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

Steven Rostedt
2024-06-02T03:37:28Z

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