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diff --git a/Documentation/trace/boottime-trace.rst b/Documentation/trace/boottime-trace.rst new file mode 100644 index 000000000000..d594597201fd --- /dev/null +++ b/Documentation/trace/boottime-trace.rst @@ -0,0 +1,301 @@ +.. SPDX-License-Identifier: GPL-2.0 + +================= +Boot-time tracing +================= + +:Author: Masami Hiramatsu <mhiramat@kernel.org> + +Overview +======== + +Boot-time tracing allows users to trace boot-time process including +device initialization with full features of ftrace including per-event +filter and actions, histograms, kprobe-events and synthetic-events, +and trace instances. +Since kernel command line is not enough to control these complex features, +this uses bootconfig file to describe tracing feature programming. + +Options in the Boot Config +========================== + +Here is the list of available options list for boot time tracing in +boot config file [1]_. All options are under "ftrace." or "kernel." +prefix. See kernel parameters for the options which starts +with "kernel." prefix [2]_. + +.. [1] See :ref:`Documentation/admin-guide/bootconfig.rst <bootconfig>` +.. [2] See :ref:`Documentation/admin-guide/kernel-parameters.rst <kernelparameters>` + +Ftrace Global Options +--------------------- + +Ftrace global options have "kernel." prefix in boot config, which means +these options are passed as a part of kernel legacy command line. + +kernel.tp_printk + Output trace-event data on printk buffer too. + +kernel.dump_on_oops [= MODE] + Dump ftrace on Oops. If MODE = 1 or omitted, dump trace buffer + on all CPUs. If MODE = 2, dump a buffer on a CPU which kicks Oops. + +kernel.traceoff_on_warning + Stop tracing if WARN_ON() occurs. + +kernel.fgraph_max_depth = MAX_DEPTH + Set MAX_DEPTH to maximum depth of fgraph tracer. + +kernel.fgraph_filters = FILTER[, FILTER2...] + Add fgraph tracing function filters. + +kernel.fgraph_notraces = FILTER[, FILTER2...] + Add fgraph non-tracing function filters. + + +Ftrace Per-instance Options +--------------------------- + +These options can be used for each instance including global ftrace node. + +ftrace.[instance.INSTANCE.]options = OPT1[, OPT2[...]] + Enable given ftrace options. + +ftrace.[instance.INSTANCE.]tracing_on = 0|1 + Enable/Disable tracing on this instance when starting boot-time tracing. + (you can enable it by the "traceon" event trigger action) + +ftrace.[instance.INSTANCE.]trace_clock = CLOCK + Set given CLOCK to ftrace's trace_clock. + +ftrace.[instance.INSTANCE.]buffer_size = SIZE + Configure ftrace buffer size to SIZE. You can use "KB" or "MB" + for that SIZE. + +ftrace.[instance.INSTANCE.]alloc_snapshot + Allocate snapshot buffer. + +ftrace.[instance.INSTANCE.]cpumask = CPUMASK + Set CPUMASK as trace cpu-mask. + +ftrace.[instance.INSTANCE.]events = EVENT[, EVENT2[...]] + Enable given events on boot. You can use a wild card in EVENT. + +ftrace.[instance.INSTANCE.]tracer = TRACER + Set TRACER to current tracer on boot. (e.g. function) + +ftrace.[instance.INSTANCE.]ftrace.filters + This will take an array of tracing function filter rules. + +ftrace.[instance.INSTANCE.]ftrace.notraces + This will take an array of NON-tracing function filter rules. + + +Ftrace Per-Event Options +------------------------ + +These options are setting per-event options. + +ftrace.[instance.INSTANCE.]event.GROUP.EVENT.enable + Enable GROUP:EVENT tracing. + +ftrace.[instance.INSTANCE.]event.GROUP.enable + Enable all event tracing within GROUP. + +ftrace.[instance.INSTANCE.]event.enable + Enable all event tracing. + +ftrace.[instance.INSTANCE.]event.GROUP.EVENT.filter = FILTER + Set FILTER rule to the GROUP:EVENT. + +ftrace.[instance.INSTANCE.]event.GROUP.EVENT.actions = ACTION[, ACTION2[...]] + Set ACTIONs to the GROUP:EVENT. + +ftrace.[instance.INSTANCE.]event.kprobes.EVENT.probes = PROBE[, PROBE2[...]] + Defines new kprobe event based on PROBEs. It is able to define + multiple probes on one event, but those must have same type of + arguments. This option is available only for the event which + group name is "kprobes". + +ftrace.[instance.INSTANCE.]event.synthetic.EVENT.fields = FIELD[, FIELD2[...]] + Defines new synthetic event with FIELDs. Each field should be + "type varname". + +Note that kprobe and synthetic event definitions can be written under +instance node, but those are also visible from other instances. So please +take care for event name conflict. + +Ftrace Histogram Options +------------------------ + +Since it is too long to write a histogram action as a string for per-event +action option, there are tree-style options under per-event 'hist' subkey +for the histogram actions. For the detail of the each parameter, +please read the event histogram document (Documentation/trace/histogram.rst) + +ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]keys = KEY1[, KEY2[...]] + Set histogram key parameters. (Mandatory) + The 'N' is a digit string for the multiple histogram. You can omit it + if there is one histogram on the event. + +ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]values = VAL1[, VAL2[...]] + Set histogram value parameters. + +ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]sort = SORT1[, SORT2[...]] + Set histogram sort parameter options. + +ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]size = NR_ENTRIES + Set histogram size (number of entries). + +ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]name = NAME + Set histogram name. + +ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]var.VARIABLE = EXPR + Define a new VARIABLE by EXPR expression. + +ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]<pause|continue|clear> + Set histogram control parameter. You can set one of them. + +ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]onmatch.[M.]event = GROUP.EVENT + Set histogram 'onmatch' handler matching event parameter. + The 'M' is a digit string for the multiple 'onmatch' handler. You can omit it + if there is one 'onmatch' handler on this histogram. + +ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]onmatch.[M.]trace = EVENT[, ARG1[...]] + Set histogram 'trace' action for 'onmatch'. + EVENT must be a synthetic event name, and ARG1... are parameters + for that event. Mandatory if 'onmatch.event' option is set. + +ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]onmax.[M.]var = VAR + Set histogram 'onmax' handler variable parameter. + +ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]onchange.[M.]var = VAR + Set histogram 'onchange' handler variable parameter. + +ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]<onmax|onchange>.[M.]save = ARG1[, ARG2[...]] + Set histogram 'save' action parameters for 'onmax' or 'onchange' handler. + This option or below 'snapshot' option is mandatory if 'onmax.var' or + 'onchange.var' option is set. + +ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]<onmax|onchange>.[M.]snapshot + Set histogram 'snapshot' action for 'onmax' or 'onchange' handler. + This option or above 'save' option is mandatory if 'onmax.var' or + 'onchange.var' option is set. + +ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.filter = FILTER_EXPR + Set histogram filter expression. You don't need 'if' in the FILTER_EXPR. + +Note that this 'hist' option can conflict with the per-event 'actions' +option if the 'actions' option has a histogram action. + + +When to Start +============= + +All boot-time tracing options starting with ``ftrace`` will be enabled at the +end of core_initcall. This means you can trace the events from postcore_initcall. +Most of the subsystems and architecture dependent drivers will be initialized +after that (arch_initcall or subsys_initcall). Thus, you can trace those with +boot-time tracing. +If you want to trace events before core_initcall, you can use the options +starting with ``kernel``. Some of them will be enabled eariler than the initcall +processing (for example,. ``kernel.ftrace=function`` and ``kernel.trace_event`` +will start before the initcall.) + + +Examples +======== + +For example, to add filter and actions for each event, define kprobe +events, and synthetic events with histogram, write a boot config like +below:: + + ftrace.event { + task.task_newtask { + filter = "pid < 128" + enable + } + kprobes.vfs_read { + probes = "vfs_read $arg1 $arg2" + filter = "common_pid < 200" + enable + } + synthetic.initcall_latency { + fields = "unsigned long func", "u64 lat" + hist { + keys = func.sym, lat + values = lat + sort = lat + } + } + initcall.initcall_start.hist { + keys = func + var.ts0 = common_timestamp.usecs + } + initcall.initcall_finish.hist { + keys = func + var.lat = common_timestamp.usecs - $ts0 + onmatch { + event = initcall.initcall_start + trace = initcall_latency, func, $lat + } + } + } + +Also, boot-time tracing supports "instance" node, which allows us to run +several tracers for different purpose at once. For example, one tracer +is for tracing functions starting with "user\_", and others tracing +"kernel\_" functions, you can write boot config as below:: + + ftrace.instance { + foo { + tracer = "function" + ftrace.filters = "user_*" + } + bar { + tracer = "function" + ftrace.filters = "kernel_*" + } + } + +The instance node also accepts event nodes so that each instance +can customize its event tracing. + +With the trigger action and kprobes, you can trace function-graph while +a function is called. For example, this will trace all function calls in +the pci_proc_init():: + + ftrace { + tracing_on = 0 + tracer = function_graph + event.kprobes { + start_event { + probes = "pci_proc_init" + actions = "traceon" + } + end_event { + probes = "pci_proc_init%return" + actions = "traceoff" + } + } + } + + +This boot-time tracing also supports ftrace kernel parameters via boot +config. +For example, following kernel parameters:: + + trace_options=sym-addr trace_event=initcall:* tp_printk trace_buf_size=1M ftrace=function ftrace_filter="vfs*" + +This can be written in boot config like below:: + + kernel { + trace_options = sym-addr + trace_event = "initcall:*" + tp_printk + trace_buf_size = 1M + ftrace = function + ftrace_filter = "vfs*" + } + +Note that parameters start with "kernel" prefix instead of "ftrace". |