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Subject[PATCH] Profile likely/unlikely macros
This patch adds a very lightweight profiling feature to the
likely/unlikely macros. It should work in all contexts including
NMI, and during boot. The patch is for 2.6.17-rc2 .

It has a /proc/likely_prof interface which outputs something like
the following,

Likely Profiling Results
--------------------------------------------------------------------
[+- ] Type | # True | # False | Function:Filename@Line
unlikely | 0| 3 tcp_sacktag_write_queue()@:net/ipv4/tcp_input.c@1215
unlikely | 0| 3 tcp_sacktag_write_queue()@:net/ipv4/tcp_input.c@1214
unlikely | 0| 3 tcp_sacktag_write_queue()@:net/ipv4/tcp_input.c@1213
+unlikely | 5050| 0 do_sys_vm86()@:arch/i386/kernel/vm86.c@314
unlikely | 0| 5050 do_sys_vm86()@:arch/i386/kernel/vm86.c@305
+unlikely | 10100| 0 load_esp0()@:include/asm/processor.h@498
+unlikely | 10100| 0 load_esp0()@:include/asm/processor.h@498
-likely | 0| 1945 audit_free()@:kernel/auditsc.c@715
You can identify which statments are miss labeled from the + or - in front .

Signed-Off-By: Daniel Walker <dwalker@mvista.com>

Index: linux-2.6.16/include/linux/compiler.h
===================================================================
--- linux-2.6.16.orig/include/linux/compiler.h
+++ linux-2.6.16/include/linux/compiler.h
@@ -53,14 +53,44 @@ extern void __chk_io_ptr(void __iomem *)
# include <linux/compiler-intel.h>
#endif

+#ifdef CONFIG_PROFILE_LIKELY
+struct likeliness {
+ const char *func;
+ char *file;
+ int line;
+ int type;
+ unsigned int count[2];
+ struct likeliness *next;
+};
+
+extern int do_check_likely(struct likeliness *likeliness, int exp);
+
+# define LIKELY_UNSEEN 4
+
+# define __check_likely(exp, is_likely) \
+ ({ \
+ static __attribute__((__section__(".likely.data"))) \
+ struct likeliness likeliness = { \
+ .func = __func__, \
+ .file = __FILE__, \
+ .line = __LINE__, \
+ .type = is_likely | LIKELY_UNSEEN, \
+ }; \
+ do_check_likely(&likeliness, !!(exp)); \
+ })
+
+# define likely(x) __check_likely(x, 1)
+# define unlikely(x) __check_likely(x, 0)
+#else
/*
* Generic compiler-dependent macros required for kernel
* build go below this comment. Actual compiler/compiler version
* specific implementations come from the above header files
*/

-#define likely(x) __builtin_expect(!!(x), 1)
-#define unlikely(x) __builtin_expect(!!(x), 0)
+# define likely(x) __builtin_expect(!!(x), 1)
+# define unlikely(x) __builtin_expect(!!(x), 0)
+#endif

/* Optimization barrier */
#ifndef barrier
Index: linux-2.6.16/lib/Kconfig.debug
===================================================================
--- linux-2.6.16.orig/lib/Kconfig.debug
+++ linux-2.6.16/lib/Kconfig.debug
@@ -223,3 +223,10 @@ config RCU_TORTURE_TEST
at boot time (you probably don't).
Say M if you want the RCU torture tests to build as a module.
Say N if you are unsure.
+config PROFILE_LIKELY
+ bool "Record return values from likely/unlikely macros"
+ default n
+ help
+ Adds profiling on likely/unlikly macros . To see the
+ results of the profiling you can view the following,
+ /proc/likely_prof
Index: linux-2.6.16/lib/Makefile
===================================================================
--- linux-2.6.16.orig/lib/Makefile
+++ linux-2.6.16/lib/Makefile
@@ -49,6 +49,8 @@ obj-$(CONFIG_TEXTSEARCH_FSM) += ts_fsm.o

obj-$(CONFIG_SWIOTLB) += swiotlb.o

+obj-$(CONFIG_PROFILE_LIKELY) += likely_prof.o
+
hostprogs-y := gen_crc32table
clean-files := crc32table.h

Index: linux-2.6.16/lib/likely_prof.c
===================================================================
--- /dev/null
+++ linux-2.6.16/lib/likely_prof.c
@@ -0,0 +1,134 @@
+/*
+ * This code should enable profiling the likely and unlikely macros.
+ *
+ * Output goes in /prof/likely_prof
+ *
+ * Authors:
+ * Daniel Walker <dwalker@mvista.com>
+ * Hua Zhong <hzhong@gmail.com>
+ * Andrew Morton <akpm@osdl.org>
+ */
+
+#include <linux/init.h>
+#include <linux/types.h>
+#include <linux/fs.h>
+#include <linux/seq_file.h>
+#include <linux/proc_fs.h>
+#include <asm/bug.h>
+#include <asm/atomic.h>
+
+#define WAS_UNLIKELY 0
+#define WAS_LIKELY 1
+
+static struct likeliness *likeliness_head = NULL;
+
+static atomic_t likely_lock = ATOMIC_INIT(1);
+
+int do_check_likely(struct likeliness *likeliness, int ret)
+{
+ if (ret)
+ likeliness->count[1]++;
+ else
+ likeliness->count[0]++;
+
+ if (likeliness->type & LIKELY_UNSEEN) {
+ if (atomic_dec_and_test(&likely_lock)) {
+ if (likeliness->type & LIKELY_UNSEEN) {
+ likeliness->type &= (~LIKELY_UNSEEN);
+ likeliness->next = likeliness_head;
+ likeliness_head = likeliness;
+ }
+ }
+ atomic_inc(&likely_lock);
+ }
+
+ return ret;
+}
+
+static void * lp_seq_start(struct seq_file *out, loff_t *pos)
+{
+
+ if (!*pos) {
+
+ seq_printf(out, "Likely Profiling Results\n");
+ seq_printf(out, " --------------------------------------------------------------------\n");
+ seq_printf(out, "[+- ] Type | # True | # False | Function:Filename@Line\n");
+
+ out->private = (void *)likeliness_head;
+ }
+
+ return out->private;
+}
+
+static void * lp_seq_next(struct seq_file *out, void *p, loff_t *pos)
+{
+ struct likeliness * entry = (struct likeliness *) p;
+
+ if (entry->next) {
+ ++(*pos);
+ out->private = (void *)entry->next;
+ } else
+ out->private = NULL;
+
+ return (out->private);
+}
+
+static int lp_seq_show(struct seq_file *out, void *p)
+{
+ struct likeliness * entry = (struct likeliness *)p;
+ int true = entry->count[1], false = entry->count[0];
+
+ if (entry->type == WAS_UNLIKELY) {
+ if (true > false)
+ seq_printf(out, "+");
+ else
+ seq_printf(out, " ");
+
+ seq_printf(out, "unlikely ");
+ }
+ else if (entry->type == WAS_LIKELY) {
+ if (true < false)
+ seq_printf(out, "-");
+ else
+ seq_printf(out, " ");
+
+ seq_printf(out, "likely ");
+ }
+
+ seq_printf(out, "|%9u|%9u\t%s()@:%s@%d\n", true, false,
+ entry->func, entry->file, entry->line);
+
+ return 0;
+}
+
+static void lp_seq_stop(struct seq_file *m, void *p) { }
+
+struct seq_operations likely_profiling_ops = {
+ .start = lp_seq_start,
+ .next = lp_seq_next,
+ .stop = lp_seq_stop,
+ .show = lp_seq_show
+};
+
+static int lp_results_open(struct inode *inode, struct file *file)
+{
+ return seq_open(file, &likely_profiling_ops);
+}
+
+static struct file_operations proc_likely_operations = {
+ .open = lp_results_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = seq_release,
+};
+
+static int __init init_likely(void)
+{
+ struct proc_dir_entry *entry;
+ entry = create_proc_entry("likely_prof", 0, &proc_root);
+ if (entry)
+ entry->proc_fops = &proc_likely_operations;
+
+ return 0;
+}
+__initcall(init_likely);
-
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