tracing: Add cpu field for hist triggers

A common key to use in a histogram is the cpuid - add a new cpu
'synthetic' field named 'cpu' for that purpose.

Link: http://lkml.kernel.org/r/89537645bfc957e0d76e2cacf5f0ada88691a6cc.1516069914.git.tom.zanussi@linux.intel.com

Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

Documentation/trace/histogram.txt

@@ -172,6 +172,21 @@
   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.
+  They are:
+
+    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
 ---------------------------

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 {
@@ -1164,6 +1165,16 @@ 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,
@@ -1602,6 +1613,8 @@ 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) {
@@ -2109,6 +2122,15 @@ 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("unsigned int", GFP_KERNEL);
+		if (!hist_field->type)
+			goto free;
+		goto out;
+	}
+
 	if (WARN_ON_ONCE(!field))
 		goto out;
 
@@ -2345,7 +2367,9 @@ parse_field(struct hist_trigger_data *hist_data, struct trace_event_file *file,
 		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);
@@ -4619,6 +4643,8 @@ 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, '$');