Re: [PATCH v7 05/16] tracing: Generalize hist trigger onmax and save action

Namhyung Kim
2018-12-04T07:25:53Z

On Mon, Dec 03, 2018 at 04:22:02PM -0600, Tom Zanussi wrote:
> Hi Namhyung,
>
> On Fri, 2018-11-23 at 11:50 +0900, Namhyung Kim wrote:
> > Hi Tom,
> >
> > On Wed, Nov 14, 2018 at 02:18:02PM -0600, Tom Zanussi wrote:
> > > From: Tom Zanussi <tom.zanussi@linux.intel.com>
> > >
>
> [snip]
>
> > >
> enum handler_id {
> > > HANDLER_ONMATCH = 1,
> > > HANDLER_ONMAX,
> > > @@ -349,14 +358,18 @@ struct action_data {
> > >
> > > struct {
> > > char *var_str;
> > > - unsigned int max_var_ref_idx;
> > > - struct hist_field *max_var;
> > > - struct hist_field *var;
> > > - } onmax;
> > > + struct hist_field *var_ref;
> > > + unsigned int var_ref_idx;
> >
> > I have a question. It's confusing for me there are many indexes for
> > a
> > variable (ref). The hist_field already has var.idx, var_idx and
> > var_ref_idx in it. But you also added an external var_ref_idx along
> > with the var_ref. Also I see another var_ref_idx in the action data.
> > Is all that really needed? Could you please add some comment then?
> >
>
> Below is a patch with some comments I'll merge into the next version
> that I hope will help make things more clear. Basically, the
> hist_field.var_idx isn't used so I've removed it and therefore that

Thanks!

> source of confusion, while var.idx is the variable's unique 'handle' in
> the tracing_map, used when getting and setting the variable. And then
> there are the several versions of var_ref_idx used for different
> purposes depending on the context, but all of them are indices into the
> array of variable values collected when a trigger is hit. For example,

So IIUC field->var_ref_idx is an index to the val_ref_vals array,
right? Then if we keep the all hist_fields we don't need to have a
separate var_ref_idx IMHO.

> the var_ref_idx defined inside track_data is the index that points to
> the tracked var value, which the action can use directly, and the

I guess the track_data.var_ref_idx is always same as the
track_data.track_var.var_ref_idx, no? If so we can get rid of it.

> var_ref_idx alongside the synth fields in action_data is the index of
> the first param used when generating a synthetic event, and so on.

For synth event, we have hist_data->synth_var_refs[] but it's not
passed to trace_synth() so no way to know original var_ref_idx and I'm
ok with having action_data.var_ref_idx.

But I don't see where hist_data->synth_var_refs is used other than
find_var_ref(). And for that purpose, I guess it's more efficient to
use hist_data->var_refs[] so that we can remove synth_var_refs.

>
> Tom
>
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index 818944391d97..5310ef73f023 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -39,6 +39,16 @@ enum field_op_id {
> FIELD_OP_UNARY_MINUS,
> };
>
> +/*
> + * A hist_var (histogram variable) contains variable information for
> + * hist_fields having the HIST_FIELD_FL_VAR or HIST_FIELD_FL_VAR_REF
> + * flag set. A hist_var has a variable name e.g. ts0, and is
> + * associated with a given histogram trigger, as specified by
> + * hist_data. The hist_var idx is the unique index assigned to the
> + * variable by the hist trigger's tracing_map. The idx is what is
> + * used to set a variable's value and, by a variable reference, to
> + * retrieve it.
> + */
> struct hist_var {
> char *name;
> struct hist_trigger_data *hist_data;
> @@ -60,7 +70,15 @@ struct hist_field {
> char *system;
> char *event_name;
> char *name;
> - unsigned int var_idx;
> +
> + /*
> + * When a histogram trigger is hit, if it has any references
> + * to variables, the values of those variables are collected
> + * into a var_ref_vals array by resolve_var_refs(). The
> + * current value of each variable is read from the tracing_map
> + * using the hist field's hist_var.idx and entered into the
> + * var_ref_idx entry i.e. var_ref_vals[var_ref_idx].
> + */
> unsigned int var_ref_idx;
> bool read_once;
> };
> @@ -350,6 +368,14 @@ struct action_data {
> unsigned int n_params;
> char *params[SYNTH_FIELDS_MAX];
>
> + /*
> + * When a histogram trigger is hit, the values of any
> + * references to variables, including variables being passed
> + * as parameters to synthetic events, are collected into a
> + * var_ref_vals array. This var_ref_idx is the index of the
> + * first param in the array to be passed to the synthetic
> + * event invocation.
> + */
> unsigned int var_ref_idx;
> struct synth_event *synth_event;
> bool use_trace_keyword;
> @@ -362,10 +388,29 @@ struct action_data {
> } match_data;
>
> struct {
> + /*
> + * var_str and var_ref refer to the variable
> + * being tracked e.g onmax($var).
> + */
> char *var_str;

Can it be different from var_ref->var.name?

Thanks,
Namhyung

> struct hist_field *var_ref;
> +
> + /*
> + * When a histogram trigger is hit, the values
> + * of any references to variables, including
> + * variables being tracked e.g. onmax($var),
> + * are collected into a var_ref_vals array.
> + * This var_ref_idx is the index of the
> + * tracked var value in var_ref_vals, which
> + * the action can make use of directly.
> + */
> unsigned int var_ref_idx;
>
> + /*
> + * This track_var contains the 'invisible'
> + * tracking variable created to keep the
> + * current e.g. max value.
> + */
> struct hist_field *track_var;
>
> check_track_val_fn_t check_val;