Commit 2bcd521a authored by Steven Rostedt's avatar Steven Rostedt Committed by Ingo Molnar
Browse files

trace: profile all if conditionals 



Impact: feature to profile if statements

This patch adds a branch profiler for all if () statements.
The results will be found in:

  /debugfs/tracing/profile_branch

For example:

   miss      hit    %        Function                  File              Line
 ------- ---------  -        --------                  ----              ----
       0        1 100 x86_64_start_reservations      head64.c             127
       0        1 100 copy_bootdata                  head64.c             69
       1        0   0 x86_64_start_kernel            head64.c             111
      32        0   0 set_intr_gate                  desc.h               319
       1        0   0 reserve_ebda_region            head.c               51
       1        0   0 reserve_ebda_region            head.c               47
       0        1 100 reserve_ebda_region            head.c               42
       0        0   X maxcpus                        main.c               165

Miss means the branch was not taken. Hit means the branch was taken.
The percent is the percentage the branch was taken.

This adds a significant amount of overhead and should only be used
by those analyzing their system.

Signed-off-by: default avatarSteven Rostedt <srostedt@redhat.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent bac28bfe

include/asm-generic/vmlinux.lds.h

+10 −1
Original line number Diff line number Diff line
@@ -53,6 +53,14 @@ 
#define LIKELY_PROFILE()

#endif



#ifdef CONFIG_PROFILE_ALL_BRANCHES

#define BRANCH_PROFILE()	VMLINUX_SYMBOL(__start_branch_profile) = .;   \

				*(_ftrace_branch)			      \

				VMLINUX_SYMBOL(__stop_branch_profile) = .;

#else

#define BRANCH_PROFILE()

#endif



/* .data section */

#define DATA_DATA							\

	*(.data)							\
@@ -72,7 +80,8 @@ 
	VMLINUX_SYMBOL(__start___tracepoints) = .;			\

	*(__tracepoints)						\

	VMLINUX_SYMBOL(__stop___tracepoints) = .;			\

	LIKELY_PROFILE()

	LIKELY_PROFILE()		       				\

	BRANCH_PROFILE()



#define RO_DATA(align)							\

	. = ALIGN((align));						\

include/linux/compiler.h

+36 −2
Original line number Diff line number Diff line
@@ -63,9 +63,17 @@ struct ftrace_branch_data { 
	const char *func;

	const char *file;

	unsigned line;

	union {

		struct {

			unsigned long correct;

			unsigned long incorrect;

		};

		struct {

			unsigned long miss;

			unsigned long hit;

		};

	};

};



/*

 * Note: DISABLE_BRANCH_PROFILING can be used by special lowlevel code
@@ -103,6 +111,32 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect); 
# ifndef unlikely

#  define unlikely(x)	(__builtin_constant_p(x) ? !!(x) : __branch_check__(x, 0))

# endif



#ifdef CONFIG_PROFILE_ALL_BRANCHES

/*

 * "Define 'is'", Bill Clinton

 * "Define 'if'", Steven Rostedt

 */

#define if(cond) if (__builtin_constant_p((cond)) ? !!(cond) :		\

	({								\

		int ______r;						\

		static struct ftrace_branch_data			\

			__attribute__((__aligned__(4)))			\

			__attribute__((section("_ftrace_branch")))	\

			______f = {					\

				.func = __func__,			\

				.file = __FILE__,			\

				.line = __LINE__,			\

			};						\

		______r = !!(cond);					\

		if (______r)						\

			______f.hit++;					\

		else							\

			______f.miss++;					\

		______r;						\

	}))

#endif /* CONFIG_PROFILE_ALL_BRANCHES */



#else

# define likely(x)	__builtin_expect(!!(x), 1)

# define unlikely(x)	__builtin_expect(!!(x), 0)

kernel/trace/Kconfig

+16 −0
Original line number Diff line number Diff line
@@ -173,6 +173,22 @@ config TRACE_BRANCH_PROFILING 


	  Say N if unsure.



config PROFILE_ALL_BRANCHES

	bool "Profile all if conditionals"

	depends on TRACE_BRANCH_PROFILING

	help

	  This tracer profiles all branch conditions. Every if ()

	  taken in the kernel is recorded whether it hit or miss.

	  The results will be displayed in:



	  /debugfs/tracing/profile_branch



	  This configuration, when enabled, will impose a great overhead

	  on the system. This should only be enabled when the system

	  is to be analyzed



	  Say N if unsure.



config TRACING_BRANCHES

	bool

	help

kernel/trace/trace_branch.c

+31 −2
Original line number Diff line number Diff line
@@ -185,6 +185,7 @@ EXPORT_SYMBOL(ftrace_likely_update); 
struct ftrace_pointer {

	void		*start;

	void		*stop;

	int		hit;

};



static void *
@@ -223,13 +224,17 @@ static void t_stop(struct seq_file *m, void *p) 


static int t_show(struct seq_file *m, void *v)

{

	struct ftrace_pointer *fp = m->private;

	struct ftrace_branch_data *p = v;

	const char *f;

	long percent;



	if (v == (void *)1) {

		seq_printf(m, " correct incorrect  %% "

			      "       Function                "

		if (fp->hit)

			seq_printf(m, "   miss      hit    %% ");

		else

			seq_printf(m, " correct incorrect  %% ");

		seq_printf(m, "       Function                "

			      "  File              Line\n"

			      " ------- ---------  - "

			      "       --------                "
@@ -243,6 +248,9 @@ static int t_show(struct seq_file *m, void *v) 
		f--;

	f++;



	/*

	 * The miss is overlayed on correct, and hit on incorrect.

	 */

	if (p->correct) {

		percent = p->incorrect * 100;

		percent /= p->correct + p->incorrect;
@@ -284,6 +292,18 @@ static const struct file_operations tracing_branch_fops = { 
	.llseek		= seq_lseek,

};



#ifdef CONFIG_PROFILE_ALL_BRANCHES

extern unsigned long __start_branch_profile[];

extern unsigned long __stop_branch_profile[];



static struct ftrace_pointer ftrace_branch_pos = {

	.start			= __start_branch_profile,

	.stop			= __stop_branch_profile,

	.hit			= 1,

};



#endif /* CONFIG_PROFILE_ALL_BRANCHES */



extern unsigned long __start_annotated_branch_profile[];

extern unsigned long __stop_annotated_branch_profile[];
@@ -306,6 +326,15 @@ static __init int ftrace_branch_init(void) 
		pr_warning("Could not create debugfs "

			   "'profile_annotatet_branch' entry\n");



#ifdef CONFIG_PROFILE_ALL_BRANCHES

	entry = debugfs_create_file("profile_branch", 0444, d_tracer,

				    &ftrace_branch_pos,

				    &tracing_branch_fops);

	if (!entry)

		pr_warning("Could not create debugfs"

			   " 'profile_branch' entry\n");

#endif



	return 0;

}

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