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Subject[PATCH v3 7/7] dynamic_debug: add jump label support
Date
Although dynamic debug is often only used for debug builds, sometimes its
enabled for production builds as well. Minimize its impact by using jump
labels. This reduces the text section by 7000+ bytes in the kernel image
below. It does increase data, but this should only be referenced when
changing the direction of the branches, and hence usually not in cache.

text data bss dec hex filename
8194852 4879776 925696 14000324 d5a0c4 vmlinux.pre
8187337 4960224 925696 14073257 d6bda9 vmlinux.post

Signed-off-by: Jason Baron <jbaron@akamai.com>
---
include/linux/dynamic_debug.h | 60 ++++++++++++++++++++++++++++++++++++++-----
lib/dynamic_debug.c | 7 +++++
2 files changed, 61 insertions(+), 6 deletions(-)

diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index 4f1bbc68cd1b..546d68057e3b 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -1,6 +1,10 @@
#ifndef _DYNAMIC_DEBUG_H
#define _DYNAMIC_DEBUG_H

+#if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)
+#include <linux/jump_label.h>
+#endif
+
/*
* An instance of this structure is created in a special
* ELF section at every dynamic debug callsite. At runtime,
@@ -33,6 +37,12 @@ struct _ddebug {
#define _DPRINTK_FLAGS_DEFAULT 0
#endif
unsigned int flags:8;
+#ifdef HAVE_JUMP_LABEL
+ union {
+ struct static_key_true dd_key_true;
+ struct static_key_false dd_key_false;
+ } key;
+#endif
} __attribute__((aligned(8)));


@@ -60,7 +70,7 @@ void __dynamic_netdev_dbg(struct _ddebug *descriptor,
const struct net_device *dev,
const char *fmt, ...);

-#define DEFINE_DYNAMIC_DEBUG_METADATA(name, fmt) \
+#define DEFINE_DYNAMIC_DEBUG_METADATA_KEY(name, fmt, key, init) \
static struct _ddebug __aligned(8) \
__attribute__((section("__verbose"))) name = { \
.modname = KBUILD_MODNAME, \
@@ -68,13 +78,51 @@ void __dynamic_netdev_dbg(struct _ddebug *descriptor,
.filename = __FILE__, \
.format = (fmt), \
.lineno = __LINE__, \
- .flags = _DPRINTK_FLAGS_DEFAULT, \
+ .flags = _DPRINTK_FLAGS_DEFAULT, \
+ dd_key_init(key, init) \
}

+#ifdef HAVE_JUMP_LABEL
+
+#define dd_key_init(key, init) key = (init)
+
+#ifdef DEBUG
+#define DEFINE_DYNAMIC_DEBUG_METADATA(name, fmt) \
+ DEFINE_DYNAMIC_DEBUG_METADATA_KEY(name, fmt, .key.dd_key_true, \
+ (STATIC_KEY_TRUE_INIT))
+
+#define DYNAMIC_DEBUG_BRANCH(descriptor) \
+ static_branch_likely(&descriptor.key.dd_key_true)
+#else
+#define DEFINE_DYNAMIC_DEBUG_METADATA(name, fmt) \
+ DEFINE_DYNAMIC_DEBUG_METADATA_KEY(name, fmt, .key.dd_key_false, \
+ (STATIC_KEY_FALSE_INIT))
+
+#define DYNAMIC_DEBUG_BRANCH(descriptor) \
+ static_branch_unlikely(&descriptor.key.dd_key_false)
+#endif
+
+#else
+
+#define dd_key_init(key, init)
+
+#define DEFINE_DYNAMIC_DEBUG_METADATA(name, fmt) \
+ DEFINE_DYNAMIC_DEBUG_METADATA_KEY(name, fmt, 0, 0)
+
+#ifdef DEBUG
+#define DYNAMIC_DEBUG_BRANCH(descriptor) \
+ likely(descriptor.flags & _DPRINTK_FLAGS_PRINT)
+#else
+#define DYNAMIC_DEBUG_BRANCH(descriptor) \
+ unlikely(descriptor.flags & _DPRINTK_FLAGS_PRINT)
+#endif
+
+#endif
+
#define dynamic_pr_debug(fmt, ...) \
do { \
DEFINE_DYNAMIC_DEBUG_METADATA(descriptor, fmt); \
- if (unlikely(descriptor.flags & _DPRINTK_FLAGS_PRINT)) \
+ if (DYNAMIC_DEBUG_BRANCH(descriptor)) \
__dynamic_pr_debug(&descriptor, pr_fmt(fmt), \
##__VA_ARGS__); \
} while (0)
@@ -82,7 +130,7 @@ do { \
#define dynamic_dev_dbg(dev, fmt, ...) \
do { \
DEFINE_DYNAMIC_DEBUG_METADATA(descriptor, fmt); \
- if (unlikely(descriptor.flags & _DPRINTK_FLAGS_PRINT)) \
+ if (DYNAMIC_DEBUG_BRANCH(descriptor)) \
__dynamic_dev_dbg(&descriptor, dev, fmt, \
##__VA_ARGS__); \
} while (0)
@@ -90,7 +138,7 @@ do { \
#define dynamic_netdev_dbg(dev, fmt, ...) \
do { \
DEFINE_DYNAMIC_DEBUG_METADATA(descriptor, fmt); \
- if (unlikely(descriptor.flags & _DPRINTK_FLAGS_PRINT)) \
+ if (DYNAMIC_DEBUG_BRANCH(descriptor)) \
__dynamic_netdev_dbg(&descriptor, dev, fmt, \
##__VA_ARGS__); \
} while (0)
@@ -100,7 +148,7 @@ do { \
do { \
DEFINE_DYNAMIC_DEBUG_METADATA(descriptor, \
__builtin_constant_p(prefix_str) ? prefix_str : "hexdump");\
- if (unlikely(descriptor.flags & _DPRINTK_FLAGS_PRINT)) \
+ if (DYNAMIC_DEBUG_BRANCH(descriptor)) \
print_hex_dump(KERN_DEBUG, prefix_str, \
prefix_type, rowsize, groupsize, \
buf, len, ascii); \
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index fe42b6ec3f0c..da796e2dc4f5 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -188,6 +188,13 @@ static int ddebug_change(const struct ddebug_query *query,
newflags = (dp->flags & mask) | flags;
if (newflags == dp->flags)
continue;
+#ifdef HAVE_JUMP_LABEL
+ if (dp->flags & _DPRINTK_FLAGS_PRINT) {
+ if (!(flags & _DPRINTK_FLAGS_PRINT))
+ static_branch_disable(&dp->key.dd_key_true);
+ } else if (flags & _DPRINTK_FLAGS_PRINT)
+ static_branch_enable(&dp->key.dd_key_true);
+#endif
dp->flags = newflags;
vpr_info("changed %s:%d [%s]%s =%s\n",
trim_prefix(dp->filename), dp->lineno,
--
2.6.1
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