Commit 18bfee32 authored by Christophe Leroy's avatar Christophe Leroy Committed by Steven Rostedt (Google)

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.euSigned-off-by: default avatarChristophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent fcbf591c
...@@ -9,6 +9,7 @@ ...@@ -9,6 +9,7 @@
#include <linux/trace_recursion.h> #include <linux/trace_recursion.h>
#include <linux/trace_clock.h> #include <linux/trace_clock.h>
#include <linux/jump_label.h>
#include <linux/kallsyms.h> #include <linux/kallsyms.h>
#include <linux/linkage.h> #include <linux/linkage.h>
#include <linux/bitops.h> #include <linux/bitops.h>
...@@ -1015,7 +1016,20 @@ unsigned long ftrace_graph_ret_addr(struct task_struct *task, int *idx, ...@@ -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 int register_ftrace_graph(struct fgraph_ops *ops);
extern void unregister_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); extern void ftrace_graph_stop(void);
/* The current handlers in use */ /* The current handlers in use */
......
...@@ -7,6 +7,7 @@ ...@@ -7,6 +7,7 @@
* *
* Highly modified by Steven Rostedt (VMware). * Highly modified by Steven Rostedt (VMware).
*/ */
#include <linux/jump_label.h>
#include <linux/suspend.h> #include <linux/suspend.h>
#include <linux/ftrace.h> #include <linux/ftrace.h>
#include <linux/slab.h> #include <linux/slab.h>
...@@ -23,24 +24,12 @@ ...@@ -23,24 +24,12 @@
#define ASSIGN_OPS_HASH(opsname, val) #define ASSIGN_OPS_HASH(opsname, val)
#endif #endif
static bool kill_ftrace_graph; DEFINE_STATIC_KEY_FALSE(kill_ftrace_graph);
int ftrace_graph_active; int ftrace_graph_active;
/* Both enabled by default (can be cleared by function_graph tracer flags */ /* Both enabled by default (can be cleared by function_graph tracer flags */
static bool fgraph_sleep_time = true; 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 * ftrace_graph_stop - set to permanently disable function graph tracing
* *
...@@ -51,7 +40,7 @@ bool ftrace_graph_is_dead(void) ...@@ -51,7 +40,7 @@ bool ftrace_graph_is_dead(void)
*/ */
void ftrace_graph_stop(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.*/ /* Add a function return address to the trace stack on thread info.*/
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment