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tracing: Remove mentioning of legacy latency_trace file from documentation
The latency_trace file got removed a while back by commit
886b5b73d7 and has been replaced
by the latency-format option.
This patch fixes the documentation by reflecting this change.
Changes since v1:
- mention that the trace format is configurable through the
latency-format option
- Fix a couple mistakes related to the timestamps
Signed-off-by: Albin Tonnerre <albin.tonnerre@free-electrons.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <20090831204007.GE4237@pc-ras4041.res.insa>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
This commit is contained in:
Albin Tonnerre
Frederic Weisbecker
parent
c58b43218c
commit
4a88d44ab1
@ -85,26 +85,19 @@ of ftrace. Here is a list of some of the key files:
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This file holds the output of the trace in a human
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readable format (described below).
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latency_trace:
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This file shows the same trace but the information
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is organized more to display possible latencies
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in the system (described below).
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trace_pipe:
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The output is the same as the "trace" file but this
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file is meant to be streamed with live tracing.
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Reads from this file will block until new data
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is retrieved. Unlike the "trace" and "latency_trace"
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files, this file is a consumer. This means reading
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from this file causes sequential reads to display
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more current data. Once data is read from this
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file, it is consumed, and will not be read
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again with a sequential read. The "trace" and
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"latency_trace" files are static, and if the
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tracer is not adding more data, they will display
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the same information every time they are read.
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Reads from this file will block until new data is
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retrieved. Unlike the "trace" file, this file is a
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consumer. This means reading from this file causes
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sequential reads to display more current data. Once
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data is read from this file, it is consumed, and
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will not be read again with a sequential read. The
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"trace" file is static, and if the tracer is not
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adding more data,they will display the same
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information every time they are read.
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trace_options:
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@ -117,10 +110,10 @@ of ftrace. Here is a list of some of the key files:
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Some of the tracers record the max latency.
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For example, the time interrupts are disabled.
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This time is saved in this file. The max trace
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will also be stored, and displayed by either
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"trace" or "latency_trace". A new max trace will
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only be recorded if the latency is greater than
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the value in this file. (in microseconds)
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will also be stored, and displayed by "trace".
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A new max trace will only be recorded if the
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latency is greater than the value in this
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file. (in microseconds)
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buffer_size_kb:
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@ -210,7 +203,7 @@ Here is the list of current tracers that may be configured.
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the trace with the longest max latency.
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See tracing_max_latency. When a new max is recorded,
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it replaces the old trace. It is best to view this
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trace via the latency_trace file.
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trace with the latency-format option enabled.
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"preemptoff"
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@ -307,8 +300,8 @@ the lowest priority thread (pid 0).
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Latency trace format
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--------------------
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For traces that display latency times, the latency_trace file
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gives somewhat more information to see why a latency happened.
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When the latency-format option is enabled, the trace file gives
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somewhat more information to see why a latency happened.
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Here is a typical trace.
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# tracer: irqsoff
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@ -380,9 +373,10 @@ explains which is which.
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The above is mostly meaningful for kernel developers.
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time: This differs from the trace file output. The trace file output
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includes an absolute timestamp. The timestamp used by the
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latency_trace file is relative to the start of the trace.
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time: When the latency-format option is enabled, the trace file
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output includes a timestamp relative to the start of the
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trace. This differs from the output when latency-format
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is disabled, which includes an absolute timestamp.
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delay: This is just to help catch your eye a bit better. And
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needs to be fixed to be only relative to the same CPU.
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@ -440,7 +434,8 @@ Here are the available options:
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sym-addr:
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bash-4000 [01] 1477.606694: simple_strtoul <c0339346>
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verbose - This deals with the latency_trace file.
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verbose - This deals with the trace file when the
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latency-format option is enabled.
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bash 4000 1 0 00000000 00010a95 [58127d26] 1720.415ms \
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(+0.000ms): simple_strtoul (strict_strtoul)
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@ -472,7 +467,7 @@ Here are the available options:
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the app is no longer running
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The lookup is performed when you read
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trace,trace_pipe,latency_trace. Example:
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trace,trace_pipe. Example:
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a.out-1623 [000] 40874.465068: /root/a.out[+0x480] <-/root/a.out[+0
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x494] <- /root/a.out[+0x4a8] <- /lib/libc-2.7.so[+0x1e1a6]
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@ -481,6 +476,11 @@ x494] <- /root/a.out[+0x4a8] <- /lib/libc-2.7.so[+0x1e1a6]
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every scheduling event. Will add overhead if
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there's a lot of tasks running at once.
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latency-format - This option changes the trace. When
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it is enabled, the trace displays
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additional information about the
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latencies, as described in "Latency
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trace format".
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sched_switch
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------------
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@ -596,12 +596,13 @@ To reset the maximum, echo 0 into tracing_max_latency. Here is
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an example:
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# echo irqsoff > current_tracer
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# echo latency-format > trace_options
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# echo 0 > tracing_max_latency
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# echo 1 > tracing_enabled
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# ls -ltr
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[...]
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# echo 0 > tracing_enabled
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# cat latency_trace
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# cat trace
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# tracer: irqsoff
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#
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irqsoff latency trace v1.1.5 on 2.6.26
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@ -703,12 +704,13 @@ which preemption was disabled. The control of preemptoff tracer
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is much like the irqsoff tracer.
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# echo preemptoff > current_tracer
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# echo latency-format > trace_options
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# echo 0 > tracing_max_latency
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# echo 1 > tracing_enabled
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# ls -ltr
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[...]
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# echo 0 > tracing_enabled
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# cat latency_trace
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# cat trace
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# tracer: preemptoff
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#
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preemptoff latency trace v1.1.5 on 2.6.26-rc8
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@ -850,12 +852,13 @@ Again, using this trace is much like the irqsoff and preemptoff
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tracers.
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# echo preemptirqsoff > current_tracer
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# echo latency-format > trace_options
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# echo 0 > tracing_max_latency
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# echo 1 > tracing_enabled
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# ls -ltr
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[...]
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# echo 0 > tracing_enabled
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# cat latency_trace
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# cat trace
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# tracer: preemptirqsoff
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#
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preemptirqsoff latency trace v1.1.5 on 2.6.26-rc8
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@ -1012,11 +1015,12 @@ Instead of performing an 'ls', we will run 'sleep 1' under
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'chrt' which changes the priority of the task.
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# echo wakeup > current_tracer
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# echo latency-format > trace_options
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# echo 0 > tracing_max_latency
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# echo 1 > tracing_enabled
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# chrt -f 5 sleep 1
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# echo 0 > tracing_enabled
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# cat latency_trace
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# cat trace
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# tracer: wakeup
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#
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wakeup latency trace v1.1.5 on 2.6.26-rc8
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