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Diffstat (limited to 'Documentation/trace/ftrace.rst')
| -rw-r--r-- | Documentation/trace/ftrace.rst | 64 |
1 files changed, 52 insertions, 12 deletions
diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst index 5aba74872ba7..d1f313a5f4ad 100644 --- a/Documentation/trace/ftrace.rst +++ b/Documentation/trace/ftrace.rst @@ -30,7 +30,7 @@ disabled and enabled, as well as for preemption and from a time a task is woken to the task is actually scheduled in. One of the most common uses of ftrace is the event tracing. -Throughout the kernel is hundreds of static event points that +Throughout the kernel are hundreds of static event points that can be enabled via the tracefs file system to see what is going on in certain parts of the kernel. @@ -366,6 +366,14 @@ of ftrace. Here is a list of some of the key files: for each function. The displayed address is the patch-site address and can differ from /proc/kallsyms address. + syscall_user_buf_size: + + Some system call trace events will record the data from a user + space address that one of the parameters point to. The amount of + data per event is limited. This file holds the max number of bytes + that will be recorded into the ring buffer to hold this data. + The max value is currently 165. + dyn_ftrace_total_info: This file is for debugging purposes. The number of functions that @@ -383,7 +391,7 @@ of ftrace. Here is a list of some of the key files: not be listed in this count. If the callback registered to be traced by a function with - the "save regs" attribute (thus even more overhead), a 'R' + the "save regs" attribute (thus even more overhead), an 'R' will be displayed on the same line as the function that is returning registers. @@ -392,7 +400,7 @@ of ftrace. Here is a list of some of the key files: an 'I' will be displayed on the same line as the function that can be overridden. - If a non ftrace trampoline is attached (BPF) a 'D' will be displayed. + If a non-ftrace trampoline is attached (BPF) a 'D' will be displayed. Note, normal ftrace trampolines can also be attached, but only one "direct" trampoline can be attached to a given function at a time. @@ -402,7 +410,7 @@ of ftrace. Here is a list of some of the key files: If a function had either the "ip modify" or a "direct" call attached to it in the past, a 'M' will be shown. This flag is never cleared. It is - used to know if a function was every modified by the ftrace infrastructure, + used to know if a function was ever modified by the ftrace infrastructure, and can be used for debugging. If the architecture supports it, it will also show what callback @@ -418,7 +426,7 @@ of ftrace. Here is a list of some of the key files: This file contains all the functions that ever had a function callback to it via the ftrace infrastructure. It has the same format as - enabled_functions but shows all functions that have every been + enabled_functions but shows all functions that have ever been traced. To see any function that has every been modified by "ip modify" or a @@ -517,7 +525,7 @@ of ftrace. Here is a list of some of the key files: Whenever an event is recorded into the ring buffer, a "timestamp" is added. This stamp comes from a specified clock. By default, ftrace uses the "local" clock. This - clock is very fast and strictly per cpu, but on some + clock is very fast and strictly per CPU, but on some systems it may not be monotonic with respect to other CPUs. In other words, the local clocks may not be in sync with local clocks on other CPUs. @@ -810,6 +818,12 @@ Here is the list of current tracers that may be configured. to draw a graph of function calls similar to C code source. + Note that the function graph calculates the timings of when the + function starts and returns internally and for each instance. If + there are two instances that run function graph tracer and traces + the same functions, the length of the timings may be slightly off as + each read the timestamp separately and not at the same time. + "blk" The block tracer. The tracer used by the blktrace user @@ -862,7 +876,7 @@ Here is the list of current tracers that may be configured. "mmiotrace" - A special tracer that is used to trace binary module. + A special tracer that is used to trace binary modules. It will trace all the calls that a module makes to the hardware. Everything it writes and reads from the I/O as well. @@ -1031,14 +1045,15 @@ explains which is which. CPU#: The CPU which the process was running on. irqs-off: 'd' interrupts are disabled. '.' otherwise. - .. caution:: If the architecture does not support a way to - read the irq flags variable, an 'X' will always - be printed here. need-resched: + - 'B' all, TIF_NEED_RESCHED, PREEMPT_NEED_RESCHED and TIF_RESCHED_LAZY is set, - 'N' both TIF_NEED_RESCHED and PREEMPT_NEED_RESCHED is set, - 'n' only TIF_NEED_RESCHED is set, - 'p' only PREEMPT_NEED_RESCHED is set, + - 'L' both PREEMPT_NEED_RESCHED and TIF_RESCHED_LAZY is set, + - 'b' both TIF_NEED_RESCHED and TIF_RESCHED_LAZY is set, + - 'l' only TIF_RESCHED_LAZY is set - '.' otherwise. hardirq/softirq: @@ -1186,6 +1201,31 @@ Here are the available options: trace_printk Can disable trace_printk() from writing into the buffer. + trace_printk_dest + Set to have trace_printk() and similar internal tracing functions + write into this instance. Note, only one trace instance can have + this set. By setting this flag, it clears the trace_printk_dest flag + of the instance that had it set previously. By default, the top + level trace has this set, and will get it set again if another + instance has it set then clears it. + + This flag cannot be cleared by the top level instance, as it is the + default instance. The only way the top level instance has this flag + cleared, is by it being set in another instance. + + copy_trace_marker + If there are applications that hard code writing into the top level + trace_marker file (/sys/kernel/tracing/trace_marker or trace_marker_raw), + and the tooling would like it to go into an instance, this option can + be used. Create an instance and set this option, and then all writes + into the top level trace_marker file will also be redirected into this + instance. + + Note, by default this option is set for the top level instance. If it + is disabled, then writes to the trace_marker or trace_marker_raw files + will not be written into the top level file. If no instance has this + option set, then a write will error with the errno of ENODEV. + annotate It is sometimes confusing when the CPU buffers are full and one CPU buffer had a lot of events recently, thus @@ -3058,7 +3098,7 @@ Notice that we lost the sys_nanosleep. # cat set_ftrace_filter hrtimer_run_queues hrtimer_run_pending - hrtimer_init + hrtimer_setup hrtimer_cancel hrtimer_try_to_cancel hrtimer_forward @@ -3096,7 +3136,7 @@ Again, now we want to append. # cat set_ftrace_filter hrtimer_run_queues hrtimer_run_pending - hrtimer_init + hrtimer_setup hrtimer_cancel hrtimer_try_to_cancel hrtimer_forward |