Ftrace相關(guān)的文章

1、Ftrace 是什么東西？

Ftrace是一個(gè)直接內(nèi)置在Linux內(nèi)核中的跟蹤工具。許多發(fā)行版在最近的發(fā)行版中已經(jīng)啟用了各種各樣的Ftrace配置。Ftrace給Linux帶來的好處之一是能夠看到內(nèi)核中發(fā)生了什么。因此，這使得發(fā)現(xiàn)問題區(qū)域或簡單地跟蹤奇怪的bug變得更容易管理。

上面那段話是直接翻譯過來的，原文如下，我比較推薦大家直接看英文

Ftrace is a tracing utility built directly into the Linux kernel. Many distributions already have various configurations of Ftrace enabled in their most recent releases. One of the benefits that Ftrace brings to Linux is the ability to see what is happening inside the kernel. As such, this makes finding problem areas or simply tracking down that strange bug more manageable.

2、怎么使用Ftrace

我的實(shí)驗(yàn)平臺是MT8167、Linux4.4內(nèi)核

2.1、配置內(nèi)核宏

weiqifa@bsp-ubuntu1804:~/is10-sdk$?git?diff?kernel-4.4/
diff?--git?a/kernel-4.4/arch/arm/configs/xxx_defconfig?
b/kernel-4.4/arch/arm/configs/xxx_defconfig
index?8da5210003..a88e53253f?100755
---?a/kernel-4.4/arch/arm/configs/xxx_defconfig
+++?b/kernel-4.4/arch/arm/configs/xxx_defconfig
@@?-400,3?+400,7?@@?CONFIG_USB_RTL8152=y
?CONFIG_USB_NET_DRIVERS=y
?CONFIG_GPIO_CONTROL=y
?#CONFIG_POGO_PIN=y
+CONFIG_FUNCTION_TRACER=y
+CONFIG_FUNCTION_GRAPH_TRACER=y
+CONFIG_STACK_TRACER=y
+CONFIG_DYNAMIC_FTRACE=y

2.2、燒錄boot.img 重新開機(jī)

2.3、查看是否生效

進(jìn)入ftrace 目錄

xxx:/?#?cd?/sys/kernel/debug/tracing
xxx:/sys/kernel/debug/tracing?#?ls
README?????????????????????enabled_functions?saved_cmdlines??????set_graph_function?trace_marker
available_events???????????events????????????saved_cmdlines_size?set_graph_notrace??trace_options
available_filter_functions?free_buffer???????saved_tgids?????????snapshot???????????trace_pipe
available_tracers??????????instances?????????set_event???????????stack_max_size?????tracing_cpumask
buffer_size_kb?????????????max_graph_depth???set_event_pid???????stack_trace????????tracing_max_latency
buffer_total_size_kb???????options???????????set_ftrace_filter???stack_trace_filter?tracing_on
current_tracer?????????????per_cpu???????????set_ftrace_notrace??trace??????????????tracing_thresh
dyn_ftrace_total_info??????printk_formats????set_ftrace_pid??????trace_clock
xxx:/sys/kernel/debug/tracing?#

查看內(nèi)核支持的跟蹤器列表

xxx:/sys/kernel/debug/tracing?#?cat?available_tracers
function_graph?function?nop
xxx:/sys/kernel/debug/tracing?#

Tracer有很多種，主要幾大類：

函數(shù)類：function， function_graph， stack
延時(shí)類：irqsoff， preemptoff， preemptirqsoff， wakeup， wakeup_rt， waktup_dl
其他類：nop， mmiotrace， blk

使能function_graph跟蹤器

echo?function_graph?>?current_tracer

查看當(dāng)前的跟蹤器

xxx:/sys/kernel/debug/tracing?#?cat?current_tracer
function_graph
xxx:/sys/kernel/debug/tracing?#

使能ftrace 功能

xxx:/sys/kernel/debug/tracing?#?echo?1?>?tracing_on

查看ftrace輸出

1|Knowin?inSight10:/sys/kernel/debug/tracing?#?cat?trace?|?head?-40
#?tracer:?function_graph
#
#?CPU??DURATION??????????????????FUNCTION?CALLS
#?|?????|???|?????????????????????|???|???|???|
?2)???4.000?us????|??????????}?/*?path_init?*/
?2)???????????????|??????????link_path_walk()?{
?2)???????????????|????????????inode_permission2()?{
?2)???????????????|??????????????__inode_permission2()?{
?2)???????????????|????????????????generic_permission()?{
?2)???0.384?us????|??????????????????in_group_p();
?2)???2.154?us????|????????????????}
?2)???????????????|????????????????security_inode_permission()?{
?2)???????????????|??????????????????selinux_inode_permission()?{
?2)???0.231?us????|????????????????????__rcu_read_lock();
?2)???0.308?us????|????????????????????avc_lookup();
?2)???0.231?us????|????????????????????__rcu_read_unlock();
?2)???5.923?us????|??????????????????}
?2)???7.846?us????|????????????????}
?2)?+?13.538?us???|??????????????}
?2)?+?15.308?us???|????????????}
?2)???????????????|????????????walk_component()?{
?2)???????????????|??????????????lookup_fast()?{
?2)???0.307?us????|????????????????__d_lookup_rcu();
?2)???0.307?us????|????????????????__lookup_mnt();
?2)???4.231?us????|??????????????}
?2)???6.077?us????|????????????}
?2)???????????????|????????????inode_permission2()?{
?2)???????????????|??????????????__inode_permission2()?{
?3)???3.923?us????|??????????????????????}?/*?down_trylock?*/
?2)???????????????|????????????????generic_permission()?{
?3)???6.538?us????|????????????????????}?/*?console_trylock?*/
?2)???0.308?us????|??????????????????in_group_p();
?3)???????????????|????????????????????console_unlock()?{
?3)???0.231?us????|??????????????????????_raw_spin_lock_irqsave();
?2)???2.231?us????|????????????????}
?2)???????????????|????????????????security_inode_permission()?{
?2)???????????????|??????????????????selinux_inode_permission()?{
?3)???0.308?us????|??????????????????????_raw_spin_unlock_irqrestore();
?2)???0.231?us????|????????????????????__rcu_read_lock();
?3)???0.231?us????|??????????????????????_raw_spin_lock_irqsave();
Knowin?inSight10:/sys/kernel/debug/tracing?#

3、Ftrace 其他使用特點(diǎn)

直接cat trace 文件，內(nèi)容太多了，我們可以通過設(shè)置filter來設(shè)置過濾函數(shù)。

為了方便使用，set_ftrace_filter 文件還支持簡單格式的通配符。

value* 選擇所有名字以 value字串開頭的函數(shù)
*value* 選擇所有名字中包含 value字串的函數(shù)
*value 選擇所有名字以 value字串結(jié)尾的函數(shù)

設(shè)置filter

xxx:/sys/kernel/debug/tracing?#?echo?raw*?>?set_ftrace_filter
xxx:/sys/kernel/debug/tracing?#

再查看trace文件

xxx:/sys/kernel/debug/tracing?#?cat?trace
#?tracer:?function_graph
#
#?CPU??DURATION??????????????????FUNCTION?CALLS
#?|?????|???|?????????????????????|???|???|???|
?2)???1.693?us????|??raw_local_deliver();
?2)???0.308?us????|??raw_local_deliver();
?2)???1.000?us????|??raw_notifier_call_chain();
?2)???2.077?us????|??raw_notifier_call_chain();
?2)???1.923?us????|??raw_local_deliver();
?------------------------------------------
?2)??ntloop--1393??=>????<...>-16
?------------------------------------------

?2)???0.308?us????|??raw_local_deliver();
?------------------------------------------
?2)????<...>-16????=>????-0
?------------------------------------------

?2)???0.307?us????|??raw_notifier_call_chain();
?2)???0.846?us????|??raw_notifier_call_chain();
?2)???0.385?us????|??raw_notifier_call_chain();
?------------------------------------------
?2)????-0????=>??droid.b-4348
?------------------------------------------

?2)???1.000?us????|??raw_notifier_call_chain();
?2)???1.384?us????|??raw_notifier_call_chain();
?------------------------------------------
?2)??droid.b-4348??=>??Binder:-524
?------------------------------------------

?2)???0.923?us????|??raw_notifier_call_chain();
?2)???1.077?us????|??raw_notifier_call_chain();
?------------------------------------------
?2)??Binder:-524???=>??droid.b-4348
?------------------------------------------

?2)???1.000?us????|??raw_notifier_call_chain();
?------------------------------------------
?2)??droid.b-4348??=>??Binder:-524
?------------------------------------------

?2)???1.231?us????|??raw_notifier_call_chain();
?------------------------------------------
?2)??Binder:-524???=>??droid.b-4348
?------------------------------------------

?2)???1.077?us????|??raw_notifier_call_chain();
?2)???1.692?us????|??raw_notifier_call_chain();
?2)???2.000?us????|??raw_notifier_call_chain();
?2)???1.000?us????|??raw_notifier_call_chain();
?2)???0.923?us????|??raw_notifier_call_chain();
?2)???0.462?us????|??raw_notifier_call_chain();
?2)???1.000?us????|??raw_notifier_call_chain();
?2)???0.846?us????|??raw_notifier_call_chain();

查看中間字符串

xxx:/sys/kernel/debug/tracing?#?echo?*touch*?>?set_ftrace_filter

查看trace

xxx:/sys/kernel/debug/tracing?#?cat?trace?|head?-40
#?tracer:?function_graph
#
#?CPU??DURATION??????????????????FUNCTION?CALLS
#?|?????|???|?????????????????????|???|???|???|
?0)???????????????|??/*?6?[cpu_loading]?not_reset_cpu_loading?*/
?0)???????????????|??/*?6?[cpu_loading]?update?cpu_loading?*/
?0)???????????????|??/*?6?[cpu_loading]?cur_idle_time[0].time:933317139?cur_wall_time[0].time:1008009932
?*/
?0)???????????????|??/*?6?[cpu_loading]?cur_idle_time[1].time:936071150?cur_wall_time[1].time:1008009942
?*/
?0)???????????????|??/*?6?[cpu_loading]?cur_idle_time[2].time:917091836?cur_wall_time[2].time:1008009946
?*/
?0)???????????????|??/*?6?[cpu_loading]?cur_idle_time[3].time:890438730?cur_wall_time[3].time:1008009950
?*/
?0)???????????????|??/*?6?[cpu_loading]?cur_idle_time[0].time:933317139?cur_wall_time[0].time:1008009932
?*/
?0)???????????????|??/*?6?[cpu_loading]?cur_idle_time[1].time:936071150?cur_wall_time[1].time:1008009942
?*/
?0)???????????????|??/*?6?[cpu_loading]?cur_idle_time[2].time:917091836?cur_wall_time[2].time:1008009946
?*/
?0)???????????????|??/*?6?[cpu_loading]?cur_idle_time[3].time:890438730?cur_wall_time[3].time:1008009950
?*/
?0)???????????????|??/*?6?[cpu_loading]?tmp_cpu_loading:2?prev_cpu_loading:1?previous?state:3
?*/
?0)???????????????|??/*?6?[cpu_loading]?sent?uevent?success:lower=2?*/
?0)???????????????|??/*?6?[cpu_loading]?current?state:3
?*/
?0)???????????????|??/*?6?[cpu_loading]?enable?timer?*/
?1)???1.462?us????|??touch_atime();
?1)???0.616?us????|??touch_atime();
?1)???0.385?us????|??touch_atime();
?1)???0.538?us????|??touch_atime();
?1)???0.539?us????|??touch_atime();
?1)???1.461?us????|??touch_atime();
?1)???0.308?us????|??touch_atime();
?1)???0.385?us????|??touch_atime();
?1)???0.385?us????|??touch_atime();
?1)???2.000?us????|??touch_atime();
?1)???0.923?us????|??touch_atime();
?1)???0.615?us????|??touch_atime();
xxx:/sys/kernel/debug/tracing?#

通過該文件還可以指定屬于特定模塊的函數(shù)，這要用到 mod 指令。指定模塊的格式為：

echo?':mod:[module_name]'?>?set_ftrace_filter

查看對應(yīng)的內(nèi)核模塊

xxx:/sys/kernel/debug/tracing?#?cat?/proc/devices
Character?devices:
??1?mem
??2?pty
??3?ttyp
??4?ttyS
??5?/dev/tty
??5?/dev/console
??5?/dev/ptmx
?10?misc
?13?input
?14?sound
?29?fb

使用過濾器只針對某個(gè)模塊進(jìn)行跟蹤

xxx:/sys/kernel/debug/tracing?#?echo?':mod:sound'?>?set_ftrace_filter
1|xxx:/sys/kernel/debug/tracing?#

需要注意的是，這三種形式不能組合使用，比如“beginmiddleend”實(shí)際的效果與“begin”相同。另外，使用通配符表達(dá)式時(shí)，需要用單引號將其括起來，如果使用雙引號，shell 可能會對字符‘ * ’進(jìn)行擴(kuò)展，這樣最終跟蹤的對象可能與目標(biāo)函數(shù)不一樣。