Re: [PATCH] arch_topology: Trace the update thermal pressure

[Lukasz Luba]

On 4/21/22 00:44, Steven Rostedt wrote:
> On Tue, 19 Apr 2022 17:48:01 +0100
> Lukasz Luba <lukasz.luba@xxxxxxx> 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