Re: [PATCH 6/9] trace2: add timer events to perf and event target formats

> +`"timer"`::
> +	This event is generated at the end of the program and contains
> +	statistics for a global stopwatch timer.
> ++
> +------------
> +{
> +	"event":"timer",
> +	...
> +	"name":"test",      # timer name
> +	"count":42,         # number of start+stop intervals
> +	"t_total":1.234,    # sum of all intervals (by thread or globally)
> +	"t_min":0.1,        # shortest interval
> +	"t_max":0.9,        # longest interval

> + * stopwatch timer values to the event streams.  Unlike other Trace2 API
> + * events, this is decoupled from the data collection.
> + *
> + * This does not take a (file,line) pair because a timer event reports
> + * the cummulative time spend in the timer over a series of intervals

> + * -- it does not represent a single usage (like region or data events
> + * do).
> + *
> + * The thread name is optional.  If non-null it will override the
> + * value inherited from the caller's TLS CTX.  This allows data
> + * for global timers to be reported without associating it with a
> + * single thread.
> + */
> +typedef void(tr2_tgt_evt_timer_t)(uint64_t us_elapsed_absolute,
> +				  const char *thread_name,
> +				  const char *category,
> +				  const char *timer_name,
> +				  uint64_t interval_count,
> +				  uint64_t us_total_time,
> +				  uint64_t us_min_time,
> +				  uint64_t us_max_time);

> +		     const char *thread_name,
> +		     const char *category,
> +		     const char *timer_name,
> +		     uint64_t interval_count,
> +		     uint64_t us_total_time,
> +		     uint64_t us_min_time,
> +		     uint64_t us_max_time)
> +{
> +	const char *event_name = "timer";
> +	struct json_writer jw = JSON_WRITER_INIT;
> +	double t_abs = (double)us_elapsed_absolute / 1000000.0;
> +
> +	double t_total = (double)us_total_time / 1000000.0;
> +	double t_min   = (double)us_min_time   / 1000000.0;
> +	double t_max   = (double)us_max_time   / 1000000.0;