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tracing mini-HOWTO: # echo 0 > tracing_on : quick way to disable tracing # echo 1 > tracing_on : quick way to re-enable tracing Important files: trace - The static contents of the buffer To clear the buffer write into this file: echo > trace trace_pipe - A consuming read to see the contents of the buffer current_tracer - function and latency tracers available_tracers - list of configured tracers for current_tracer error_log - error log for failed commands (that support it) buffer_size_kb - view and modify size of per cpu buffer buffer_total_size_kb - view total size of all cpu buffers trace_clock -change the clock used to order events local: Per cpu clock but may not be synced across CPUs global: Synced across CPUs but slows tracing down. counter: Not a clock, but just an increment uptime: Jiffy counter from time of boot perf: Same clock that perf events use x86-tsc: TSC cycle counter timestamp_mode -view the mode used to timestamp events delta: Delta difference against a buffer-wide timestamp absolute: Absolute (standalone) timestamp trace_marker - Writes into this file writes into the kernel buffer trace_marker_raw - Writes into this file writes binary data into the kernel buffer tracing_cpumask - Limit which CPUs to trace instances - Make sub-buffers with: mkdir instances/foo Remove sub-buffer with rmdir trace_options - Set format or modify how tracing happens Disable an option by prefixing 'no' to the option name saved_cmdlines_size - echo command number in here to store comm-pid list available_filter_functions - list of functions that can be filtered on set_ftrace_filter - echo function name in here to only trace these functions accepts: func_full_name or glob-matching-pattern modules: Can select a group via module Format: :mod:<module-name> example: echo :mod:ext3 > set_ftrace_filter triggers: a command to perform when function is hit Format: <function>:<trigger>[:count] trigger: traceon, traceoff enable_event:<system>:<event> disable_event:<system>:<event> stacktrace snapshot dump cpudump example: echo do_fault:traceoff > set_ftrace_filter echo do_trap:traceoff:3 > set_ftrace_filter The first one will disable tracing every time do_fault is hit The second will disable tracing at most 3 times when do_trap is hit The first time do trap is hit and it disables tracing, the counter will decrement to 2. If tracing is already disabled, the counter will not decrement. It only decrements when the trigger did work To remove trigger without count: echo '!<function>:<trigger> > set_ftrace_filter To remove trigger with a count: echo '!<function>:<trigger>:0 > set_ftrace_filter set_ftrace_notrace - echo function name in here to never trace. accepts: func_full_name, func_end, func_begin, func_middle modules: Can select a group via module command :mod: Does not accept triggers set_ftrace_pid - Write pid(s) to only function trace those pids (function) set_graph_function - Trace the nested calls of a function (function_graph) set_graph_notrace - Do not trace the nested calls of a function (function_graph) max_graph_depth - Trace a limited depth of nested calls (0 is unlimited) snapshot - Like 'trace' but shows the content of the static snapshot buffer. Read the contents for more information stack_trace - Shows the max stack trace when active stack_max_size - Shows current max stack size that was traced Write into this file to reset the max size (trigger a new trace) stack_trace_filter - Like set_ftrace_filter but limits what stack_trace traces dynamic_events - Create/append/remove/show the generic dynamic events Write into this file to define/undefine new trace events. kprobe_events - Create/append/remove/show the kernel dynamic events Write into this file to define/undefine new trace events. uprobe_events - Create/append/remove/show the userspace dynamic events Write into this file to define/undefine new trace events. accepts: event-definitions (one definition per line) Format: p[:[<group>/]<event>] <place> [<args>] r[maxactive][:[<group>/]<event>] <place> [<args>] s:[synthetic/]<event> <field> [<field>] -:[<group>/]<event> place: [<module>:]<symbol>[+<offset>]\|<memaddr> place (kretprobe): [<module>:]<symbol>[+<offset>]\|<memaddr> place (uprobe): <path>:<offset>[(ref_ctr_offset)] args: <name>=fetcharg[:type] fetcharg: %<register>, @<address>, @<symbol>[+\|-<offset>], $stack<index>, $stack, $retval, $comm, $arg<N>, +\|-[u]<offset>(<fetcharg>), \imm-value, \"imm-string" type: s8/16/32/64, u8/16/32/64, x8/16/32/64, string, symbol, b<bit-width>@<bit-offset>/<container-size>, ustring, <type>\[<array-size>\] field: <stype> <name>; stype: u8/u16/u32/u64, s8/s16/s32/s64, pid_t, [unsigned] char/int/long events/ - Directory containing all trace event subsystems: enable - Write 0/1 to enable/disable tracing of all events events/<system>/ - Directory containing all trace events for <system>: enable - Write 0/1 to enable/disable tracing of all <system> events filter - If set, only events passing filter are traced events/<system>/<event>/ - Directory containing control files for <event>: enable - Write 0/1 to enable/disable tracing of <event> filter - If set, only events passing filter are traced trigger - If set, a command to perform when event is hit Format: <trigger>[:count][if <filter>] trigger: traceon, traceoff enable_event:<system>:<event> disable_event:<system>:<event> enable_hist:<system>:<event> disable_hist:<system>:<event> stacktrace snapshot hist (see below) example: echo traceoff > events/block/block_unplug/trigger echo traceoff:3 > events/block/block_unplug/trigger echo 'enable_event:kmem:kmalloc:3 if nr_rq > 1' > \ events/block/block_unplug/trigger The first disables tracing every time block_unplug is hit. The second disables tracing the first 3 times block_unplug is hit. The third enables the kmalloc event the first 3 times block_unplug is hit and has value of greater than 1 for the 'nr_rq' event field. Like function triggers, the counter is only decremented if it enabled or disabled tracing. To remove a trigger without a count: echo '!<trigger> > <system>/<event>/trigger To remove a trigger with a count: echo '!<trigger>:0 > <system>/<event>/trigger Filters can be ignored when removing a trigger. hist trigger - If set, event hits are aggregated into a hash table Format: hist:keys=<field1[,field2,...]> [:values=<field1[,field2,...]>] [:sort=<field1[,field2,...]>] [:size=#entries] [:pause][:continue][:clear] [:name=histname1] [:<handler>.<action>] [if <filter>] When a matching event is hit, an entry is added to a hash table using the key(s) and value(s) named, and the value of a sum called 'hitcount' is incremented. Keys and values correspond to fields in the event's format description. Keys can be any field, or the special string 'stacktrace'. Compound keys consisting of up to two fields can be specified by the 'keys' keyword. Values must correspond to numeric fields. Sort keys consisting of up to two fields can be specified using the 'sort' keyword. The sort direction can be modified by appending '.descending' or '.ascending' to a sort field. The 'size' parameter can be used to specify more or fewer than the default 2048 entries for the hashtable size. If a hist trigger is given a name using the 'name' parameter, its histogram data will be shared with other triggers of the same name, and trigger hits will update this common data. Reading the 'hist' file for the event will dump the hash table in its entirety to stdout. If there are multiple hist triggers attached to an event, there will be a table for each trigger in the output. The table displayed for a named trigger will be the same as any other instance having the same name. The default format used to display a given field can be modified by appending any of the following modifiers to the field name, as applicable: .hex display a number as a hex value .sym display an address as a symbol .sym-offset display an address as a symbol and offset .execname display a common_pid as a program name .syscall display a syscall id as a syscall name .log2 display log2 value rather than raw number .usecs display a common_timestamp in microseconds The 'pause' parameter can be used to pause an existing hist trigger or to start a hist trigger but not log any events until told to do so. 'continue' can be used to start or restart a paused hist trigger. The 'clear' parameter will clear the contents of a running hist trigger and leave its current paused/active state unchanged. The enable_hist and disable_hist triggers can be used to have one event conditionally start and stop another event's already-attached hist trigger. The syntax is analogous to the enable_event and disable_event triggers. Hist trigger handlers and actions are executed whenever a a histogram entry is added or updated. They take the form: <handler>.<action> The available handlers are: onmatch(matching.event) - invoke on addition or update onmax(var) - invoke if var exceeds current max onchange(var) - invoke action if var changes The available actions are: trace(<synthetic_event>,param list) - generate synthetic event save(field,...) - save current event fields snapshot() - snapshot the trace buffer

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