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Subject[PATCH][RFC] ftrace: function oprofiler
[
It was late at night, I didn't feel like sleeping so I wrote up
this new utility for ftrace.

This is not ready for inclussion, but produces nice information.
It hooks into the ftrace function tracer to produce a count of
all the functions that are hit.

Paul, I used the RCU hlist manipulations to read and add fuctions
to a list. I never delete (except for clearing out the array, with
a memcpy). The comments say the that the iterator must be protected
by a rcu_read_lock. Is this true? Basically, I protect it by
preempt disable and a local counter that prevents the code from
being reentered by an interrupt.

]

This is a function profiler to count the number of times a function is hit.
It creates two files:

/debugfs/tracing/ftrace_profile_enable
/debugfs/tracing/ftrace_profile

For example, to run this I did this as soon as I was able to log in.

# echo 1 > /debug/tracing/ftrace_profile_enable
[ waited a while for the rest of the boot process to run. ]

# echo 0 > /debug/tracing/ftrace_profile_enable
And then I was able to get a list of counts functions were hit.

# cat /debug/tracing/ftrace_profile | head
entries: 2274
overruns: 0
COUNT FUNCTION
7628 : dnotify_parent+0xd/0x78
10101 : hrtimer_get_next_event+0x11/0xc7
17937 : inotify_dentry_parent_queue_event+0x11/0x94
17952 : inotify_inode_queue_event+0x11/0xe1
10103 : rcu_needs_cpu+0x4/0x53
1 : printk_needs_cpu+0x4/0x27
7314 : printk_needs_cpu+0x4/0x27

I preallocate 5000 entries (later this needs to be configurable).
If we hit more than 5000 functions, they are counted in the overruns.
The above output shows that we had 2274 functions that we recorded.
All will list if I did not do the "head".

I'm also able to use sort to get the top 20 hits:

# cat /debug/tracing/ftrace_profile | sort -brn | head -20
280075 : __rcu_read_unlock+0xb/0xa2
280065 : __rcu_read_lock+0x11/0xb3
262811 : dput+0x7/0x162
138868 : path_put+0x9/0x35
117843 : __phys_addr+0x4/0x39
116320 : current_kernel_time+0x8/0x34
111272 : kfree+0x11/0xda
101832 : unroll_tree_refs+0x11/0xb4
101769 : audit_syscall_exit+0x11/0x312
101702 : audit_syscall_entry+0x11/0x181
90910 : set_normalized_timespec+0x4/0x38
88359 : getnstimeofday+0x7/0x9e
88309 : ktime_get_ts+0x7/0x53
85135 : kmem_cache_free+0x11/0xb9
83917 : ktime_get+0x8/0x47
51756 : fget+0x7/0x83
48623 : mntput_no_expire+0x11/0x140
46224 : vm_normal_page+0x4/0x2c
41200 : put_page+0xd/0xf5
39938 : sys_fcntl+0x11/0x344

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
---
kernel/trace/Kconfig | 11 +
kernel/trace/Makefile | 1
kernel/trace/trace_oprofile.c | 341 ++++++++++++++++++++++++++++++++++++++++++
3 files changed, 353 insertions(+)
Index: linux-tip.git/kernel/trace/trace_oprofile.c
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-tip.git/kernel/trace/trace_oprofile.c 2008-10-25 01:33:29.000000000 -0400
@@ -0,0 +1,341 @@
+/*
+ * Function profiler
+ *
+ * Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
+ */
+#include <linux/kallsyms.h>
+#include <linux/seq_file.h>
+#include <linux/spinlock.h>
+#include <linux/debugfs.h>
+#include <linux/uaccess.h>
+#include <linux/module.h>
+#include <linux/ftrace.h>
+#include <linux/hash.h>
+#include <linux/fs.h>
+#include <asm/local.h>
+#include "trace.h"
+
+#define FTRACE_PROFILE_HASHBITS 10
+#define FTRACE_PROFILE_HASHSIZE (1<<FTRACE_PROFILE_HASHBITS)
+
+static DEFINE_PER_CPU(local_t, trace_active);
+static int ftrace_profile_enabled;
+
+struct ftrace_node {
+ struct hlist_node node;
+ unsigned long ip;
+ unsigned long count;
+};
+
+static struct hlist_head function_hash[FTRACE_PROFILE_HASHSIZE];
+
+/* TODO: make user configurable */
+static int ftrace_hash_size = 5000;
+static int ftrace_hash_occupied;
+static int ftrace_hash_overrun;
+
+static struct ftrace_node *ftrace_node_list;
+static struct ftrace_node *ftrace_free_node;
+
+static raw_spinlock_t ftrace_profile_lock =
+ (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
+
+static int
+ftrace_profile_alloc_hash_list(void)
+{
+ /* FIXME: size may be too much for kmalloc */
+ ftrace_node_list = kzalloc(sizeof(struct ftrace_node) *
+ ftrace_hash_size, GFP_KERNEL);
+ if (!ftrace_node_list)
+ return -ENOMEM;
+
+ ftrace_free_node = ftrace_node_list;
+
+ return 0;
+}
+
+static void
+ftrace_profile_init_hash(void)
+{
+ ftrace_free_node = ftrace_node_list;
+ memset(ftrace_node_list, 0, sizeof(*ftrace_node_list) *
+ ftrace_hash_size);
+}
+
+static void
+ftrace_profile_free_hash_list(void)
+{
+ kfree(ftrace_node_list);
+
+ ftrace_node_list = ftrace_free_node = NULL;
+}
+
+static struct ftrace_node *
+ftrace_profile_alloc_node(void)
+{
+ if (ftrace_hash_occupied >= ftrace_hash_size)
+ return NULL;
+
+ ftrace_hash_occupied++;
+
+ return ftrace_free_node++;
+}
+
+static struct ftrace_node *
+ftrace_ip_in_hash(unsigned long ip, unsigned long key)
+{
+ struct ftrace_node *p;
+ struct hlist_node *t;
+
+ hlist_for_each_entry_rcu(p, t, &function_hash[key], node) {
+ if (p->ip == ip)
+ return p;
+ }
+
+ return NULL;
+}
+
+static inline void
+ftrace_add_hash(struct ftrace_node *node, unsigned long key)
+{
+ unsigned long flags;
+
+ local_irq_save(flags);
+ __raw_spin_lock(&ftrace_profile_lock);
+ hlist_add_head_rcu(&node->node, &function_hash[key]);
+ __raw_spin_unlock(&ftrace_profile_lock);
+ local_irq_restore(flags);
+}
+
+static void
+ftrace_profile_trace_call(unsigned long ip, unsigned long parent_ip)
+{
+ struct ftrace_node *p;
+ int cpu, resched;
+ unsigned long key;
+
+ if (unlikely(!ftrace_enabled || !ftrace_profile_enabled))
+ return;
+
+ resched = need_resched();
+ preempt_disable_notrace();
+
+ cpu = raw_smp_processor_id();
+ if (local_inc_return(&per_cpu(trace_active, cpu)) != 1)
+ goto out;
+
+ key = hash_long(ip, FTRACE_PROFILE_HASHBITS);
+ p = ftrace_ip_in_hash(ip, key);
+
+ if (!p) {
+ p = ftrace_profile_alloc_node();
+ if (!p) {
+ ftrace_hash_overrun++;
+ goto out;
+ }
+ p->ip = ip;
+ ftrace_add_hash(p, key);
+ }
+
+ p->count++;
+
+
+ out:
+ local_dec(&per_cpu(trace_active, cpu));
+ /* prevent recursion in schedule */
+ if (resched)
+ preempt_enable_no_resched_notrace();
+ else
+ preempt_enable_notrace();
+}
+
+static struct ftrace_ops trace_ops __read_mostly =
+{
+ .func = ftrace_profile_trace_call,
+};
+
+static void *
+t_next(struct seq_file *m, void *v, loff_t *pos)
+{
+ long i = (long)m->private;
+
+ (*pos)++;
+
+ i++;
+
+ if (i >= ftrace_hash_occupied)
+ return NULL;
+
+ m->private = (void *)i;
+
+ return &m->private;
+}
+
+static void *t_start(struct seq_file *m, loff_t *pos)
+{
+ void *t = &m->private;
+ loff_t l = 0;
+
+ local_irq_disable();
+
+ for (; t && l < *pos; t = t_next(m, t, &l))
+ ;
+
+ return t;
+}
+
+static void t_stop(struct seq_file *m, void *p)
+{
+ local_irq_enable();
+}
+
+static int trace_lookup_hash(struct seq_file *m, long i)
+{
+ unsigned long addr = ftrace_node_list[i].ip;
+#ifdef CONFIG_KALLSYMS
+ char str[KSYM_SYMBOL_LEN];
+
+ sprint_symbol(str, addr);
+
+ return seq_printf(m, "%s\n", str);
+#else
+ return seq_printf(m, "%p\n", (void*)addr);
+#endif
+}
+
+static int t_show(struct seq_file *m, void *v)
+{
+ long i = *(long *)v;
+
+ if (i < 0) {
+ seq_printf(m, "entries: %d\n", ftrace_hash_occupied);
+ seq_printf(m, "overruns: %d\n", ftrace_hash_overrun);
+
+ seq_printf(m, " COUNT FUNCTION\n");
+ return 0;
+ }
+
+ if (i >= ftrace_hash_occupied)
+ return 0;
+
+ seq_printf(m, " %8lu : ", ftrace_node_list[i].count);
+ trace_lookup_hash(m, i);
+
+ return 0;
+}
+
+static struct seq_operations ftrace_profile_seq_ops = {
+ .start = t_start,
+ .next = t_next,
+ .stop = t_stop,
+ .show = t_show,
+};
+
+static int ftrace_profile_open(struct inode *inode, struct file *file)
+{
+ int ret;
+
+ ret = seq_open(file, &ftrace_profile_seq_ops);
+ if (!ret) {
+ struct seq_file *m = file->private_data;
+ m->private = (void *)-1;
+ }
+
+ return ret;
+}
+
+static struct file_operations ftrace_profile_fops = {
+ .open = ftrace_profile_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+};
+
+static ssize_t
+ftrace_profile_enable_read(struct file *filp, char __user *ubuf,
+ size_t cnt, loff_t *ppos)
+{
+ char buf[64];
+ int r;
+
+ r = sprintf(buf, "%d\n", ftrace_profile_enabled);
+ return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
+}
+
+static ssize_t
+ftrace_profile_enable_write(struct file *filp, const char __user *ubuf,
+ size_t cnt, loff_t *ppos)
+{
+ char buf[64];
+ long val;
+ int ret;
+
+ if (!ftrace_node_list)
+ return -ENODEV;
+
+ if (cnt >= sizeof(buf))
+ return -EINVAL;
+
+ if (copy_from_user(&buf, ubuf, cnt))
+ return -EFAULT;
+
+ buf[cnt] = 0;
+
+ ret = strict_strtoul(buf, 10, &val);
+ if (ret < 0)
+ return ret;
+
+ val = !!val;
+
+ if (val == ftrace_profile_enabled)
+ goto out;
+
+ if (val) {
+ /* start it up */
+ ftrace_profile_init_hash();
+ register_ftrace_function(&trace_ops);
+ ftrace_profile_enabled = 1;
+ } else {
+ ftrace_profile_enabled = 0;
+ unregister_ftrace_function(&trace_ops);
+ }
+
+ out:
+ filp->f_pos += cnt;
+
+ return cnt;
+}
+
+static struct file_operations ftrace_profile_enable_fops = {
+ .open = tracing_open_generic,
+ .read = ftrace_profile_enable_read,
+ .write = ftrace_profile_enable_write,
+};
+
+
+static __init int ftrace_profile_init(void)
+{
+ struct dentry *d_tracer;
+ struct dentry *entry;
+ int ret;
+
+ ret = ftrace_profile_alloc_hash_list();
+ if (ret)
+ return ret;
+
+ d_tracer = tracing_init_dentry();
+
+ entry = debugfs_create_file("ftrace_profile_enable", 0644, d_tracer,
+ NULL, &ftrace_profile_enable_fops);
+ if (!entry)
+ pr_warning("Could not create debugfs 'ftrace_profile_enable' entry\n");
+
+ entry = debugfs_create_file("ftrace_profile", 0444, d_tracer,
+ NULL, &ftrace_profile_fops);
+ if (!entry)
+ pr_warning("Could not create debugfs 'ftrace_profile' entry\n");
+
+
+ return 0;
+}
+
+device_initcall(ftrace_profile_init);
Index: linux-tip.git/kernel/trace/Kconfig
===================================================================
--- linux-tip.git.orig/kernel/trace/Kconfig 2008-10-23 12:55:37.000000000 -0400
+++ linux-tip.git/kernel/trace/Kconfig 2008-10-25 00:57:40.000000000 -0400
@@ -156,6 +156,17 @@ config STACK_TRACER

Say N if unsure.

+config FUNCTION_PROFILER
+ bool "Trace max stack"
+ depends on HAVE_FUNCTION_TRACER
+ depends on DEBUG_KERNEL
+ select FUNCTION_TRACER
+ help
+ This special tracer that makes a histogram of all the functions
+ that it encounters.
+
+ Say N if unsure.
+
config DYNAMIC_FTRACE
bool "enable/disable ftrace tracepoints dynamically"
depends on FUNCTION_TRACER
Index: linux-tip.git/kernel/trace/Makefile
===================================================================
--- linux-tip.git.orig/kernel/trace/Makefile 2008-10-23 12:55:37.000000000 -0400
+++ linux-tip.git/kernel/trace/Makefile 2008-10-25 00:58:07.000000000 -0400
@@ -22,6 +22,7 @@ obj-$(CONFIG_PREEMPT_TRACER) += trace_ir
obj-$(CONFIG_SCHED_TRACER) += trace_sched_wakeup.o
obj-$(CONFIG_NOP_TRACER) += trace_nop.o
obj-$(CONFIG_STACK_TRACER) += trace_stack.o
+obj-$(CONFIG_FUNCTION_PROFILER) += trace_oprofile.o
obj-$(CONFIG_MMIOTRACE) += trace_mmiotrace.o
obj-$(CONFIG_BOOT_TRACER) += trace_boot.o



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