), __entry->target)
>>   );
>>   
>> +TRACE_EVENT(thermal_pressure_update,
>> +
>> +	TP_PROTO(int cpu, unsigned long thermal_pressure),
>> +
>> +	TP_ARGS(cpu, thermal_pressure),
>> +
>> +	TP_STRUCT__entry(
>> +		__field(int, cpu)
>> +		__field(unsigned long, thermal_pressure)
> 
> Note, it is always best to place the bigger object before the smaller one
> (when not properly aligned), as that will help to prevent structure
> "holes". That is:
> 
> 		__field(unsigned long, thermal_pressure)
> 		__field(int, cpu)
> 
> 
> Otherwise, you are pretty much guaranteed to have a 4 byte hole between cpu
> and thermal_pressure on 64 bit machines.
> 
> Also, for the warning you got from the test robot, if you are using this in
> a module and defining it in the core kernel, you need to add:
> 
> EXPORT_TRACEPOINT_SYMBOL_GPL(thermal_pressure_update);
> 
> Somewhere in the C file that includes this file and defines
> CREATE_TRACE_POINTS.
> 
> -- Steve
> 
> 

Thank you Steve, I'll swap those fields and add the needed export.
I have to go through those older trace events in that file and
understand if they are correct, since I just followed the pattern
in 'cdev_update'.

Regards,
Lukasz