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Linux ftrace的使用（2）(TODO) 整理自《奔跑吧 Linux内核，张天飞著》1. 动态ftrace在配置内核时打开了CONFIG_DYNAMIC_FTRACE选项，就可以支持动态ftrace功能。set_ftrace_filter和set_ftrace_notrace这两个文件可以配对使用，其中，前者设置要跟踪的函数，后者指定不要跟踪的函数。在实际的调试过程中，我们通常会被ftrace提供的大量信息淹没，因此动态过滤的方法非常有用。avaliable_filter_functions文件可以列出当前系统支持的所有函数，例如现在我只想关注hrtimer_nanosleep()和hrtimer_interrupt()这两个函数。# cd /sys/kernel/debug/tracing # echo hrtimer_nanosleep hrtimer_interrupt > set_ftrace_filter # echo function > current_tracer # echo 1 > tracing_on # usleep 1 # echo 0 > tracing_on # cat trace抓取的数据如下：# tracer: function # # entries-in-buffer/entries-written: 57/57 #P:4 # # _-----=> irqs-off # / _----=> need-resched # | / _---=> hardirq/softirq # || / _--=> preempt-depth # ||| / delay # TASK-PID CPU# |||| TIMESTAMP FUNCTION # | | | |||| | | rcu_preempt-10 [002] d.h2 11073.199551: hrtimer_interrupt <-arch_timer_handler_virt rcu_preempt-10 [002] d.h2 11073.215430: hrtimer_interrupt <-arch_timer_handler_virt rcu_preempt-10 [002] d.h3 11073.235407: hrtimer_interrupt <-arch_timer_handler_virt rcu_preempt-10 [002] d.h2 11074.191632: hrtimer_interrupt <-arch_timer_handler_virt rcu_preempt-10 [000] d.h2 11074.603390: hrtimer_interrupt <-arch_timer_handler_virt rcu_preempt-10 [001] d.h1 11074.719377: hrtimer_interrupt <-arch_timer_handler_virt rcu_preempt-10 [001] d.h1 11074.735375: hrtimer_interrupt <-arch_timer_handler_virt rcu_preempt-10 [001] d.h1 11074.791404: hrtimer_interrupt <-arch_timer_handler_virt rcu_preempt-10 [001] d.h3 11075.828143: hrtimer_interrupt <-arch_timer_handler_virt ......此外，过滤器还支持如下通配符。<match>*：匹配所有match开头的函数*<match>：匹配所有match结尾的函数*<match>*：匹配所有包含match的函数如果跟踪所有"hrtimer"开头的函数，可以"echo \`hrtimer\_*\` > set_ftrace_filter"。还有两个非常有用的操作符，">"表示会覆盖过滤器里的内容；">>"表示新加的函数会增加到过滤器中，但不会覆盖。# echo do_nanosleep > set_ftrace_filter // 往过滤器里写入do_nanosleep # cat set_ftrace_filter do_nanosleep # echo 'hrtimer_*' >> set_ftrace_filter // 追加写入 # cat set_ftrace_filter hrtimer_init_sleeper hrtimer_active hrtimer_reprogram hrtimer_force_reprogram hrtimer_update_softirq_timer hrtimer_run_softirq hrtimer_forward hrtimer_init hrtimer_wakeup hrtimer_start_range_ns hrtimer_try_to_cancel hrtimer_cancel hrtimer_get_next_event hrtimer_next_event_without hrtimer_interrupt hrtimer_run_queues hrtimer_nanosleep do_nanosleep hrtimer_nanosleep_restart # echo '*preempt*' '*lock*' > set_ftrace_notrace // 表示不跟踪包含preempt和lock的函数 # echo > set_ftrace_filter // 向过滤器中输入空字符表示清空过滤器 cat set_ftrace_filter #### all functions enabled ####2. 事件跟踪ftrace里的跟踪机制主要有两种，分别是函数和tracepoint。前者属于"傻瓜式"操作，后者tracepoint可以理解为一个Linux内核中的的占位符函数，内核子系统的开发者通常喜欢利用它来调试。tracepoint可以输出开发者想要的参数、局部变量等信息。tracepoint的位置比较固定，一般都是内核开发者添加上去的，可以把它理解为传统C语言中#if DEBUG部分。如果在运行中没有开启DEBUG，那么是不占用任何系统开销的。在阅读内核代码时经常会遇到以trace_开头的函数,例如CFS调度器里的update_curr()函数。 */ static void update_curr(struct cfs_rq *cfs_rq) { ...... curr->vruntime += calc_delta_fair(delta_exec, curr); update_min_vruntime(cfs_rq); if (entity_is_task(curr)) { struct task_struct *curtask = task_of(curr); trace_sched_stat_runtime(curtask, delta_exec, curr->vruntime); cgroup_account_cputime(curtask, delta_exec); account_group_exec_runtime(curtask, delta_exec); } ...... }update_curr()函数使用了一个sched_stat_runtime的tracepoint，我们可以在avaliable_events文件中查到，把想要跟踪的事件添加到set_event文件中即可，该文件同样支持通配符。# cd /sys/kernel/debug/tracing # cat available_events | grep sched_stat_runtime sched:sched_stat_runtime # echo sched:sched_stat_runtime > set_event # echo 1 > tracing_on # cat trace # echo sched:* > set_event // 支持通配符，跟踪所有sched开头的事件 # echo *:* > set_event // 跟踪系统所有事件输出如下：# tracer: nop # # entries-in-buffer/entries-written: 456/51078 #P:4 # # _-----=> irqs-off # / _----=> need-resched # | / _---=> hardirq/softirq # || / _--=> preempt-depth # ||| / delay # TASK-PID CPU# |||| TIMESTAMP FUNCTION # | | | |||| | | mali-cmar-backe-5672 [002] d..2 5880.987504: sched_stat_runtime: comm=mali-cmar-backe pid=5672 runtime=117420 [ns] vruntime=216701544114 [ns] Colors-5658 [002] d..2 5880.987548: sched_stat_runtime: comm=Colors pid=5658 runtime=50800 [ns] vruntime=216706582321 [ns] mali-cmar-backe-5672 [002] d..2 5880.987621: sched_stat_runtime: comm=mali-cmar-backe pid=5672 runtime=73240 [ns] vruntime=216701590175 [ns] ......另外事件跟踪还支持另外一个强大的功能，可以设定跟踪条件，做到更精细化的设置。每个tracepoint都定义一个format格式，其中定义了该tracepoint支持的域。# cd /sys/kernel/debug/tracing/events/sched/sched_stat_runtime # cat format输出如下:name: sched_stat_runtime ID: 246 format: field:unsigned short common_type; offset:0; size:2; signed:0; field:unsigned char common_flags; offset:2; size:1; signed:0; field:unsigned char common_preempt_count; offset:3; size:1; signed:0; field:int common_pid; offset:4; size:4; signed:1; field:char comm[16]; offset:8; size:16; signed:0; field:pid_t pid; offset:24; size:4; signed:1; field:u64 runtime; offset:32; size:8; signed:0; field:u64 vruntime; offset:40; size:8; signed:0; print fmt: "comm=%s pid=%d runtime=%Lu [ns] vruntime=%Lu [ns]", REC->comm, REC->pid, (unsigned long long)REC->runtime, (unsigned long long)REC->vruntime例如，sched_stat_runtime这个tracepoint支持8个域，前4个是通用域，后4个是该tracepoint支持的域，comm是一个字符串域，其他都是数字域。支持类似C语言表达式对事件进行过滤，对于数字域支持==, !=, <, <=, >, >=, &操作符，对于字符串域支持==, !=, ~操作符。例如只想跟踪进程名字开头为sh的所有进程的sched_stat_runtime事件。# cd /sys/kernel/debug/tracing/events/sched/sched_stat_runtime # echo 'comm ~ "sh*"' > filter // 跟踪所有进程名字开头为sh的 echo 'pid==5658' > filter // 跟踪进程PID为5658的输出如下：# # entries-in-buffer/entries-written: 474/51988245 #P:4 # # _-----=> irqs-off # / _----=> need-resched # | / _---=> hardirq/softirq # || / _--=> preempt-depth # ||| / delay # TASK-PID CPU# |||| TIMESTAMP FUNCTION # | | | |||| | | Colors-5658 [003] d..2 18238.020119: sched_stat_runtime: comm=Colors pid=5658 runtime=1010360 [ns] vruntime=1531587993187 [ns] Colors-5658 [003] dn.2 18238.023648: sched_stat_runtime: comm=Colors pid=5658 runtime=425020 [ns] vruntime=1531588418207 [ns] Colors-5658 [003] dn.2 18238.023837: sched_stat_runtime: comm=Colors pid=5658 runtime=52780 [ns] vruntime=1531588470987 [ns] Colors-5658 [003] dn.2 18238.024666: sched_stat_runtime: comm=Colors pid=5658 runtime=637600 [ns] vruntime=1531589108587 [ns] 3. 添加tracepoint内核各个子系统目前已经有大量的tracepoint，如果觉得这些tracepoint还不满足需求，可以自己手动添加一个，这在实际工作中也是很常用的技巧。还是以CFS
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