Re: [PATCH 12/32] tracing: Add hist trigger timestamp support

Namhyung Kim
2017-07-17T06:01:36Z

On Mon, Jun 26, 2017 at 05:49:13PM -0500, Tom Zanussi wrote:
> Add support for a timestamp event field. This is actually a 'pseudo-'
> event field in that it behaves like it's part of the event record, but
> is really part of the corresponding ring buffer event.
>
> To make use of the timestamp field, users can specify
> "$common_timestamp" as a field name for any histogram. Note that this
> doesn't make much sense on its own either as either a key or value,
> but needs to be supported even so, since follow-on patches will add
> support for making use of this field in time deltas. The '$' is used
> as a prefix on the variable name to indicate that it's not an bonafide
> event field - so you won't find it in the event description - but
> rather it's a synthetic field that can be used like a real field).
>
> Note that the use of this field requires the ring buffer be put into
> TIME_EXTEND_ABS mode, which saves the complete timestamp for each
> event rather than an offset. This mode will be enabled if and only if
> a histogram makes use of the "$common_timestamp" field.
>
> Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
> ---
> kernel/trace/trace_events_hist.c | 90 +++++++++++++++++++++++++++++-----------
> 1 file changed, 66 insertions(+), 24 deletions(-)
>
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index dab6ff6..aeae3b4 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c

[SNIP]
> @@ -756,7 +783,7 @@ static int create_sort_keys(struct hist_trigger_data *hist_data)
> break;
> }
>
> - if (strcmp(field_name, "hitcount") == 0) {
> + if ((strcmp(field_name, "hitcount") == 0)) {

Seems like an unnecessary change.

> descending = is_descending(field_str);
> if (descending < 0) {
> ret = descending;
> @@ -816,6 +843,9 @@ static int create_tracing_map_fields(struct hist_trigger_data *hist_data)
>
> if (hist_field->flags & HIST_FIELD_FL_STACKTRACE)
> cmp_fn = tracing_map_cmp_none;
> + else if (!field)
> + cmp_fn = tracing_map_cmp_num(hist_field->size,
> + hist_field->is_signed);

I couldn't find where the hist_field->is_signed is set.

> else if (is_string_field(field))
> cmp_fn = tracing_map_cmp_string;
> else

[SNIP]
> @@ -1534,6 +1570,9 @@ static int hist_register_trigger(char *glob, struct event_trigger_ops *ops,
>
> update_cond_flag(file);
>
> + if (hist_data->enable_timestamps)
> + tracing_set_time_stamp_abs(file->tr, true);
> +
> if (trace_event_trigger_enable_disable(file, 1) < 0) {
> list_del_rcu(&data->list);
> update_cond_flag(file);
> @@ -1568,6 +1607,9 @@ static void hist_unregister_trigger(char *glob, struct event_trigger_ops *ops,
>
> if (unregistered && test->ops->free)
> test->ops->free(test->ops, test);
> +
> + if (hist_data->enable_timestamps)
> + tracing_set_time_stamp_abs(file->tr, false);

I think it needs some kind of refcount to disable the absolute
timestamp. Otherwise unregistering a timestamp-enabled hist might
corrupt others IMHO.

Thanks,
Namhyung

> }
>
> static void hist_unreg_all(struct trace_event_file *file)
> --
> 1.9.3
>