diff options
Diffstat (limited to 'Documentation/trace/ftrace.txt')
| -rw-r--r-- | Documentation/trace/ftrace.txt | 151 |
1 files changed, 23 insertions, 128 deletions
diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt index 557c1edecca..1ebc24cf9a5 100644 --- a/Documentation/trace/ftrace.txt +++ b/Documentation/trace/ftrace.txt @@ -80,11 +80,11 @@ of ftrace. Here is a list of some of the key files: tracers listed here can be configured by echoing their name into current_tracer. - tracing_enabled: + tracing_on: - This sets or displays whether the current_tracer - is activated and tracing or not. Echo 0 into this - file to disable the tracer or 1 to enable it. + This sets or displays whether writing to the trace + ring buffer is enabled. Echo 0 into this file to disable + the tracer or 1 to enable it. trace: @@ -202,10 +202,6 @@ Here is the list of current tracers that may be configured. to draw a graph of function calls similar to C code source. - "sched_switch" - - Traces the context switches and wakeups between tasks. - "irqsoff" Traces the areas that disable interrupts and saves @@ -273,39 +269,6 @@ format, the function name that was traced "path_put" and the parent function that called this function "path_walk". The timestamp is the time at which the function was entered. -The sched_switch tracer also includes tracing of task wakeups -and context switches. - - ksoftirqd/1-7 [01] 1453.070013: 7:115:R + 2916:115:S - ksoftirqd/1-7 [01] 1453.070013: 7:115:R + 10:115:S - ksoftirqd/1-7 [01] 1453.070013: 7:115:R ==> 10:115:R - events/1-10 [01] 1453.070013: 10:115:S ==> 2916:115:R - kondemand/1-2916 [01] 1453.070013: 2916:115:S ==> 7:115:R - ksoftirqd/1-7 [01] 1453.070013: 7:115:S ==> 0:140:R - -Wake ups are represented by a "+" and the context switches are -shown as "==>". The format is: - - Context switches: - - Previous task Next Task - - <pid>:<prio>:<state> ==> <pid>:<prio>:<state> - - Wake ups: - - Current task Task waking up - - <pid>:<prio>:<state> + <pid>:<prio>:<state> - -The prio is the internal kernel priority, which is the inverse -of the priority that is usually displayed by user-space tools. -Zero represents the highest priority (99). Prio 100 starts the -"nice" priorities with 100 being equal to nice -20 and 139 being -nice 19. The prio "140" is reserved for the idle task which is -the lowest priority thread (pid 0). - - Latency trace format -------------------- @@ -491,78 +454,10 @@ x494] <- /root/a.out[+0x4a8] <- /lib/libc-2.7.so[+0x1e1a6] latencies, as described in "Latency trace format". -sched_switch ------------- - -This tracer simply records schedule switches. Here is an example -of how to use it. - - # echo sched_switch > current_tracer - # echo 1 > tracing_enabled - # sleep 1 - # echo 0 > tracing_enabled - # cat trace - -# tracer: sched_switch -# -# TASK-PID CPU# TIMESTAMP FUNCTION -# | | | | | - bash-3997 [01] 240.132281: 3997:120:R + 4055:120:R - bash-3997 [01] 240.132284: 3997:120:R ==> 4055:120:R - sleep-4055 [01] 240.132371: 4055:120:S ==> 3997:120:R - bash-3997 [01] 240.132454: 3997:120:R + 4055:120:S - bash-3997 [01] 240.132457: 3997:120:R ==> 4055:120:R - sleep-4055 [01] 240.132460: 4055:120:D ==> 3997:120:R - bash-3997 [01] 240.132463: 3997:120:R + 4055:120:D - bash-3997 [01] 240.132465: 3997:120:R ==> 4055:120:R - <idle>-0 [00] 240.132589: 0:140:R + 4:115:S - <idle>-0 [00] 240.132591: 0:140:R ==> 4:115:R - ksoftirqd/0-4 [00] 240.132595: 4:115:S ==> 0:140:R - <idle>-0 [00] 240.132598: 0:140:R + 4:115:S - <idle>-0 [00] 240.132599: 0:140:R ==> 4:115:R - ksoftirqd/0-4 [00] 240.132603: 4:115:S ==> 0:140:R - sleep-4055 [01] 240.133058: 4055:120:S ==> 3997:120:R - [...] - - -As we have discussed previously about this format, the header -shows the name of the trace and points to the options. The -"FUNCTION" is a misnomer since here it represents the wake ups -and context switches. - -The sched_switch file only lists the wake ups (represented with -'+') and context switches ('==>') with the previous task or -current task first followed by the next task or task waking up. -The format for both of these is PID:KERNEL-PRIO:TASK-STATE. -Remember that the KERNEL-PRIO is the inverse of the actual -priority with zero (0) being the highest priority and the nice -values starting at 100 (nice -20). Below is a quick chart to map -the kernel priority to user land priorities. - - Kernel Space User Space - =============================================================== - 0(high) to 98(low) user RT priority 99(high) to 1(low) - with SCHED_RR or SCHED_FIFO - --------------------------------------------------------------- - 99 sched_priority is not used in scheduling - decisions(it must be specified as 0) - --------------------------------------------------------------- - 100(high) to 139(low) user nice -20(high) to 19(low) - --------------------------------------------------------------- - 140 idle task priority - --------------------------------------------------------------- - -The task states are: - - R - running : wants to run, may not actually be running - S - sleep : process is waiting to be woken up (handles signals) - D - disk sleep (uninterruptible sleep) : process must be woken up - (ignores signals) - T - stopped : process suspended - t - traced : process is being traced (with something like gdb) - Z - zombie : process waiting to be cleaned up - X - unknown - + overwrite - This controls what happens when the trace buffer is + full. If "1" (default), the oldest events are + discarded and overwritten. If "0", then the newest + events are discarded. ftrace_enabled -------------- @@ -607,10 +502,10 @@ an example: # echo irqsoff > current_tracer # echo latency-format > trace_options # echo 0 > tracing_max_latency - # echo 1 > tracing_enabled + # echo 1 > tracing_on # ls -ltr [...] - # echo 0 > tracing_enabled + # echo 0 > tracing_on # cat trace # tracer: irqsoff # @@ -715,10 +610,10 @@ is much like the irqsoff tracer. # echo preemptoff > current_tracer # echo latency-format > trace_options # echo 0 > tracing_max_latency - # echo 1 > tracing_enabled + # echo 1 > tracing_on # ls -ltr [...] - # echo 0 > tracing_enabled + # echo 0 > tracing_on # cat trace # tracer: preemptoff # @@ -863,10 +758,10 @@ tracers. # echo preemptirqsoff > current_tracer # echo latency-format > trace_options # echo 0 > tracing_max_latency - # echo 1 > tracing_enabled + # echo 1 > tracing_on # ls -ltr [...] - # echo 0 > tracing_enabled + # echo 0 > tracing_on # cat trace # tracer: preemptirqsoff # @@ -1026,9 +921,9 @@ Instead of performing an 'ls', we will run 'sleep 1' under # echo wakeup > current_tracer # echo latency-format > trace_options # echo 0 > tracing_max_latency - # echo 1 > tracing_enabled + # echo 1 > tracing_on # chrt -f 5 sleep 1 - # echo 0 > tracing_enabled + # echo 0 > tracing_on # cat trace # tracer: wakeup # @@ -1140,9 +1035,9 @@ ftrace_enabled is set; otherwise this tracer is a nop. # sysctl kernel.ftrace_enabled=1 # echo function > current_tracer - # echo 1 > tracing_enabled + # echo 1 > tracing_on # usleep 1 - # echo 0 > tracing_enabled + # echo 0 > tracing_on # cat trace # tracer: function # @@ -1180,7 +1075,7 @@ int trace_fd; [...] int main(int argc, char *argv[]) { [...] - trace_fd = open(tracing_file("tracing_enabled"), O_WRONLY); + trace_fd = open(tracing_file("tracing_on"), O_WRONLY); [...] if (condition_hit()) { write(trace_fd, "0", 1); @@ -1631,9 +1526,9 @@ If I am only interested in sys_nanosleep and hrtimer_interrupt: # echo sys_nanosleep hrtimer_interrupt \ > set_ftrace_filter # echo function > current_tracer - # echo 1 > tracing_enabled + # echo 1 > tracing_on # usleep 1 - # echo 0 > tracing_enabled + # echo 0 > tracing_on # cat trace # tracer: ftrace # @@ -1879,9 +1774,9 @@ different. The trace is live. # echo function > current_tracer # cat trace_pipe > /tmp/trace.out & [1] 4153 - # echo 1 > tracing_enabled + # echo 1 > tracing_on # usleep 1 - # echo 0 > tracing_enabled + # echo 0 > tracing_on # cat trace # tracer: function # |