在tracefs跟踪目录中有一个名为“instances”的目录。
使用mkdir可以在这个目录中创建新的目录，使用rmdir可以删除目录。在这个目录中使用mkdir创建的目录在创建之后已经包含了文件和其他目录:
[root@idle tracing]# mkdir instances/idle
[root@idle tracing]# ls instances/idle/
available_tracers per_cpu trace_clock
buffer_percent set_event trace_marker
buffer_size_kb set_event_pid trace_marker_raw
buffer_total_size_kb set_ftrace_filter trace_options
current_tracer set_ftrace_notrace trace_pipe
error_log set_ftrace_pid tracing_cpumask
events snapshot tracing_max_latency
free_buffer timestamp_mode tracing_on
options trace
[root@idle tracing]# cat instances/idle/buffer_size_kb
1410
新目录中的文件与原tracing目录中同名的文件的工作方式相同，只是所使用的缓冲区是一个单独的新缓冲区。这些文件会影响该缓冲区，但不会影响主缓冲区。
当前我们使用的内核版本linux5.0，已经有current_tracer和available_tracers，可以使用function tracer，但是不支持function_graph。
[root@idle tracing]# cat available_tracers
function_graph wakeup_dl wakeup_rt wakeup preemptirqsoff preemptoff irqsoff function nop
[root@idle tracing]# mkdir instances/idle
[root@idle tracing]# cat instances/idle/available_tracers
wakeup_dl wakeup_rt wakeup preemptirqsoff preemptoff irqsoff function nop
下面举例说明instances如何使用：
cd /sys/kernel/debug/tracing/
echo 0 > tracing_on
echo 0 > trace
echo function > current_tracer
echo vfs_open > ./set_ftrace_filter
echo 1 > ./options/func_stack_trace
mkdir instances/sched
echo 1 > instances/sched/events/sched/sched_wakeup/enable
mkdir instances/syscall
echo 1 > instances/syscall/events/syscalls/sys_enter_read/enable
echo 1 > instances/syscall/events/syscalls/sys_enter_readlinkat/enable
echo 1 > tracing_on
cat /mnt/ftrace_script/function/test.file
echo 0 > tracing_on
cat trace
cat instances/sched/trace
cat instances/syscall/trace
echo nop > ./current_tracer
echo 0 > ./options/func_stack_trace
echo !vfs_open >> ./set_ftrace_filter
echo 0 > trace
rmdir instances/sched
rmdir instances/syscall
tracer: function
#
# entries-in-buffer/entries-written: 40/40 #P:4
#
# _-----=> irqs-off
# / _----=> need-resched
# | / _---=> hardirq/softirq
# || / _--=> preempt-depth
# ||| / delay
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
# | | | |||| | |
cat-769 [002] .... 2286.434048: vfs_open <-do_last
cat-769 [002] .... 2286.434125: <stack trace>
=> vfs_open
=> path_openat
=> do_filp_open
=> do_open_execat
=> __do_execve_file
=> do_execveat_common
=> do_execve
=> __se_sys_execve
=> __arm64_sys_execve
=> __invoke_syscall
=> invoke_syscall
=> el0_svc_common
=> el0_svc_handler
=> el0_svc
cat-769 [002] .... 2286.437829: vfs_open <-do_last
# tracer: nop
#
# entries-in-buffer/entries-written: 155/155 #P:4
#
# _-----=> irqs-off
# / _----=> need-resched
# | / _---=> hardirq/softirq
# || / _--=> preempt-depth
# ||| / delay
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
# | | | |||| | |
<idle>-0 [003] dNs. 2285.484852: sched_wakeup: comm=rcu_sched pid=10 prio=120 tar
get_cpu=003
<idle>-0 [003] dNs. 2285.500782: sched_wakeup: comm=rcu_sched pid=10 prio=120 tar
get_cpu=003
<idle>-0 [003] dNs. 2285.532258: sched_wakeup: comm=rcu_sched pid=10 prio=120 tar
get_cpu=003
<idle>-0 [000] dNs. 2285.539682: sched_wakeup: comm=ksoftirqd/0 pid=9 prio=120 ta
rget_cpu=000
# tracer: nop
#
# entries-in-buffer/entries-written: 18/18 #P:4
#
# _-----=> irqs-off
# / _----=> need-resched
# | / _---=> hardirq/softirq
# || / _--=> preempt-depth
# ||| / delay
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
# | | | |||| | |
cat-769 [002] .... 2286.472346: sys_read(fd: 3, buf: ffffef106c00, count: 340)
cat-769 [002] .... 2286.574676: sys_read(fd: 3, buf: ffff9a9ae000, count: 20000)
cat-769 [002] .... 2286.591041: sys_read(fd: 3, buf: ffff9a9ae000, count: 20000)
bash-766 [001] .... 2286.663201: sys_read(fd: fe, buf: aaab09e06310, count: 2dd)
<...>-770 [002] .... 2286.787743: sys_read(fd: 3, buf: ffffc0ff16d0, count: 340)
