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

Tom Zanussi
2018-12-03T22:22:08Z

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_id
> > x;
> > - 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
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,
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
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.

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($var).
+ */
char *var_str;
struct hist_field *var_ref;
+
+ /*
+ * When a histogram trigger is hit, the values
+ * of any references to variables, including
+ * variables being tracked e.g. onmax($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;