[PATCH 27/32] tracing: Add cpu field for hist triggers

Tom Zanussi
2017-06-26T22:53:42Z

A common key to use in a histogram is the cpuid - add a new cpu
'synthetic' field for that purpose. This field is named cpu rather
than $cpu or $common_cpu because 'cpu' already exists as a special
filter field and it makes more sense to match that rather than add
another name for the same thing.

Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
---
Documentation/trace/events.txt | 18 ++++++++++++++++++
kernel/trace/trace_events_hist.c | 30 +++++++++++++++++++++++++++---
2 files changed, 45 insertions(+), 3 deletions(-)

diff --git a/Documentation/trace/events.txt b/Documentation/trace/events.txt
index 2cc08d4..9717688 100644
--- a/Documentation/trace/events.txt
+++ b/Documentation/trace/events.txt
@@ -668,6 +668,24 @@ The following commands are supported:
The examples below provide a more concrete illustration of the
concepts and typical usage patterns discussed above.

+ 'synthetic' event fields
+ ------------------------
+
+ There are a number of 'synthetic fields' available for use as keys
+ or values in a hist trigger. These look like and behave as if they
+ were event fields, but aren't actually part of the event's field
+ definition or format file. They are however available for any
+ event, and can be used anywhere an actual event field could be.
+ 'Synthetic' field names are always prefixed with a '$' character to
+ indicate that they're not normal fields (with the exception of
+ 'cpu', for compatibility with existing filter usage):
+
+ $common_timestamp u64 - timestamp (from ring buffer) associated
+ with the event, in nanoseconds. May be
+ modified by .usecs to have timestamps
+ interpreted as microseconds.
+ cpu int - the cpu on which the event occurred.
+

6.2 'hist' trigger examples
---------------------------
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index ab94e2a..904a635 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -224,6 +224,7 @@ enum hist_field_flags {
HIST_FIELD_FL_VAR_ONLY = 8192,
HIST_FIELD_FL_EXPR = 16384,
HIST_FIELD_FL_VAR_REF = 32768,
+ HIST_FIELD_FL_CPU = 65536,
};

struct hist_trigger_attrs {
@@ -1081,6 +1082,16 @@ static u64 hist_field_timestamp(struct hist_field *hist_field,
return ts;
}

+static u64 hist_field_cpu(struct hist_field *hist_field,
+ struct tracing_map_elt *elt,
+ struct ring_buffer_event *rbe,
+ void *event)
+{
+ int cpu = raw_smp_processor_id();
+
+ return cpu;
+}
+
static struct hist_field *check_var_ref(struct hist_field *hist_field,
struct hist_trigger_data *var_data,
unsigned int var_idx)
@@ -1407,6 +1418,8 @@ static const char *hist_field_name(struct hist_field *field,
field_name = hist_field_name(field->operands[0], ++level);
else if (field->flags & HIST_FIELD_FL_TIMESTAMP)
field_name = "$common_timestamp";
+ else if (field->flags & HIST_FIELD_FL_CPU)
+ field_name = "cpu";
else if (field->flags & HIST_FIELD_FL_EXPR ||
field->flags & HIST_FIELD_FL_VAR_REF)
field_name = field->name;
@@ -1848,6 +1861,15 @@ static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data,
goto out;
}

+ if (flags & HIST_FIELD_FL_CPU) {
+ hist_field->fn = hist_field_cpu;
+ hist_field->size = sizeof(int);
+ hist_field->type = kstrdup("int", GFP_KERNEL);
+ if (!hist_field->type)
+ goto free;
+ goto out;
+ }
+
if (WARN_ON_ONCE(!field))
goto out;

@@ -1980,7 +2002,9 @@ static struct hist_field *parse_var_ref(char *system, char *event_name,
hist_data->enable_timestamps = true;
if (*flags & HIST_FIELD_FL_TIMESTAMP_USECS)
hist_data->attrs->ts_in_usecs = true;
- } else {
+ } else if (strcmp(field_name, "cpu") == 0)
+ *flags |= HIST_FIELD_FL_CPU;
+ else {
field = trace_find_event_field(file->event_call, field_name);
if (!field)
return ERR_PTR(-EINVAL);
@@ -3019,7 +3043,6 @@ static int onmatch_create(struct hist_trigger_data *hist_data,
goto out;
}
}
-
if (param[0] == '$')
hist_field = onmatch_find_var(hist_data, data, system,
event_name, param);
@@ -3034,7 +3057,6 @@ static int onmatch_create(struct hist_trigger_data *hist_data,
ret = -EINVAL;
goto out;
}
-
if (check_synth_field(event, hist_field, field_pos) == 0) {
var_ref = create_var_ref(hist_field);
if (!var_ref) {
@@ -4128,6 +4150,8 @@ static void hist_field_print(struct seq_file *m, struct hist_field *hist_field)

if (hist_field->flags & HIST_FIELD_FL_TIMESTAMP)
seq_puts(m, "$common_timestamp");
+ else if (hist_field->flags & HIST_FIELD_FL_CPU)
+ seq_puts(m, "cpu");
else if (field_name)
seq_printf(m, "%s", field_name);

--
1.9.3