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Subject[PATCH v6 29/37] tracing: Add cpu field for hist triggers
Date
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/histogram.txt | 17 +++++++++++++++++
kernel/trace/trace_events_hist.c | 28 +++++++++++++++++++++++++++-
2 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/Documentation/trace/histogram.txt b/Documentation/trace/histogram.txt
index d1d92ed..cd3ec00 100644
--- a/Documentation/trace/histogram.txt
+++ b/Documentation/trace/histogram.txt
@@ -172,6 +172,23 @@
The examples below provide a more concrete illustration of the
concepts and typical usage patterns discussed above.

+ 'special' event fields
+ ------------------------
+
+ There are a number of 'special event fields' available for use as
+ keys or values in a hist trigger. These look like and behave as if
+ they were actual event fields, but aren't really 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.
+ 'Special' 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 121f7ef..afbfa9c 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -227,6 +227,7 @@ enum hist_field_flags {
HIST_FIELD_FL_VAR = 1 << 12,
HIST_FIELD_FL_EXPR = 1 << 13,
HIST_FIELD_FL_VAR_REF = 1 << 14,
+ HIST_FIELD_FL_CPU = 1 << 15,
};

struct var_defs {
@@ -1177,6 +1178,16 @@ 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 = smp_processor_id();
+
+ return cpu;
+}
+
static struct hist_field *
check_field_for_var_ref(struct hist_field *hist_field,
struct hist_trigger_data *var_data,
@@ -1622,6 +1633,8 @@ 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) {
if (field->system) {
@@ -2125,6 +2138,15 @@ 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;

@@ -2343,7 +2365,9 @@ static struct hist_field *parse_var_ref(struct hist_trigger_data *hist_data,
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 || !field->size) {
field = ERR_PTR(-EINVAL);
@@ -4612,6 +4636,8 @@ 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, "$common_timestamp");
+ else if (hist_field->flags & HIST_FIELD_FL_CPU)
+ seq_puts(m, "cpu");
else if (field_name) {
if (hist_field->flags & HIST_FIELD_FL_VAR_REF)
seq_putc(m, '$');
--
1.9.3
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