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trace-cmd-record(1) [centos man page]

TRACE-CMD-RECORD(1)													       TRACE-CMD-RECORD(1)

trace-cmd-record - record a trace from the Ftrace Linux internal tracer SYNOPSIS
trace-cmd record [OPTIONS] [command] DESCRIPTION
The trace-cmd(1) record command will set up the Ftrace Linux kernel tracer to record the specified plugins or events that happen while the command executes. If no command is given, then it will record until the user hits Ctrl-C. The record command of trace-cmd will set up the Ftrace tracer to start tracing the various events or plugins that are given on the command line. It will then create a number of tracing processes (one per CPU) that will start recording from the kernel ring buffer straight into temporary files. When the command is complete (or Ctrl-C is hit) all the files will be combined into a trace.dat file that can later be read (see trace-cmd-report(1)). OPTIONS
-p plugin Specify a trace plugin. Plugins are special Ftrace tracers that usually do more than just trace an event. Common plugins are function, function_graph, preemptirqsoff, irqsoff, preemptoff, and wakeup. A plugin must be supported by the running kernel. To see a list of available plugins, see trace-cmd-list(1). -e event Specify an event to trace. Various static trace points have been added to the Linux kernel. They are grouped by subsystem where you can enable all events of a given subsystem or specify specific events to be enabled. The event is of the format "subsystem:event-name". You can also just specify the subsystem without the :event-name or the event-name without the "subsystem:". Using "-e sched_switch" will enable the "sched_switch" event where as, "-e sched" will enable all events under the "sched" subsystem. The 'event' can also contain glob expressions. That is, "*stat*" will select all events (or subsystems) that have the characters "stat" in their names. The keyword 'all' can be used to enable all events. -a Every event that is being recorded has its output format file saved in the output file to be able to display it later. But if other events are enabled in the trace without trace-cmd's knowledge, the formats of those events will not be recorded and trace-cmd report will not be able to display them. If this is the case, then specify the -a option and the format for all events in the system will be saved. -T Enable a stacktrace on each event. For example: <idle>-0 [003] 58549.289091: sched_switch: kworker/0:1:0 [120] R ==> trace-cmd:2603 [120] <idle>-0 [003] 58549.289092: kernel_stack: <stack trace> => schedule (ffffffff814b260e) => cpu_idle (ffffffff8100a38c) => start_secondary (ffffffff814ab828) --func-stack Enable a stack trace on all functions. Note this is only applicable for the "function" plugin tracer, and will only take effect if the -l option is used and succeeds in limiting functions. If the function tracer is not filtered, and the stack trace is enabled, you can live lock the machine. -f filter Specify a filter for the previous event. This must come after a -e. This will filter what events get recorded based on the content of the event. Filtering is passed to the kernel directly so what filtering is allowed may depend on what version of the kernel you have. Basically, it will let you use C notation to check if an event should be processed or not. ==, >=, <=, >, <, &, |, && and || The above are usually safe to use to compare fields. -v This will cause all events specified after it on the command line to not be traced. This is useful for selecting a subsystem to be traced but to leave out various events. For Example: "-e sched -v -e "*stat*"" will enable all events in the sched subsystem except those that have "stat" in their names. Note: the *-v* option was taken from the way grep(1) inverts the following matches. -F This will filter only the executable that is given on the command line. If no command is given, then it will filter itself (pretty pointless). Using -F will let you trace only events that are caused by the given command. -P pid Similar to -F but lets you specify a process ID to trace. -c Used with either -F to trace the process' children too. -o output-file By default, trace-cmd report will create a trace.dat file. You can specify a different file to write to with the -o option. -l function-name This will limit the function and function_graph tracers to only trace the given function name. More than one -l may be specified on the command line to trace more than one function. The limited use of glob expressions are also allowed. These are match* to only filter functions that start with match. *match to only filter functions that end with match. *match* to only filter on functions that contain match. -g function-name This option is for the function_graph plugin. It will graph the given function. That is, it will only trace the function and all functions that it calls. You can have more than one -g on the command line. -n function-name This has the opposite effect of -l. The function given with the -n option will not be traced. This takes precedence, that is, if you include the same function for both -n and -l, it will not be traced. -d Some tracer plugins enable the function tracer by default. Like the latency tracers. This option prevents the function tracer from being enabled at start up. -O option Ftrace has various options that can be enabled or disabled. This allows you to set them. Appending the text no to an option disables it. For example: "-O nograph-time" will disable the "graph-time" Ftrace option. -s interval The processes that trace-cmd creates to record from the ring buffer need to wake up to do the recording. Setting the interval to zero will cause the processes to wakeup every time new data is written into the buffer. But since Ftrace is recording kernel activity, the act of this processes going back to sleep may cause new events into the ring buffer which will wake the process back up. This will needlessly add extra data into the ring buffer. The 'interval' metric is microseconds. The default is set to 1000 (1 ms). This is the time each recording process will sleep before waking up to record any new data that was written to the ring buffer. -r priority The priority to run the capture threads at. In a busy system the trace capturing threads may be staved and events can be lost. This increases the priority of those threads to the real time (FIFO) priority. But use this option with care, it can also change the behaviour of the system being traced. -b size This sets the ring buffer size to size kilobytes. Because the Ftrace ring buffer is per CPU, this size is the size of each per CPU ring buffer inside the kernel. Using "-b 10000" on a machine with 4 CPUs will make Ftrace have a total buffer size of 40 Megs. -k By default, when trace-cmd is finished tracing, it will reset the buffers and disable all the tracing that it enabled. This option keeps trace-cmd from disabling the tracer and reseting the buffer. This option is useful for debugging trace-cmd. Note: usually trace-cmd will set the "tracing_on" file back to what it was before it was called. This option will leave that file set to zero. -i By default, if an event is listed that trace-cmd does not find, it will exit with an error. This option will just ignore events that are listed on the command line but are not found on the system. -N host:port If another machine is running "trace-cmd listen", this option is used to have the data sent to that machine with UDP packets. Instead of writing to an output file, the data is sent off to a remote box. This is ideal for embedded machines with little storage, or having a single machine that will keep all the data in a single repository. Note: This option is not supported with latency tracer plugins: wakeup, wakeup_rt, irqsoff, preemptoff and preemptirqsoff -t This option is used with -N, when there's a need to send the live data with TCP packets instead of UDP. Although TCP is not nearly as fast as sending the UDP packets, but it may be needed if the network is not that reliable, the amount of data is not that intensive, and a guarantee is needed that all traced information is transfered successfully. --date With the --date option, "trace-cmd" will write timestamps into the trace buffer after it has finished recording. It will then map the timestamp to gettimeofday which will allow wall time output from the timestamps reading the created trace.dat file. EXAMPLES
The basic way to trace all events: # trace-cmd record -e all ls > /dev/null # trace-cmd report trace-cmd-13541 [003] 106260.693809: filemap_fault: address=0x128122 offset=0xce trace-cmd-13543 [001] 106260.693809: kmalloc: call_site=81128dd4 ptr=0xffff88003dd83800 bytes_req=768 bytes_alloc=1024 gfp_flags=GFP_KERNEL|GFP_ZERO ls-13545 [002] 106260.693809: kfree: call_site=810a7abb ptr=0x0 ls-13545 [002] 106260.693818: sys_exit_write: 0x1 To use the function tracer with sched switch tracing: # trace-cmd record -p function -e sched_switch ls > /dev/null # trace-cmd report ls-13587 [002] 106467.860310: function: hrtick_start_fair <-- pick_next_task_fair ls-13587 [002] 106467.860313: sched_switch: prev_comm=trace-cmd prev_pid=13587 prev_prio=120 prev_state=R ==> next_comm=trace-cmd next_pid=13583 next_prio=120 trace-cmd-13585 [001] 106467.860314: function: native_set_pte_at <-- __do_fault trace-cmd-13586 [003] 106467.860314: function: up_read <-- do_page_fault ls-13587 [002] 106467.860317: function: __phys_addr <-- schedule trace-cmd-13585 [001] 106467.860318: function: _raw_spin_unlock <-- __do_fault ls-13587 [002] 106467.860320: function: native_load_sp0 <-- __switch_to trace-cmd-13586 [003] 106467.860322: function: down_read_trylock <-- do_page_fault Here is a nice way to find what interrupts have the highest latency: # trace-cmd record -p function_graph -e irq_handler_entry -l do_IRQ sleep 10 # trace-cmd report <idle>-0 [000] 157412.933969: funcgraph_entry: | do_IRQ() { <idle>-0 [000] 157412.933974: irq_handler_entry: irq=48 name=eth0 <idle>-0 [000] 157412.934004: funcgraph_exit: + 36.358 us | } <idle>-0 [000] 157413.895004: funcgraph_entry: | do_IRQ() { <idle>-0 [000] 157413.895011: irq_handler_entry: irq=48 name=eth0 <idle>-0 [000] 157413.895026: funcgraph_exit: + 24.014 us | } <idle>-0 [000] 157415.891762: funcgraph_entry: | do_IRQ() { <idle>-0 [000] 157415.891769: irq_handler_entry: irq=48 name=eth0 <idle>-0 [000] 157415.891784: funcgraph_exit: + 22.928 us | } <idle>-0 [000] 157415.934869: funcgraph_entry: | do_IRQ() { <idle>-0 [000] 157415.934874: irq_handler_entry: irq=48 name=eth0 <idle>-0 [000] 157415.934906: funcgraph_exit: + 37.512 us | } <idle>-0 [000] 157417.888373: funcgraph_entry: | do_IRQ() { <idle>-0 [000] 157417.888381: irq_handler_entry: irq=48 name=eth0 <idle>-0 [000] 157417.888398: funcgraph_exit: + 25.943 us | } SEE ALSO
trace-cmd(1), trace-cmd-report(1), trace-cmd-start(1), trace-cmd-stop(1), trace-cmd-extract(1), trace-cmd-reset(1), trace-cmd-split(1), trace-cmd-list(1), trace-cmd-listen(1) AUTHOR
Written by Steven Rostedt, <[1]> RESOURCES
git:// COPYING
Copyright (C) 2010 Red Hat, Inc. Free use of this software is granted under the terms of the GNU Public License (GPL). NOTES
1. 06/11/2014 TRACE-CMD-RECORD(1)
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