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

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Mon, 20 Dec 2021 17:39:09 +0100

On Mon, Dec 20 2021, Jeff Hostetler via GitGitGadget wrote:

> From: Jeff Hostetler <[email-masked]>
>
> Teach Trace2 "perf" and "event" formats to handle "timer" events for
> stopwatch timers.  Update API documentation accordingly.
>
> In a future commit, stopwatch timers will be added to the Trace2 API
> and it will emit these "timer" events.
>
> Signed-off-by: Jeff Hostetler <[email-masked]>
> ---
>  Documentation/technical/api-trace2.txt | 25 +++++++++++++++-
>  trace2/tr2_tgt.h                       | 25 ++++++++++++++++
>  trace2/tr2_tgt_event.c                 | 40 +++++++++++++++++++++++++-
>  trace2/tr2_tgt_normal.c                |  1 +
>  trace2/tr2_tgt_perf.c                  | 29 +++++++++++++++++++
>  5 files changed, 118 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/technical/api-trace2.txt b/Documentation/technical/api-trace2.txt
> index bb13ca3db8b..e6ed94ba814 100644
> --- a/Documentation/technical/api-trace2.txt
> +++ b/Documentation/technical/api-trace2.txt
> @@ -391,7 +391,7 @@ only present on the "start" and "atexit" events.
>  {
>  	"event":"version",
>  	...
> -	"evt":"3",		       # EVENT format version
> +	"evt":"4",		       # EVENT format version
>  	"exe":"2.20.1.155.g426c96fcdb" # git version
>  }

FWIW this seems like a time not to bump the version per the proposed
approach in:
https://lore.kernel.org/git/[email-masked]/

Not directly related to this series, which just preserves the status
quo, but it would be nice to get feedback on that proposal from you.

> [...]
> + * Verison 1: original version

A typo of "Version".

> + * Version 2: added "too_many_files" event
> + * Version 3: added "child_ready" event
> + * Version 4: added "timer" event
>   */
> -#define TR2_EVENT_VERSION "3"
> +#define TR2_EVENT_VERSION "4"
>  
>  /*
>   * Region nesting limit for messages written to the event target.
> @@ -615,6 +620,38 @@ static void fn_data_json_fl(const char *file, int line,
>  	}
>  }
>  
> +static void fn_timer(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 *event_name = "timer";
> +	struct json_writer jw = JSON_WRITER_INIT;
> +	double t_abs = (double)us_elapsed_absolute / 1000000.0;
> +

nit: Odd placement of \n\n

> +	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;

Both for this...

> +	jw_object_begin(&jw, 0);
> +	event_fmt_prepare(event_name, __FILE__, __LINE__, NULL, &jw, thread_name);
> +	jw_object_double(&jw, "t_abs", 6, t_abs);
> +	jw_object_string(&jw, "name", timer_name);
> +	jw_object_intmax(&jw, "count", interval_count);
> +	jw_object_double(&jw, "t_total", 6, t_total);
> +	jw_object_double(&jw, "t_min", 6, t_min);
> +	jw_object_double(&jw, "t_max", 6, t_max);

[...]

> +static void fn_timer(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 *event_name = "timer";
> +	struct strbuf buf_payload = STRBUF_INIT;
> +
> +	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;
> +
> +	strbuf_addf(&buf_payload, "name:%s", timer_name);
> +	strbuf_addf(&buf_payload, " count:%"PRIu64, interval_count);
> +	strbuf_addf(&buf_payload, " total:%9.6f", t_total);
> +	strbuf_addf(&buf_payload, " min:%9.6f", t_min);
> +	strbuf_addf(&buf_payload, " max:%9.6f", t_max);

...and this, wouldn't it be better/more readable to retain the uint64_t
for the math, and just cast if needed when we're doing the formatting?