一 用途
（1）function 主要用于跟踪内核函数的调用栈（其被调用过程）
（2）function_graph 主要用于跟踪内核函数内部调用流程及耗时
这两个对内核性能分析的作用不大，主要用来梳理内核模块的逻辑
二 使用
（1）function 使用
/sys/kernel/debug/tracing # echo nop > current_tracer ----清空跟踪器
/sys/kernel/debug/tracing # echo drm_open > set_ftrace_filter ----设置跟踪函数为drm_open
/sys/kernel/debug/tracing # echo function > current_tracer ----设置当前跟踪器
/sys/kernel/debug/tracing # echo 1 > options/func_stack_trace ----跟踪函数调用栈
/sys/kernel/debug/tracing # echo 1 > tracing_on ----开始跟踪
/sys/kernel/debug/tracing # /mnt/vkms_test ---运行vkms_test程序，其会调用到内核drm_open函数
/sys/kernel/debug/tracing # echo 0 > tracing_on ----关闭跟踪
/sys/kernel/debug/tracing # cat trace ----查看跟踪结果
# tracer: function
#
# entries-in-buffer/entries-written: 2/2 #P:4
#
# _-----=> irqs-off
# / _----=> need-resched
# | / _---=> hardirq/softirq
# || / _--=> preempt-depth
# ||| / delay
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
# | | | |||| | |
vkms_test-90 [001] .... 5408.290697: drm_open <-drm_stub_open
vkms_test-90 [001] .... 5408.291126: <stack trace>
=> drm_stub_open
=> chrdev_open
=> do_dentry_open
=> vfs_open
=> path_openat
=> do_filp_open
=> do_sys_openat2
=> do_sys_open
=> sys_open
=> ret_fast_syscall
=> 0xbebc3cdc
/sys/kernel/debug/tracing #
shell脚本：
/mnt # cat trace_fun.sh
# !/bin/sh
if [ $# -lt 2 ]; then
echo "usage:"
echo " sh trace_func.sh function exec_file"
exit -1
fi
cd /sys/kernel/debug/tracing/
echo nop > current_tracer
echo $1 > set_ftrace_filter
echo function > current_tracer
echo 1 > options/func_stack_trace
echo 1 > tracing_on
$2
echo 0 > tracing_on
cat trace
cd -
（2）function_graph使用
/sys/kernel/debug/tracing # echo nop > current_tracer
/sys/kernel/debug/tracing # echo function_graph > current_tracer
/sys/kernel/debug/tracing # echo drm_open > set_graph_function
/sys/kernel/debug/tracing # echo 1 > options/funcgraph-tail ----增加函数尾部注释
/sys/kernel/debug/tracing # echo > set_ftrace_filter ----清空，否则无法显示调用栈
/sys/kernel/debug/tracing # echo 1 > tracing_on
/sys/kernel/debug/tracing # /mnt/vkms_test
/sys/kernel/debug/tracing # echo 0 > tracing_on
/sys/kernel/debug/tracing # cat trace
# tracer: function_graph
#
# CPU DURATION FUNCTION CALLS
# | | | | | | |
2) | drm_open() {
2) | drm_minor_acquire() {
2) 8.625 us | _raw_spin_lock_irqsave();
2) 4.709 us | _raw_spin_unlock_irqrestore();
2) | drm_dev_enter() {
2) 5.750 us | __srcu_read_lock();
2) + 17.167 us | } /* drm_dev_enter */
2) 5.791 us | __srcu_read_unlock();
2) + 75.458 us | } /* drm_minor_acquire */
2) 6.833 us | __drm_dbg();
2) | drm_file_alloc() {
2) | kmem_cache_alloc_trace() {
2) 5.583 us | should_failslab();
2) | __slab_alloc.constprop.19() {
2) | ___slab_alloc.constprop.20() {
2) 3.583 us | _raw_spin_lock();
2) | alloc_debug_processing() {
2) | check_slab() {
2) 4.750 us | slab_pad_check.part.8();
2) + 12.375 us | } /* check_slab */
2) | check_object() {
2) 4.250 us | check_bytes_and_report();
2) 4.166 us | check_bytes_and_report();
2) 3.709 us | check_bytes_and_report();
2) 3.250 us | check_bytes_and_report();
2) 3.417 us | check_bytes_and_report();
2) + 39.792 us | } /* check_object */
2) | set_track() {
2) | stack_trace_save() {
2) | save_stack_trace() {
2) | __save_stack_trace() {
2) 3.042 us | save_trace();
2) 2.958 us | save_trace();
2) 2.959 us | save_trace();
2) 2.959 us | save_trace();
2) 2.958 us | save_trace();
2) 3.000 us | save_trace();
2) 3.166 us | save_trace();
2) 3.042 us | save_trace();
2) 3.000 us | save_trace();
2) 3.000 us | save_trace();
2) 3.042 us | save_trace();
2) 3.041 us | save_trace();
2) 3.041 us | save_trace();
2) 3.000 us | save_trace();
2) 3.125 us | save_trace();
2) 3.000 us | save_trace();
2) 3.042 us | save_trace();
2) 3.042 us | save_trace();
2) 3.042 us | save_trace();
2) 3.083 us | save_trace();
2) ! 125.875 us | } /* __save_stack_trace */
2) ! 132.041 us | } /* save_stack_trace */
2) ! 138.375 us | } /* stack_trace_save */
2) ! 145.208 us | } /* set_track */
2) 4.375 us | init_object();
2) ! 218.625 us | } /* alloc_debug_processing */
2) | deactivate_slab() {
2) 4.042 us | _raw_spin_lock();
2) + 16.833 us | } /* deactivate_slab */
2) ! 257.708 us | } /* ___slab_alloc.constprop.20 */
2) ! 272.709 us | } /* __slab_alloc.constprop.19 */
2) ! 319.792 us | } /* kmem_cache_alloc_trace */
2) | capable() {
2) | ns_capable_common() {
2) 6.500 us | cap_capable();
2) + 20.375 us | } /* ns_capable_common */
2) + 40.959 us | } /* capable */
2) 5.958 us | __mutex_init();
2) 6.792 us | __init_waitqueue_head();
2) 5.791 us | __mutex_init();
2) 7.084 us | drm_gem_open();
2) | drm_prime_init_file_private() {
2) 6.958 us | __mutex_init();
2) + 32.208 us | } /* drm_prime_init_file_private */
2) ! 492.709 us | } /* drm_file_alloc */
2) | drm_master_open() {
2) 7.667 us | mutex_lock();
2) | drm_new_set_master() {
2) | drm_master_create() {
2) | kmem_cache_alloc_trace() {
2) 5.709 us | should_failslab();
2) | __slab_alloc.constprop.19() {
2) | ___slab_alloc.constprop.20() {
2) 3.792 us | _raw_spin_lock();
2) | alloc_debug_processing() {
2) | check_slab() {
2) 3.417 us | slab_pad_check.part.8();
2) + 10.291 us | } /* check_slab */
2) | check_object() {
2) 3.834 us | check_bytes_and_report();
2) 3.208 us | check_bytes_and_report();
2) 3.958 us | check_bytes_and_report();
2) 3.375 us | check_bytes_and_report();
2) 3.375 us | check_bytes_and_report();
2) + 53.583 us | } /* check_object */
2) | set_track() {
2) | stack_trace_save() {
2) | save_stack_trace() {
2) | __save_stack_trace() {
2) 3.416 us | save_trace();
2) 3.042 us | save_trace();
2) 3.000 us | save_trace();
2) 3.000 us | save_trace();
2) 2.958 us | save_trace();
2) 2.959 us | save_trace();
2) 3.042 us | save_trace();
2) 3.000 us | save_trace();
2) 3.125 us | save_trace();
2) 3.042 us | save_trace();
2) 3.000 us | save_trace();
2) 3.292 us | save_trace();
2) 3.083 us | save_trace();
2) 3.042 us | save_trace();
2) 2.959 us | save_trace();
2) 3.000 us | save_trace();
2) 3.000 us | save_trace();
2) 3.000 us | save_trace();
2) 3.000 us | save_trace();
2) 3.000 us | save_trace();
2) 3.000 us | save_trace();
2) 3.083 us | save_trace();
2) ! 137.583 us | } /* __save_stack_trace */
2) ! 143.833 us | } /* save_stack_trace */
2) ! 149.875 us | } /* stack_trace_save */
2) ! 156.166 us | } /* set_track */
2) 3.833 us | init_object();
2) ! 240.416 us | } /* alloc_debug_processing */
2) | deactivate_slab() {
2) 3.458 us | _raw_spin_lock();
2) + 12.000 us | } /* deactivate_slab */
2) ! 273.333 us | } /* ___slab_alloc.constprop.20 */
2) ! 285.708 us | } /* __slab_alloc.constprop.19 */
2) ! 310.667 us | } /* kmem_cache_alloc_trace */
2) ! 324.167 us | } /* drm_master_create */
2) + 10.917 us | drm_set_master();
2) ! 382.250 us | } /* drm_new_set_master */
2) 6.333 us | mutex_unlock();
2) ! 429.625 us | } /* drm_master_open */
2) 6.500 us | mutex_lock();
2) 5.708 us | mutex_unlock();
2) # 1116.667 us | } /* drm_open */
/sys/kernel/debug/tracing #
shell脚本：
/mnt # cat trace_fun_graph.sh
# !/bin/sh
if [ $# -lt 2 ]; then
echo "usage:"
echo " sh trace_func_graph.sh function exec_file"
exit -1
fi
cd /sys/kernel/debug/tracing/
echo nop > current_tracer
echo function_graph > current_tracer
echo $1 > set_graph_function
echo 1 > options/funcgraph-tail
echo > set_ftrace_filter
echo 1 > tracing_on
$2
echo 0 > tracing_on
cat trace
cd -