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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 /kernel
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 'kernel')
-rw-r--r--kernel/trace/fgraph.c17
1 files changed, 3 insertions, 14 deletions
diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index 19028e072cdb..8f4fb328133a 100644
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -7,6 +7,7 @@
*
* Highly modified by Steven Rostedt (VMware).
*/
+#include <linux/jump_label.h>
#include <linux/suspend.h>
#include <linux/ftrace.h>
#include <linux/slab.h>
@@ -23,25 +24,13 @@
#define ASSIGN_OPS_HASH(opsname, val)
#endif
-static bool kill_ftrace_graph;
+DEFINE_STATIC_KEY_FALSE(kill_ftrace_graph);
int ftrace_graph_active;
/* Both enabled by default (can be cleared by function_graph tracer flags */
static bool fgraph_sleep_time = true;
/**
- * 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.
- */
-bool ftrace_graph_is_dead(void)
-{
- return kill_ftrace_graph;
-}
-
-/**
* ftrace_graph_stop - set to permanently disable function graph tracing
*
* In case of an error int function graph tracing, this is called
@@ -51,7 +40,7 @@ bool ftrace_graph_is_dead(void)
*/
void ftrace_graph_stop(void)
{
- kill_ftrace_graph = true;
+ static_branch_enable(&kill_ftrace_graph);
}
/* Add a function return address to the trace stack on thread info.*/