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authorChristophe Leroy <christophe.leroy@csgroup.eu>2022-03-30 09:00:19 +0200
committerSteven Rostedt (Google) <rostedt@goodmis.org>2022-04-02 08:40:09 -0400
commit18bfee3216fa6f28d55ebf88d824a539d2bec3c7 (patch)
tree57fb3d2d8b7a9b0620a51de3dbb8134fb9291db8 /include
parentfcbf591cedbd44d82d7765b3c7e261858108593f (diff)
ftrace: Make ftrace_graph_is_dead() a static branch
ftrace_graph_is_dead() is used on hot paths, it just reads a variable in memory and is not worth suffering function call constraints. For instance, at entry of prepare_ftrace_return(), inlining it avoids saving prepare_ftrace_return() parameters to stack and restoring them after calling ftrace_graph_is_dead(). While at it using a static branch is even more performant and is rather well adapted considering that the returned value will almost never change. Inline ftrace_graph_is_dead() and replace 'kill_ftrace_graph' bool by a static branch. The performance improvement is noticeable. Link: https://lkml.kernel.org/r/e0411a6a0ed3eafff0ad2bc9cd4b0e202b4617df.1648623570.git.christophe.leroy@csgroup.eu Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Diffstat (limited to 'include')
-rw-r--r--include/linux/ftrace.h16
1 files changed, 15 insertions, 1 deletions
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 37b619185ec9..f15a4b76cbfc 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -9,6 +9,7 @@
#include <linux/trace_recursion.h>
#include <linux/trace_clock.h>
+#include <linux/jump_label.h>
#include <linux/kallsyms.h>
#include <linux/linkage.h>
#include <linux/bitops.h>
@@ -1015,7 +1016,20 @@ unsigned long ftrace_graph_ret_addr(struct task_struct *task, int *idx,
extern int register_ftrace_graph(struct fgraph_ops *ops);
extern void unregister_ftrace_graph(struct fgraph_ops *ops);
-extern bool ftrace_graph_is_dead(void);
+/**
+ * ftrace_graph_is_dead - returns true if ftrace_graph_stop() was called
+ *
+ * ftrace_graph_stop() is called when a severe error is detected in
+ * the function graph tracing. This function is called by the critical
+ * paths of function graph to keep those paths from doing any more harm.
+ */
+DECLARE_STATIC_KEY_FALSE(kill_ftrace_graph);
+
+static inline bool ftrace_graph_is_dead(void)
+{
+ return static_branch_unlikely(&kill_ftrace_graph);
+}
+
extern void ftrace_graph_stop(void);
/* The current handlers in use */