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tracing: Add hist trigger support for stacktraces as keys

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It's often useful to be able to use a stacktrace as a hash key, for
keeping a count of the number of times a particular call path resulted
in a trace event, for instance.  Add a special key named 'stacktrace'
which can be used as key in a 'keys=' param for this purpose:

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

Link: http://lkml.kernel.org/r/87515e90b3785232a874a12156174635a348edb1.1457029949.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>
This commit is contained in:
Tom Zanussi
2016-03-03 12:54:52 -06:00
committed by Steven Rostedt
parent 316961988b
commit 69a0200c2e
2 changed files with 109 additions and 42 deletions
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16
kernel/trace/trace.c
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@@ -3843,14 +3843,14 @@ static const char readme_msg[] =
"\t table using the key(s) and value(s) named, and the value of a\n"
"\t sum called 'hitcount' is incremented. Keys and values\n"
"\t correspond to fields in the event's format description. Keys\n"
"\t can be any field. Compound keys consisting of up to two\n"
"\t fields can be specified by the 'keys' keyword. Values must\n"
"\t correspond to numeric fields. Sort keys consisting of up to\n"
"\t two fields can be specified using the 'sort' keyword. The\n"
"\t sort direction can be modified by appending '.descending' or\n"
"\t '.ascending' to a sort field. The 'size' parameter can be\n"
"\t used to specify more or fewer than the default 2048 entries\n"
"\t for the hashtable size.\n\n"
"\t can be any field, or the special string 'stacktrace'.\n"
"\t Compound keys consisting of up to two fields can be specified\n"
"\t by the 'keys' keyword. Values must correspond to numeric\n"
"\t fields. Sort keys consisting of up to two fields can be\n"
"\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 Reading the 'hist' file for the event will dump the hash\n"
"\t table in its entirety to stdout. The default format used to\n"
"\t display a given field can be modified by appending any of the\n"