ftrace: Allow enabling of filters via index of available_filter_functions

Enabling of large number of functions by echoing in a large subset of the
functions in available_filter_functions can take a very long time. The
process requires testing all functions registered by the function tracer
(which is in the 10s of thousands), and doing a kallsyms lookup to convert
the ip address into a name, then comparing that name with the string passed
in.

When a function causes the function tracer to crash the system, a binary
bisect of the available_filter_functions can be done to find the culprit.
But this requires passing in half of the functions in
available_filter_functions over and over again, which makes it basically a
O(n^2) operation. With 40,000 functions, that ends up bing 1,600,000,000
opertions! And enabling this can take over 20 minutes.

As a quick speed up, if a number is passed into one of the filter files,
instead of doing a search, it just enables the function at the corresponding
line of the available_filter_functions file. That is:

 # echo 50 > set_ftrace_filter
 # cat set_ftrace_filter
 x86_pmu_commit_txn

 # head -50 available_filter_functions | tail -1
 x86_pmu_commit_txn

This allows setting of half the available_filter_functions to take place in
less than a second!

 # time seq 20000 > set_ftrace_filter
 real    0m0.042s
 user    0m0.005s
 sys     0m0.015s

 # wc -l set_ftrace_filter
 20000 set_ftrace_filter

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index f052ecb085e9..ade606c33231 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -825,6 +825,9 @@ enum regex_type filter_parse_regex(char *buff, int len, char **search, int *not)
 
 	*search = buff;
 
+	if (isdigit(buff[0]))
+		return MATCH_INDEX;
+
 	for (i = 0; i < len; i++) {
 		if (buff[i] == '*') {
 			if (!i) {
@@ -862,6 +865,8 @@ static void filter_build_regex(struct filter_pred *pred)
 	}
 
 	switch (type) {
+	/* MATCH_INDEX should not happen, but if it does, match full */
+	case MATCH_INDEX:
 	case MATCH_FULL:
 		r->match = regex_match_full;
 		break;