Song Baohua: A complete case of ftrace

Ftrace Introduction

Ftrace is one of the most effective tools for Linux to do code-level practice analysis, such as we make a system call, out of time, we want to know where the time spent, using ftrace can be traced to the first level of time distribution. Ftrace Case

Write a proc module that contains a proc read and write entry. Test_proc_show () intentionally invokes a kill_time () function, while the Kill_time () function calls the Mdelay (2) and kill_moretime () functions, which call Mdelay (2).

The Kill_time () function and the Kill_moretime () function are preceded by noinline to avoid being optimized by the compiler inline.

#include <linux/module.h> #include <linux/kernel.h> #include <linux/init.h> #include <linux/ version.h> #include <linux/proc_fs.h> #include <linux/seq_file.h> #include <linux/delay.h> #
Include <linux/uaccess.h> static unsigned int variable;

static struct Proc_dir_entry *test_dir, *test_entry; 
static noinline void Kill_moretime (void) {Mdelay (2);} static noinline void Kill_time (void) {Mdelay (2); Kill_moretime (); static int test_proc_show (struct seq_file *seq, void *v) {unsigned int *ptr_var = seq->private; kill_time (); seq_p
rintf (seq, "%u\n", *ptr_var);
return 0;

Static ssize_t test_proc_write (struct file *file, const char __user *buffer, size_t count, loff_t *ppos) {...} static int Test_proc_open (struct inode *inode, struct file *file) {return Single_open (file, Test_proc_show, Pde_data (Inod
e)); static const struct File_operations test_proc_fops = {. Owner = This_module,. Open = Test_proc_open,. Read = Seq_read,. Write = Test_proc_write,. Llseek = Seq_lseek,. Release = Single_release,}; static __init int Test_proc_init (void) {Test_dir = Proc_mkdir ("Test_dir", NULL); if (test_dir) {test_entry = Proc_create
_data ("TEST_RW", 0666, Test_dir, &test_proc_fops, &variable);
if (Test_entry) return 0;
} Return-enomem;
} module_init (Test_proc_init); static __exit void Test_proc_cleanup (void) {Remove_proc_entry ("TEST_RW", Test_dir); Remove_proc_entry ("Test_dir",
NULL);


} module_exit (Test_proc_cleanup);
Module_author ("Barry Song <baohua@kernel.org>");
Module_description ("proc exmaple"); Module_license ("GPL v2");

The module corresponds to the makefile as follows:

Kvers = $ (Shell uname-r)

# Kernel Modules

obj-m + = PROC.O

# Specify flags for the module compilation.

#EXTRA_CFLAGS =-g-o0

build:kernel_modules
kernel_modules:
 make-c/lib/modules/$ (kvers)/build m=$ ( CurDir) Modules Clean
:
 make-c/lib/modules/$ (kvers)/build m=$ (CurDir) Clean

Compile and load:

$ make

baohua@baohua-perf:~/develop/training/debug/ftrace/proc$

$ sudo insmod Proc.ko

[sudo] password for Baohua:

The/PROC/TEST_DIR/TEST_RW file can be read/write after the/proc directory.

Below we use Ftrace to track the function of Test_proc_show ().

We wrote all the commands that started ftrace into a script function.sh:

#!/bin/bash
debugfs=/sys/kernel/debug
echo nop > $debugfs/tracing/current_tracer
echo 0 > $debugfs /tracing/tracing_on
echo $$ > $debugfs/tracing/set_ftrace_pid
echo function_graph > $debugfs/tracing/ Current_tracer
#replace test_proc_show by your function name
echo test_proc_show > $debugfs/tracing/set_ Graph_function
echo 1 > $debugfs/tracing/tracing_on
exec "$@"

Then use this script to start the CAT/PROC/TEST_DIR/TEST_RW so that the Test_proc_show () function under Ftrace is trace.

#./function.sh CAT/PROC/TEST_DIR/TEST_RW

0

Read the result of trace:

# Cat/sys/kernel/debug/tracing/trace > 1

Then using VIM to open this file 1, found that this file has more than 600 lines:

Days, long to see not clear.

Ftrace How to read the results.

Ftrace How to read the results. The answer is very simple: if it is a leaf function, directly in front of this function to show the time it takes, if it is not the leaves, to wait until}, then show time, the following figure:

The larger part of the delay, there will be +, #等特殊标号:

' $ '-greater than 1 second
' @ '-greater than milisecond
' * '-greater than milisecond
' # '-Greater than 1000 microsecond
'! '-greater than microsecond
' + '-greater than microsecond
'-less than or equal to microsecond.

vim folds the Ftrace

The Ftrace file above is too big to see clearly. We can use Vim to fold, but need a special configuration of vim, I put it in my ~ directory, named. Fungraph-vim:

"Enable folding for Ftrace function_graph traces.

"

' To-use,: source this file while viewing a function_graph trace, or use vim ' s

' s option to load ' command-line together with a trace. You can then

"Use the usual vim fold commands, such as" Za ", to open and close nested

"Functions. While closed, a fold'll show the total time taken for a call,

"As would normally appear on the line with the closing brace. Folded

"Functions would not include finish_task_switch (), so folding should remain

"Relatively sane even through a context switch.

"

"Note, this would almost certainly only work OK with a

"Single-cpu Trace (e.g. trace-cmd,--CPU 1).

function! FUNCTIONGRAPHFOLDEXPR (Lnum)

Let-line = Getline (a:lnum)

If line[-1:] = = ' {'

If line =~ ' Finish_task_switch () {$ '

Return ' >1 '

endif

Return ' A1 '

ElseIf line[-1:] = = '} '

Return ' s1 '

Else

return ' = '

endif

Endfunction

function! Functiongraphfoldtext ()

Let S = Split (Getline (V:foldstart), ' | ', 1)

If Getline (v:foldend+1) =~ ' Finish_task_switch () {$ '

Let s[2] = ' Task switch '

Else

Let E = Split (Getline (v:foldend), ' | ', 1)

Let s[2] = e[2]

endif

Return join (S, ' | ')

Endfunction

Setlocal foldexpr=functiongraphfoldexpr (V:lnum)

Setlocal Foldtext=functiongraphfoldtext ()

Setlocal foldcolumn=12

Setlocal foldmethod=expr

After that, we configure VIM to open the previous 600-line file 1 for this template:

Vim-s ~/.fungraph-vim 1

So the way we see it is:

We can move the cursor to line 5th, the keyboard beats za, then expand to:

Continue to expand the 6th line of Kill_time (), press za:

We can use Z, a two buttons to search for or expand ftrace results.

Finally, the Ftrace function of the https://github.com/brendangregg/perf-tools is well encapsulated and integrated, it is recommended to use the Perf-tools to Ftrace, the effect is better and simpler.

Talk about Perf-tools again when you are free.