[PATCH 4/4] trace: profile all if conditionals
From: Steven Rostedt
Date: Fri Nov 21 2008 - 02:14:54 EST
From: Steven Rostedt <srostedt@xxxxxxxxxx>
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: Steven Rostedt <srostedt@xxxxxxxxxx>
---
include/asm-generic/vmlinux.lds.h | 11 +++++++++-
include/linux/compiler.h | 38 +++++++++++++++++++++++++++++++++++-
kernel/trace/Kconfig | 16 +++++++++++++++
kernel/trace/trace_branch.c | 33 ++++++++++++++++++++++++++++++-
4 files changed, 93 insertions(+), 5 deletions(-)
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 62679ae..30536c3 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -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)); \
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 0628a20..ea7c6be 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -63,8 +63,16 @@ struct ftrace_branch_data {
const char *func;
const char *file;
unsigned line;
- unsigned long correct;
- unsigned long incorrect;
+ union {
+ struct {
+ unsigned long correct;
+ unsigned long incorrect;
+ };
+ struct {
+ unsigned long miss;
+ unsigned long hit;
+ };
+ };
};
/*
@@ -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)
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 7e35487..61e8cca 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -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
diff --git a/kernel/trace/trace_branch.c b/kernel/trace/trace_branch.c
index 142acb3..85792ae 100644
--- a/kernel/trace/trace_branch.c
+++ b/kernel/trace/trace_branch.c
@@ -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;
}
--
1.5.6.5
--
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