[05/17] trace: energy_model: Add trace event for EM runtime modifications

The Energy Model (EM) supports runtime modifications. Track the changes
in order to do post-processing analysis. Don't use arrays in the trace
event, since they are not properly supported by the tools. Instead use
simple "unroll" with emitting the trace event for each EM array entry
with proper ID information. The older debugging mechanism which was
the simple debugfs which dumping the EM content won't be sufficient for
the modifiable EM purpose. This trace event mechanism would address the
needs.

Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
---
 include/trace/events/energy_model.h | 46 +++++++++++++++++++++++++++++
 kernel/power/energy_model.c         |  3 ++
 2 files changed, 49 insertions(+)
 create mode 100644 include/trace/events/energy_model.h

Hello Lukasz,
Just a suggestion, maybe it would be good to trace the CPUs affected by
the modification. It is possible to retrieve this information by going
to /sys/kernel/debug/energy_model/xxx/cpus, but might be simpler when
parsing a trace.

Regards,
Pierre

On 3/14/23 11:33, Lukasz Luba wrote:
> The Energy Model (EM) supports runtime modifications. Track the changes
> in order to do post-processing analysis. Don't use arrays in the trace
> event, since they are not properly supported by the tools. Instead use
> simple "unroll" with emitting the trace event for each EM array entry
> with proper ID information. The older debugging mechanism which was
> the simple debugfs which dumping the EM content won't be sufficient for
> the modifiable EM purpose. This trace event mechanism would address the
> needs.
> 
> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
> ---
>   include/trace/events/energy_model.h | 46 +++++++++++++++++++++++++++++
>   kernel/power/energy_model.c         |  3 ++
>   2 files changed, 49 insertions(+)
>   create mode 100644 include/trace/events/energy_model.h
> 
> diff --git a/include/trace/events/energy_model.h b/include/trace/events/energy_model.h
> new file mode 100644
> index 000000000000..f70babeb5dde
> --- /dev/null
> +++ b/include/trace/events/energy_model.h
> @@ -0,0 +1,46 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM energy_model
> +
> +#if !defined(_TRACE_ENERGY_MODEL_H) || defined(TRACE_HEADER_MULTI_READ)
> +#define _TRACE_ENERGY_MODEL_H
> +
> +#include <linux/tracepoint.h>
> +
> +TRACE_EVENT(em_perf_state,
> +	TP_PROTO(const char *dev_name, int nr_perf_states, int state,
> +		 unsigned long ps_frequency, unsigned long ps_power,
> +		 unsigned long ps_cost, unsigned long ps_flags),
> +
> +	TP_ARGS(dev_name, nr_perf_states, state, ps_frequency, ps_power, ps_cost,
> +		ps_flags),
> +
> +	TP_STRUCT__entry(
> +		__string(name, dev_name)
> +		__field(int, num_states)
> +		__field(int, state)
> +		__field(unsigned long, frequency)
> +		__field(unsigned long, power)
> +		__field(unsigned long, cost)
> +		__field(unsigned long, flags)
> +	),
> +
> +	TP_fast_assign(
> +		__assign_str(name, dev_name);
> +		__entry->num_states = nr_perf_states;
> +		__entry->state = state;
> +		__entry->frequency = ps_frequency;
> +		__entry->power = ps_power;
> +		__entry->cost = ps_cost;
> +		__entry->flags = ps_flags;
> +	),
> +
> +	TP_printk("dev_name=%s nr_perf_states=%d state=%d frequency=%lu power=%lu cost=%lu flags=%lu",
> +		__get_str(name), __entry->num_states, __entry->state,
> +		__entry->frequency, __entry->power, __entry->cost,
> +		__entry->flags)
> +);
> +#endif /* _TRACE_ENERGY_MODEL_H */
> +
> +/* This part must be outside protection */
> +#include <trace/define_trace.h>
> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
> index 937e98a71ed5..3b778743ba89 100644
> --- a/kernel/power/energy_model.c
> +++ b/kernel/power/energy_model.c
> @@ -17,6 +17,9 @@
>   #include <linux/sched/topology.h>
>   #include <linux/slab.h>
>   
> +#define CREATE_TRACE_POINTS
> +#include <trace/events/energy_model.h>
> +
>   /*
>    * Mutex serializing the registrations of performance domains and letting
>    * callbacks defined by drivers sleep.

On 4/11/23 16:39, Pierre Gondois wrote:
> Hello Lukasz,
> Just a suggestion, maybe it would be good to trace the CPUs affected by

We print the device name in the trace event, which would be the first
CPU in the frequency domain.

> the modification. It is possible to retrieve this information by going
> to /sys/kernel/debug/energy_model/xxx/cpus, but might be simpler when
> parsing a trace.

We don't want to introduce an array of CPUs, or a name like cpus0-3,
which than has to be parsed in more complex way. Also, the other devices
like GPU might use this trace event, so I just wanted to keep it simple
and generic to handle them all.