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-rw-r--r--Documentation/trace/ftrace.rst82
1 files changed, 66 insertions, 16 deletions
diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst
index ff658e27d25b..3b5614b1d1a5 100644
--- a/Documentation/trace/ftrace.rst
+++ b/Documentation/trace/ftrace.rst
@@ -125,10 +125,13 @@ of ftrace. Here is a list of some of the key files:
trace:
This file holds the output of the trace in a human
- readable format (described below). Note, tracing is temporarily
- disabled when the file is open for reading. Once all readers
- are closed, tracing is re-enabled. Opening this file for
+ readable format (described below). Opening this file for
writing with the O_TRUNC flag clears the ring buffer content.
+ Note, this file is not a consumer. If tracing is off
+ (no tracer running, or tracing_on is zero), it will produce
+ the same output each time it is read. When tracing is on,
+ it may produce inconsistent results as it tries to read
+ the entire buffer without consuming it.
trace_pipe:
@@ -142,9 +145,7 @@ of ftrace. Here is a list of some of the key files:
will not be read again with a sequential read. The
"trace" file is static, and if the tracer is not
adding more data, it will display the same
- information every time it is read. Unlike the
- "trace" file, opening this file for reading will not
- temporarily disable tracing.
+ information every time it is read.
trace_options:
@@ -262,6 +263,20 @@ of ftrace. Here is a list of some of the key files:
traced by the function tracer as well. This option will also
cause PIDs of tasks that exit to be removed from the file.
+ set_ftrace_notrace_pid:
+
+ Have the function tracer ignore threads whose PID are listed in
+ this file.
+
+ If the "function-fork" option is set, then when a task whose
+ PID is listed in this file forks, the child's PID will
+ automatically be added to this file, and the child will not be
+ traced by the function tracer as well. This option will also
+ cause PIDs of tasks that exit to be removed from the file.
+
+ If a PID is in both this file and "set_ftrace_pid", then this
+ file takes precedence, and the thread will not be traced.
+
set_event_pid:
Have the events only trace a task with a PID listed in this file.
@@ -273,6 +288,19 @@ of ftrace. Here is a list of some of the key files:
cause the PIDs of tasks to be removed from this file when the task
exits.
+ set_event_notrace_pid:
+
+ Have the events not trace a task with a PID listed in this file.
+ Note, sched_switch and sched_wakeup will trace threads not listed
+ in this file, even if a thread's PID is in the file if the
+ sched_switch or sched_wakeup events also trace a thread that should
+ be traced.
+
+ To have the PIDs of children of tasks with their PID in this file
+ added on fork, enable the "event-fork" option. That option will also
+ cause the PIDs of tasks to be removed from this file when the task
+ exits.
+
set_graph_function:
Functions listed in this file will cause the function graph
@@ -1125,6 +1153,12 @@ Here are the available options:
the trace displays additional information about the
latency, as described in "Latency trace format".
+ pause-on-trace
+ When set, opening the trace file for read, will pause
+ writing to the ring buffer (as if tracing_on was set to zero).
+ This simulates the original behavior of the trace file.
+ When the file is closed, tracing will be enabled again.
+
record-cmd
When any event or tracer is enabled, a hook is enabled
in the sched_switch trace point to fill comm cache
@@ -1176,6 +1210,8 @@ Here are the available options:
tasks fork. Also, when tasks with PIDs in set_event_pid exit,
their PIDs will be removed from the file.
+ This affects PIDs listed in set_event_notrace_pid as well.
+
function-trace
The latency tracers will enable function tracing
if this option is enabled (default it is). When
@@ -1190,6 +1226,8 @@ Here are the available options:
set_ftrace_pid exit, their PIDs will be removed from the
file.
+ This affects PIDs in set_ftrace_notrace_pid as well.
+
display-graph
When set, the latency tracers (irqsoff, wakeup, etc) will
use function graph tracing instead of function tracing.
@@ -2126,6 +2164,8 @@ periodically make a CPU constantly busy with interrupts disabled.
# cat trace
# tracer: hwlat
#
+ # entries-in-buffer/entries-written: 13/13 #P:8
+ #
# _-----=> irqs-off
# / _----=> need-resched
# | / _---=> hardirq/softirq
@@ -2133,12 +2173,18 @@ periodically make a CPU constantly busy with interrupts disabled.
# ||| / delay
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
# | | | |||| | |
- <...>-3638 [001] d... 19452.055471: #1 inner/outer(us): 12/14 ts:1499801089.066141940
- <...>-3638 [003] d... 19454.071354: #2 inner/outer(us): 11/9 ts:1499801091.082164365
- <...>-3638 [002] dn.. 19461.126852: #3 inner/outer(us): 12/9 ts:1499801098.138150062
- <...>-3638 [001] d... 19488.340960: #4 inner/outer(us): 8/12 ts:1499801125.354139633
- <...>-3638 [003] d... 19494.388553: #5 inner/outer(us): 8/12 ts:1499801131.402150961
- <...>-3638 [003] d... 19501.283419: #6 inner/outer(us): 0/12 ts:1499801138.297435289 nmi-total:4 nmi-count:1
+ <...>-1729 [001] d... 678.473449: #1 inner/outer(us): 11/12 ts:1581527483.343962693 count:6
+ <...>-1729 [004] d... 689.556542: #2 inner/outer(us): 16/9 ts:1581527494.889008092 count:1
+ <...>-1729 [005] d... 714.756290: #3 inner/outer(us): 16/16 ts:1581527519.678961629 count:5
+ <...>-1729 [001] d... 718.788247: #4 inner/outer(us): 9/17 ts:1581527523.889012713 count:1
+ <...>-1729 [002] d... 719.796341: #5 inner/outer(us): 13/9 ts:1581527524.912872606 count:1
+ <...>-1729 [006] d... 844.787091: #6 inner/outer(us): 9/12 ts:1581527649.889048502 count:2
+ <...>-1729 [003] d... 849.827033: #7 inner/outer(us): 18/9 ts:1581527654.889013793 count:1
+ <...>-1729 [007] d... 853.859002: #8 inner/outer(us): 9/12 ts:1581527658.889065736 count:1
+ <...>-1729 [001] d... 855.874978: #9 inner/outer(us): 9/11 ts:1581527660.861991877 count:1
+ <...>-1729 [001] d... 863.938932: #10 inner/outer(us): 9/11 ts:1581527668.970010500 count:1 nmi-total:7 nmi-count:1
+ <...>-1729 [007] d... 878.050780: #11 inner/outer(us): 9/12 ts:1581527683.385002600 count:1 nmi-total:5 nmi-count:1
+ <...>-1729 [007] d... 886.114702: #12 inner/outer(us): 9/12 ts:1581527691.385001600 count:1
The above output is somewhat the same in the header. All events will have
@@ -2148,7 +2194,7 @@ interrupts disabled 'd'. Under the FUNCTION title there is:
This is the count of events recorded that were greater than the
tracing_threshold (See below).
- inner/outer(us): 12/14
+ inner/outer(us): 11/11
This shows two numbers as "inner latency" and "outer latency". The test
runs in a loop checking a timestamp twice. The latency detected within
@@ -2156,11 +2202,15 @@ interrupts disabled 'd'. Under the FUNCTION title there is:
after the previous timestamp and the next timestamp in the loop is
the "outer latency".
- ts:1499801089.066141940
+ ts:1581527483.343962693
+
+ The absolute timestamp that the first latency was recorded in the window.
+
+ count:6
- The absolute timestamp that the event happened.
+ The number of times a latency was detected during the window.
- nmi-total:4 nmi-count:1
+ nmi-total:7 nmi-count:1
On architectures that support it, if an NMI comes in during the
test, the time spent in NMI is reported in "nmi-total" (in