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authorSteven Rostedt (VMware) <rostedt@goodmis.org>2019-02-11 15:00:48 -0500
committerSteven Rostedt (VMware) <rostedt@goodmis.org>2019-02-15 13:10:09 -0500
commitf79b3f338564e7674dbe6375bcf685c2ba483efe (patch)
tree481aa4a5340b5c1f3d9a167f06fce036ba08fbc7
parent85acbb21b9310043692cf18b1fd14067b5a25ccd (diff)
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>
-rw-r--r--Documentation/trace/ftrace.rst38
-rw-r--r--kernel/trace/ftrace.c30
-rw-r--r--kernel/trace/trace.h1
-rw-r--r--kernel/trace/trace_events_filter.c5
4 files changed, 74 insertions, 0 deletions
diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst
index 6ce2763a2a3e..7c5e6d6ab5d1 100644
--- a/Documentation/trace/ftrace.rst
+++ b/Documentation/trace/ftrace.rst
@@ -233,6 +233,12 @@ of ftrace. Here is a list of some of the key files:
This interface also allows for commands to be used. See the
"Filter commands" section for more details.
+ As a speed up, since processing strings can't be quite expensive
+ and requires a check of all functions registered to tracing, instead
+ an index can be written into this file. A number (starting with "1")
+ written will instead select the same corresponding at the line position
+ of the "available_filter_functions" file.
+
set_ftrace_notrace:
This has an effect opposite to that of
@@ -2835,6 +2841,38 @@ Produces::
We can see that there's no more lock or preempt tracing.
+Selecting function filters via index
+------------------------------------
+
+Because processing of strings is expensive (the address of the function
+needs to be looked up before comparing to the string being passed in),
+an index can be used as well to enable functions. This is useful in the
+case of setting thousands of specific functions at a time. By passing
+in a list of numbers, no string processing will occur. Instead, the function
+at the specific location in the internal array (which corresponds to the
+functions in the "available_filter_functions" file), is selected.
+
+::
+
+ # echo 1 > set_ftrace_filter
+
+Will select the first function listed in "available_filter_functions"
+
+::
+
+ # head -1 available_filter_functions
+ trace_initcall_finish_cb
+
+ # cat set_ftrace_filter
+ trace_initcall_finish_cb
+
+ # head -50 available_filter_functions | tail -1
+ x86_pmu_commit_txn
+
+ # echo 1 50 > set_ftrace_filter
+ # cat set_ftrace_filter
+ trace_initcall_finish_cb
+ x86_pmu_commit_txn
Dynamic ftrace with the function graph tracer
---------------------------------------------
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index aac7847c0214..fa79323331b2 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -3702,6 +3702,31 @@ enter_record(struct ftrace_hash *hash, struct dyn_ftrace *rec, int clear_filter)
}
static int
+add_rec_by_index(struct ftrace_hash *hash, struct ftrace_glob *func_g,
+ int clear_filter)
+{
+ long index = simple_strtoul(func_g->search, NULL, 0);
+ struct ftrace_page *pg;
+ struct dyn_ftrace *rec;
+
+ /* The index starts at 1 */
+ if (--index < 0)
+ return 0;
+
+ do_for_each_ftrace_rec(pg, rec) {
+ if (pg->index <= index) {
+ index -= pg->index;
+ /* this is a double loop, break goes to the next page */
+ break;
+ }
+ rec = &pg->records[index];
+ enter_record(hash, rec, clear_filter);
+ return 1;
+ } while_for_each_ftrace_rec();
+ return 0;
+}
+
+static int
ftrace_match_record(struct dyn_ftrace *rec, struct ftrace_glob *func_g,
struct ftrace_glob *mod_g, int exclude_mod)
{
@@ -3769,6 +3794,11 @@ match_records(struct ftrace_hash *hash, char *func, int len, char *mod)
if (unlikely(ftrace_disabled))
goto out_unlock;
+ if (func_g.type == MATCH_INDEX) {
+ found = add_rec_by_index(hash, &func_g, clear_filter);
+ goto out_unlock;
+ }
+
do_for_each_ftrace_rec(pg, rec) {
if (rec->flags & FTRACE_FL_DISABLED)
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index a34fa5e76abb..ae7df090b93e 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1459,6 +1459,7 @@ enum regex_type {
MATCH_MIDDLE_ONLY,
MATCH_END_ONLY,
MATCH_GLOB,
+ MATCH_INDEX,
};
struct regex {
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;