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Diffstat (limited to 'Documentation/trace/ftrace.txt')
| -rw-r--r-- | Documentation/trace/ftrace.txt | 252 |
1 files changed, 156 insertions, 96 deletions
diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt index fd9a3e6..a39b3c7 100644 --- a/Documentation/trace/ftrace.txt +++ b/Documentation/trace/ftrace.txt @@ -7,7 +7,6 @@ Copyright 2008 Red Hat Inc. (dual licensed under the GPL v2) Reviewers: Elias Oltmanns, Randy Dunlap, Andrew Morton, John Kacur, and David Teigland. - Written for: 2.6.28-rc2 Introduction @@ -33,13 +32,26 @@ The File System Ftrace uses the debugfs file system to hold the control files as well as the files to display output. -To mount the debugfs system: +When debugfs is configured into the kernel (which selecting any ftrace +option will do) the directory /sys/kernel/debug will be created. To mount +this directory, you can add to your /etc/fstab file: + + debugfs /sys/kernel/debug debugfs defaults 0 0 + +Or you can mount it at run time with: + + mount -t debugfs nodev /sys/kernel/debug - # mkdir /debug - # mount -t debugfs nodev /debug +For quicker access to that directory you may want to make a soft link to +it: -( Note: it is more common to mount at /sys/kernel/debug, but for - simplicity this document will use /debug) + ln -s /sys/kernel/debug /debug + +Any selected ftrace option will also create a directory called tracing +within the debugfs. The rest of the document will assume that you are in +the ftrace directory (cd /sys/kernel/debug/tracing) and will only concentrate +on the files within that directory and not distract from the content with +the extended "/sys/kernel/debug/tracing" path name. That's it! (assuming that you have ftrace configured into your kernel) @@ -179,7 +191,7 @@ Here is the list of current tracers that may be configured. Function call tracer to trace all kernel functions. - "function_graph_tracer" + "function_graph" Similar to the function tracer except that the function tracer probes the functions on their entry @@ -389,18 +401,18 @@ trace_options The trace_options file is used to control what gets printed in the trace output. To see what is available, simply cat the file: - cat /debug/tracing/trace_options + cat trace_options print-parent nosym-offset nosym-addr noverbose noraw nohex nobin \ noblock nostacktrace nosched-tree nouserstacktrace nosym-userobj To disable one of the options, echo in the option prepended with "no". - echo noprint-parent > /debug/tracing/trace_options + echo noprint-parent > trace_options To enable an option, leave off the "no". - echo sym-offset > /debug/tracing/trace_options + echo sym-offset > trace_options Here are the available options: @@ -476,11 +488,11 @@ sched_switch This tracer simply records schedule switches. Here is an example of how to use it. - # echo sched_switch > /debug/tracing/current_tracer - # echo 1 > /debug/tracing/tracing_enabled + # echo sched_switch > current_tracer + # echo 1 > tracing_enabled # sleep 1 - # echo 0 > /debug/tracing/tracing_enabled - # cat /debug/tracing/trace + # echo 0 > tracing_enabled + # cat trace # tracer: sched_switch # @@ -518,9 +530,18 @@ 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 priority: 0 to 99 ==> user RT priority 99 to 0 - Kernel priority: 100 to 139 ==> user nice -20 to 19 - Kernel priority: 140 ==> idle task priority + 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: @@ -574,13 +595,13 @@ new trace is saved. To reset the maximum, echo 0 into tracing_max_latency. Here is an example: - # echo irqsoff > /debug/tracing/current_tracer - # echo 0 > /debug/tracing/tracing_max_latency - # echo 1 > /debug/tracing/tracing_enabled + # echo irqsoff > current_tracer + # echo 0 > tracing_max_latency + # echo 1 > tracing_enabled # ls -ltr [...] - # echo 0 > /debug/tracing/tracing_enabled - # cat /debug/tracing/latency_trace + # echo 0 > tracing_enabled + # cat latency_trace # tracer: irqsoff # irqsoff latency trace v1.1.5 on 2.6.26 @@ -681,13 +702,13 @@ Like the irqsoff tracer, it records the maximum latency for which preemption was disabled. The control of preemptoff tracer is much like the irqsoff tracer. - # echo preemptoff > /debug/tracing/current_tracer - # echo 0 > /debug/tracing/tracing_max_latency - # echo 1 > /debug/tracing/tracing_enabled + # echo preemptoff > current_tracer + # echo 0 > tracing_max_latency + # echo 1 > tracing_enabled # ls -ltr [...] - # echo 0 > /debug/tracing/tracing_enabled - # cat /debug/tracing/latency_trace + # echo 0 > tracing_enabled + # cat latency_trace # tracer: preemptoff # preemptoff latency trace v1.1.5 on 2.6.26-rc8 @@ -828,13 +849,13 @@ tracer. Again, using this trace is much like the irqsoff and preemptoff tracers. - # echo preemptirqsoff > /debug/tracing/current_tracer - # echo 0 > /debug/tracing/tracing_max_latency - # echo 1 > /debug/tracing/tracing_enabled + # echo preemptirqsoff > current_tracer + # echo 0 > tracing_max_latency + # echo 1 > tracing_enabled # ls -ltr [...] - # echo 0 > /debug/tracing/tracing_enabled - # cat /debug/tracing/latency_trace + # echo 0 > tracing_enabled + # cat latency_trace # tracer: preemptirqsoff # preemptirqsoff latency trace v1.1.5 on 2.6.26-rc8 @@ -990,12 +1011,12 @@ slightly differently than we did with the previous tracers. Instead of performing an 'ls', we will run 'sleep 1' under 'chrt' which changes the priority of the task. - # echo wakeup > /debug/tracing/current_tracer - # echo 0 > /debug/tracing/tracing_max_latency - # echo 1 > /debug/tracing/tracing_enabled + # echo wakeup > current_tracer + # echo 0 > tracing_max_latency + # echo 1 > tracing_enabled # chrt -f 5 sleep 1 - # echo 0 > /debug/tracing/tracing_enabled - # cat /debug/tracing/latency_trace + # echo 0 > tracing_enabled + # cat latency_trace # tracer: wakeup # wakeup latency trace v1.1.5 on 2.6.26-rc8 @@ -1105,11 +1126,11 @@ can be done from the debug file system. Make sure the ftrace_enabled is set; otherwise this tracer is a nop. # sysctl kernel.ftrace_enabled=1 - # echo function > /debug/tracing/current_tracer - # echo 1 > /debug/tracing/tracing_enabled + # echo function > current_tracer + # echo 1 > tracing_enabled # usleep 1 - # echo 0 > /debug/tracing/tracing_enabled - # cat /debug/tracing/trace + # echo 0 > tracing_enabled + # cat trace # tracer: function # # TASK-PID CPU# TIMESTAMP FUNCTION @@ -1146,7 +1167,7 @@ int trace_fd; [...] int main(int argc, char *argv[]) { [...] - trace_fd = open("/debug/tracing/tracing_enabled", O_WRONLY); + trace_fd = open(tracing_file("tracing_enabled"), O_WRONLY); [...] if (condition_hit()) { write(trace_fd, "0", 1); @@ -1154,26 +1175,20 @@ int main(int argc, char *argv[]) { [...] } -Note: Here we hard coded the path name. The debugfs mount is not -guaranteed to be at /debug (and is more commonly at -/sys/kernel/debug). For simple one time traces, the above is -sufficent. For anything else, a search through /proc/mounts may -be needed to find where the debugfs file-system is mounted. - Single thread tracing --------------------- -By writing into /debug/tracing/set_ftrace_pid you can trace a +By writing into set_ftrace_pid you can trace a single thread. For example: -# cat /debug/tracing/set_ftrace_pid +# cat set_ftrace_pid no pid -# echo 3111 > /debug/tracing/set_ftrace_pid -# cat /debug/tracing/set_ftrace_pid +# echo 3111 > set_ftrace_pid +# cat set_ftrace_pid 3111 -# echo function > /debug/tracing/current_tracer -# cat /debug/tracing/trace | head +# echo function > current_tracer +# cat trace | head # tracer: function # # TASK-PID CPU# TIMESTAMP FUNCTION @@ -1184,8 +1199,8 @@ no pid yum-updatesd-3111 [003] 1637.254683: lock_hrtimer_base <-hrtimer_try_to_cancel yum-updatesd-3111 [003] 1637.254685: fget_light <-do_sys_poll yum-updatesd-3111 [003] 1637.254686: pipe_poll <-do_sys_poll -# echo -1 > /debug/tracing/set_ftrace_pid -# cat /debug/tracing/trace |head +# echo -1 > set_ftrace_pid +# cat trace |head # tracer: function # # TASK-PID CPU# TIMESTAMP FUNCTION @@ -1207,6 +1222,51 @@ something like this simple program: #include <fcntl.h> #include <unistd.h> +#define _STR(x) #x +#define STR(x) _STR(x) +#define MAX_PATH 256 + +const char *find_debugfs(void) +{ + static char debugfs[MAX_PATH+1]; + static int debugfs_found; + char type[100]; + FILE *fp; + + if (debugfs_found) + return debugfs; + + if ((fp = fopen("/proc/mounts","r")) == NULL) { + perror("/proc/mounts"); + return NULL; + } + + while (fscanf(fp, "%*s %" + STR(MAX_PATH) + "s %99s %*s %*d %*d\n", + debugfs, type) == 2) { + if (strcmp(type, "debugfs") == 0) + break; + } + fclose(fp); + + if (strcmp(type, "debugfs") != 0) { + fprintf(stderr, "debugfs not mounted"); + return NULL; + } + + debugfs_found = 1; + + return debugfs; +} + +const char *tracing_file(const char *file_name) +{ + static char trace_file[MAX_PATH+1]; + snprintf(trace_file, MAX_PATH, "%s/%s", find_debugfs(), file_name); + return trace_file; +} + int main (int argc, char **argv) { if (argc < 1) @@ -1217,12 +1277,12 @@ int main (int argc, char **argv) char line[64]; int s; - ffd = open("/debug/tracing/current_tracer", O_WRONLY); + ffd = open(tracing_file("current_tracer"), O_WRONLY); if (ffd < 0) exit(-1); write(ffd, "nop", 3); - fd = open("/debug/tracing/set_ftrace_pid", O_WRONLY); + fd = open(tracing_file("set_ftrace_pid"), O_WRONLY); s = sprintf(line, "%d\n", getpid()); write(fd, line, s); @@ -1374,22 +1434,22 @@ want, depending on your needs. tracing_cpu_mask file) or you might sometimes see unordered function calls while cpu tracing switch. - hide: echo nofuncgraph-cpu > /debug/tracing/trace_options - show: echo funcgraph-cpu > /debug/tracing/trace_options + hide: echo nofuncgraph-cpu > trace_options + show: echo funcgraph-cpu > trace_options - The duration (function's time of execution) is displayed on the closing bracket line of a function or on the same line than the current function in case of a leaf one. It is default enabled. - hide: echo nofuncgraph-duration > /debug/tracing/trace_options - show: echo funcgraph-duration > /debug/tracing/trace_options + hide: echo nofuncgraph-duration > trace_options + show: echo funcgraph-duration > trace_options - The overhead field precedes the duration field in case of reached duration thresholds. - hide: echo nofuncgraph-overhead > /debug/tracing/trace_options - show: echo funcgraph-overhead > /debug/tracing/trace_options + hide: echo nofuncgraph-overhead > trace_options + show: echo funcgraph-overhead > trace_options depends on: funcgraph-duration ie: @@ -1418,8 +1478,8 @@ want, depending on your needs. - The task/pid field displays the thread cmdline and pid which executed the function. It is default disabled. - hide: echo nofuncgraph-proc > /debug/tracing/trace_options - show: echo funcgraph-proc > /debug/tracing/trace_options + hide: echo nofuncgraph-proc > trace_options + show: echo funcgraph-proc > trace_options ie: @@ -1442,8 +1502,8 @@ want, depending on your needs. system clock since it started. A snapshot of this time is given on each entry/exit of functions - hide: echo nofuncgraph-abstime > /debug/tracing/trace_options - show: echo funcgraph-abstime > /debug/tracing/trace_options + hide: echo nofuncgraph-abstime > trace_options + show: echo funcgraph-abstime > trace_options ie: @@ -1540,7 +1600,7 @@ listed in: available_filter_functions - # cat /debug/tracing/available_filter_functions + # cat available_filter_functions put_prev_task_idle kmem_cache_create pick_next_task_rt @@ -1552,12 +1612,12 @@ mutex_lock If I am only interested in sys_nanosleep and hrtimer_interrupt: # echo sys_nanosleep hrtimer_interrupt \ - > /debug/tracing/set_ftrace_filter - # echo ftrace > /debug/tracing/current_tracer - # echo 1 > /debug/tracing/tracing_enabled + > set_ftrace_filter + # echo ftrace > current_tracer + # echo 1 > tracing_enabled # usleep 1 - # echo 0 > /debug/tracing/tracing_enabled - # cat /debug/tracing/trace + # echo 0 > tracing_enabled + # cat trace # tracer: ftrace # # TASK-PID CPU# TIMESTAMP FUNCTION @@ -1568,7 +1628,7 @@ If I am only interested in sys_nanosleep and hrtimer_interrupt: To see which functions are being traced, you can cat the file: - # cat /debug/tracing/set_ftrace_filter + # cat set_ftrace_filter hrtimer_interrupt sys_nanosleep @@ -1588,7 +1648,7 @@ Note: It is better to use quotes to enclose the wild cards, otherwise the shell may expand the parameters into names of files in the local directory. - # echo 'hrtimer_*' > /debug/tracing/set_ftrace_filter + # echo 'hrtimer_*' > set_ftrace_filter Produces: @@ -1609,7 +1669,7 @@ Produces: Notice that we lost the sys_nanosleep. - # cat /debug/tracing/set_ftrace_filter + # cat set_ftrace_filter hrtimer_run_queues hrtimer_run_pending hrtimer_init @@ -1635,17 +1695,17 @@ To append to the filters, use '>>' To clear out a filter so that all functions will be recorded again: - # echo > /debug/tracing/set_ftrace_filter - # cat /debug/tracing/set_ftrace_filter + # echo > set_ftrace_filter + # cat set_ftrace_filter # Again, now we want to append. - # echo sys_nanosleep > /debug/tracing/set_ftrace_filter - # cat /debug/tracing/set_ftrace_filter + # echo sys_nanosleep > set_ftrace_filter + # cat set_ftrace_filter sys_nanosleep - # echo 'hrtimer_*' >> /debug/tracing/set_ftrace_filter - # cat /debug/tracing/set_ftrace_filter + # echo 'hrtimer_*' >> set_ftrace_filter + # cat set_ftrace_filter hrtimer_run_queues hrtimer_run_pending hrtimer_init @@ -1668,7 +1728,7 @@ hrtimer_init_sleeper The set_ftrace_notrace prevents those functions from being traced. - # echo '*preempt*' '*lock*' > /debug/tracing/set_ftrace_notrace + # echo '*preempt*' '*lock*' > set_ftrace_notrace Produces: @@ -1758,13 +1818,13 @@ the effect on the tracing is different. Every read from trace_pipe is consumed. This means that subsequent reads will be different. The trace is live. - # echo function > /debug/tracing/current_tracer - # cat /debug/tracing/trace_pipe > /tmp/trace.out & + # echo function > current_tracer + # cat trace_pipe > /tmp/trace.out & [1] 4153 - # echo 1 > /debug/tracing/tracing_enabled + # echo 1 > tracing_enabled # usleep 1 - # echo 0 > /debug/tracing/tracing_enabled - # cat /debug/tracing/trace + # echo 0 > tracing_enabled + # cat trace # tracer: function # # TASK-PID CPU# TIMESTAMP FUNCTION @@ -1800,7 +1860,7 @@ number listed is the number of entries that can be recorded per CPU. To know the full size, multiply the number of possible CPUS with the number of entries. - # cat /debug/tracing/buffer_size_kb + # cat buffer_size_kb 1408 (units kilobytes) Note, to modify this, you must have tracing completely disabled. @@ -1808,21 +1868,21 @@ To do that, echo "nop" into the current_tracer. If the current_tracer is not set to "nop", an EINVAL error will be returned. - # echo nop > /debug/tracing/current_tracer - # echo 10000 > /debug/tracing/buffer_size_kb - # cat /debug/tracing/buffer_size_kb + # echo nop > current_tracer + # echo 10000 > buffer_size_kb + # cat buffer_size_kb 10000 (units kilobytes) The number of pages which will be allocated is limited to a percentage of available memory. Allocating too much will produce an error. - # echo 1000000000000 > /debug/tracing/buffer_size_kb + # echo 1000000000000 > buffer_size_kb -bash: echo: write error: Cannot allocate memory - # cat /debug/tracing/buffer_size_kb + # cat buffer_size_kb 85 ----------- More details can be found in the source code, in the -kernel/tracing/*.c files. +kernel/trace/*.c files. |
