tracing: Add support for named hist triggers

Allow users to define 'named' hist triggers.  All triggers created
with the same 'name=xxx' option will update the same shared histogram
data.

This expands the hist trigger syntax from this:

    # echo hist:keys=xxx ... [ if filter] > event/trigger

to this:

    # echo hist:name=xxx:keys=xxx ... [ if filter] > event/trigger

Named histograms must use a 'compatible' set of keys and values, which
means each event added to a set of named triggers must have the same
names and types.

Reading the 'hist' file of any of the participating events will
produce the same output as any other participating event, which is to
be expected since they share the same data.

Link: http://lkml.kernel.org/r/1dbc84ee3322a75daaf5b3ef1d0cc0a2fb682fc7.1457029949.git.tom.zanussi@linux.intel.com

Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Tested-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 10 insertions, 4 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index e89b2ed76d2d..4e342d354c12 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3842,6 +3842,7 @@ static const char readme_msg[] =
 	"\t            [:sort=<field1[,field2,...]>]\n"
 	"\t            [:size=#entries]\n"
 	"\t            [:pause][:continue][:clear]\n"
+	"\t            [:name=histname1]\n"
 	"\t            [if <filter>]\n\n"
 	"\t    When a matching event is hit, an entry is added to a hash\n"
 	"\t    table using the key(s) and value(s) named, and the value of a\n"
@@ -3854,13 +3855,18 @@ static const char readme_msg[] =
 	"\t    specified using the 'sort' keyword.  The sort direction can\n"
 	"\t    be modified by appending '.descending' or '.ascending' to a\n"
 	"\t    sort field.  The 'size' parameter can be used to specify more\n"
-	"\t    or fewer than the default 2048 entries for the hashtable size.\n\n"
+	"\t    or fewer than the default 2048 entries for the hashtable size.\n"
+	"\t    If a hist trigger is given a name using the 'name' parameter,\n"
+	"\t    its histogram data will be shared with other triggers of the\n"
+	"\t    same name, and trigger hits will update this common data.\n\n"
 	"\t    Reading the 'hist' file for the event will dump the hash\n"
 	"\t    table in its entirety to stdout.  If there are multiple hist\n"
 	"\t    triggers attached to an event, there will be a table for each\n"
-	"\t    trigger in the output.  The default format used to display a\n"
-	"\t    given field can be modified by appending any of the following\n"
-	"\t    modifiers to the field name, as applicable:\n\n"
+	"\t    trigger in the output.  The table displayed for a named\n"
+	"\t    trigger will be the same as any other instance having the\n"
+	"\t    same name.  The default format used to display a given field\n"
+	"\t    can be modified by appending any of the following modifiers\n"
+	"\t    to the field name, as applicable:\n\n"
 	"\t            .hex        display a number as a hex value\n"
 	"\t            .sym        display an address as a symbol\n"
 	"\t            .sym-offset display an address as a symbol and offset\n"