Re: [RFC][PATCH 09/21] tracing: Add hist trigger timestamp support

Namhyung Kim
2017-02-10T06:29:41Z

On Wed, Feb 08, 2017 at 11:25:05AM -0600, 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.
>
> 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 | 85 +++++++++++++++++++++++++++++-----------
> 1 file changed, 62 insertions(+), 23 deletions(-)
>
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index 4e70872..8d7f7dd 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -88,6 +88,12 @@ static u64 hist_field_log2(struct hist_field *hist_field, void *event,
> return (u64) ilog2(roundup_pow_of_two(val));
> }
>
> +static u64 hist_field_timestamp(struct hist_field *hist_field, void *event,
> + struct ring_buffer_event *rbe)
> +{
> + return ring_buffer_event_time_stamp(rbe);
> +}
> +
> #define DEFINE_HIST_FIELD_FN(type) \
> static u64 hist_field_##type(struct hist_field *hist_field, \
> void *event, \
> @@ -134,6 +140,7 @@ enum hist_field_flags {
> HIST_FIELD_FL_SYSCALL = 128,
> HIST_FIELD_FL_STACKTRACE = 256,
> HIST_FIELD_FL_LOG2 = 512,
> + HIST_FIELD_FL_TIMESTAMP = 1024,
> };
>
> struct hist_trigger_attrs {
> @@ -158,6 +165,7 @@ struct hist_trigger_data {
> struct trace_event_file *event_file;
> struct hist_trigger_attrs *attrs;
> struct tracing_map *map;
> + bool enable_timestamps;
> };
>
> static const char *hist_field_name(struct hist_field *field)
> @@ -404,6 +412,7 @@ static struct hist_field *create_hist_field(struct ftrace_event_field *field,
> hist_field = kzalloc(sizeof(struct hist_field), GFP_KERNEL);
> if (!hist_field)
> return NULL;
> + hist_field->is_signed = false;

I think it's not needed since hist_field is allocated by kzalloc().
Also I cannot find where ->is_signed is set.

>
> if (flags & HIST_FIELD_FL_HITCOUNT) {
> hist_field->fn = hist_field_counter;
> @@ -423,6 +432,12 @@ static struct hist_field *create_hist_field(struct ftrace_event_field *field,
> goto out;
> }
>
> + if (flags & HIST_FIELD_FL_TIMESTAMP) {
> + hist_field->fn = hist_field_timestamp;
> + hist_field->size = sizeof(u64);
> + goto out;
> + }
> +
> if (WARN_ON_ONCE(!field))
> goto out;
>

[SNIP]
> @@ -1520,6 +1557,8 @@ static int hist_register_trigger(char *glob, struct event_trigger_ops *ops,
>
> update_cond_flag(file);
>
> + tracing_set_time_stamp_abs(file->tr, true);
> +

Hmm.. does it makes all events using absolute timestamp? Where is it
turned off?

Thanks,
Namhyung

> if (trace_event_trigger_enable_disable(file, 1) < 0) {
> list_del_rcu(&data->list);
> update_cond_flag(file);
> --
> 1.9.3
>