[PATCH 20/20] function_graph: Use bitmask to loop on fgraph entry

[Steven Rostedt]

From: "Steven Rostedt (Google)" <rostedt@xxxxxxxxxxx>

Instead of looping through all the elements of fgraph_array[] to see if
there's an gops attached to one and then calling its gops->func(). Create
a fgraph_array_bitmask that sets bits when an index in the array is
reserved (via the simple lru algorithm). Then only the bits set in this
bitmask needs to be looked at where only elements in the array that have
ops registered need to be looked at.

Note, we do not care about races. If a bit is set before the gops is
assigned, it only wastes time looking at the element and ignoring it (as
it did before this bitmask is added).

Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
---
 kernel/trace/fgraph.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index 5e8e13ffcfb6..1aae521e5997 100644
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -173,6 +173,7 @@ DEFINE_STATIC_KEY_FALSE(kill_ftrace_graph);
 int ftrace_graph_active;
 
 static struct fgraph_ops *fgraph_array[FGRAPH_ARRAY_SIZE];
+static unsigned long fgraph_array_bitmask;
 
 /* LRU index table for fgraph_array */
 static int fgraph_lru_table[FGRAPH_ARRAY_SIZE];
@@ -197,6 +198,8 @@ static int fgraph_lru_release_index(int idx)
 
 	fgraph_lru_table[fgraph_lru_last] = idx;
 	fgraph_lru_last = (fgraph_lru_last + 1) % FGRAPH_ARRAY_SIZE;
+
+	clear_bit(idx, &fgraph_array_bitmask);
 	return 0;
 }
 
@@ -211,6 +214,8 @@ static int fgraph_lru_alloc_index(void)
 
 	fgraph_lru_table[fgraph_lru_next] = -1;
 	fgraph_lru_next = (fgraph_lru_next + 1) % FGRAPH_ARRAY_SIZE;
+
+	set_bit(idx, &fgraph_array_bitmask);
 	return idx;
 }
 
@@ -632,7 +637,8 @@ int function_graph_enter(unsigned long ret, unsigned long func,
 	if (offset < 0)
 		goto out;
 
-	for (i = 0; i < FGRAPH_ARRAY_SIZE; i++) {
+	for_each_set_bit(i, &fgraph_array_bitmask,
+			 sizeof(fgraph_array_bitmask) * BITS_PER_BYTE) {
 		struct fgraph_ops *gops = fgraph_array[i];
 		int save_curr_ret_stack;
 
-- 
2.43.0