[PATCH v2 25/27] function_graph: Use static_call and branch to optimize return function

[Steven Rostedt]

From: "Steven Rostedt (Google)" <rost...@goodmis.org>

In most cases function graph is used by a single user. Instead of calling
a loop to call function graph callbacks in this case, call the function
return callback directly.

Use the static_key that is set when the function graph tracer has less
than 2 callbacks registered. It will do the direct call in that case, and
will do the loop over all callers when there are 2 or more callbacks
registered.

Signed-off-by: Steven Rostedt (Google) <rost...@goodmis.org>
---
 kernel/trace/fgraph.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index 7c3b0261b1bb..4bf91eebbb08 100644
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -514,6 +514,7 @@ static struct fgraph_ops fgraph_stub = {
 
 static struct fgraph_ops *fgraph_direct_gops = &fgraph_stub;
 DEFINE_STATIC_CALL(fgraph_func, ftrace_graph_entry_stub);
+DEFINE_STATIC_CALL(fgraph_retfunc, ftrace_graph_ret_stub);
 DEFINE_STATIC_KEY_TRUE(fgraph_do_direct);
 
 /**
@@ -808,13 +809,21 @@ static unsigned long __ftrace_return_to_handler(struct 
fgraph_ret_regs *ret_regs
 
        bitmap = get_bitmap_bits(current, offset);
 
-       for_each_set_bit(i, &bitmap, sizeof(bitmap) * BITS_PER_BYTE) {
-               struct fgraph_ops *gops = fgraph_array[i];
+#ifdef CONFIG_HAVE_STATIC_CALL
+       if (static_branch_likely(&fgraph_do_direct)) {
+               if (test_bit(fgraph_direct_gops->idx, &bitmap))
+                       static_call(fgraph_retfunc)(&trace, fgraph_direct_gops);
+       } else
+#endif
+       {
+               for_each_set_bit(i, &bitmap, sizeof(bitmap) * BITS_PER_BYTE) {
+                       struct fgraph_ops *gops = fgraph_array[i];
 
-               if (gops == &fgraph_stub)
-                       continue;
+                       if (gops == &fgraph_stub)
+                               continue;
 
-               gops->retfunc(&trace, gops);
+                       gops->retfunc(&trace, gops);
+               }
        }
 
        /*
@@ -1232,17 +1241,20 @@ static void init_task_vars(int idx)
 static void ftrace_graph_enable_direct(bool enable_branch)
 {
        trace_func_graph_ent_t func = NULL;
+       trace_func_graph_ret_t retfunc = NULL;
        int i;
 
        for_each_set_bit(i, &fgraph_array_bitmask,
                         sizeof(fgraph_array_bitmask) * BITS_PER_BYTE) {
                func = fgraph_array[i]->entryfunc;
+               retfunc = fgraph_array[i]->retfunc;
                fgraph_direct_gops = fgraph_array[i];
         }
        if (WARN_ON_ONCE(!func))
                return;
 
        static_call_update(fgraph_func, func);
+       static_call_update(fgraph_retfunc, retfunc);
        if (enable_branch)
                static_branch_disable(&fgraph_do_direct);
 }
@@ -1252,6 +1264,7 @@ static void ftrace_graph_disable_direct(bool 
disable_branch)
        if (disable_branch)
                static_branch_disable(&fgraph_do_direct);
        static_call_update(fgraph_func, ftrace_graph_entry_stub);
+       static_call_update(fgraph_retfunc, ftrace_graph_ret_stub);
        fgraph_direct_gops = &fgraph_stub;
 }
 
-- 
2.43.0