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Merge branch 'tracing-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
* 'tracing-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: ring-buffer: prevent infinite looping on time stamping ftrace: disable tracing on resize ftrace: fix breakage in bin_fmt results ftrace: ftrace.txt version update ftrace: update txt document
This commit is contained in:
Linus Torvalds
commit
09eb3b5b1b
@ -8,7 +8,7 @@ Copyright 2008 Red Hat Inc.
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Reviewers: Elias Oltmanns, Randy Dunlap, Andrew Morton,
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John Kacur, and David Teigland.
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Written for: 2.6.27-rc1
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Written for: 2.6.28-rc2
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Introduction
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------------
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@ -50,26 +50,26 @@ of ftrace. Here is a list of some of the key files:
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Note: all time values are in microseconds.
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current_tracer : This is used to set or display the current tracer
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current_tracer: This is used to set or display the current tracer
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that is configured.
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available_tracers : This holds the different types of tracers that
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available_tracers: This holds the different types of tracers that
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have been compiled into the kernel. The tracers
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listed here can be configured by echoing their name
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into current_tracer.
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tracing_enabled : This sets or displays whether the current_tracer
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tracing_enabled: This sets or displays whether the current_tracer
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is activated and tracing or not. Echo 0 into this
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file to disable the tracer or 1 to enable it.
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trace : This file holds the output of the trace in a human readable
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trace: This file holds the output of the trace in a human readable
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format (described below).
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latency_trace : This file shows the same trace but the information
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latency_trace: 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 : The output is the same as the "trace" file but this
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trace_pipe: 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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@ -82,11 +82,11 @@ of ftrace. Here is a list of some of the key files:
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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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iter_ctrl : This file lets the user control the amount of data
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iter_ctrl: This file lets the user control the amount of data
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that is displayed in one of the above output
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files.
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trace_max_latency : Some of the tracers record the max latency.
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trace_max_latency: 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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@ -94,29 +94,26 @@ of ftrace. Here is a list of some of the key files:
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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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trace_entries : This sets or displays the number of trace
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entries each CPU buffer can hold. The tracer buffers
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are the same size for each CPU. The displayed number
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is the size of the CPU buffer and not total size. The
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trace_entries: This sets or displays the number of bytes each CPU
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buffer can hold. The tracer buffers are the same size
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for each CPU. The displayed number is the size of the
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CPU buffer and not total size of all buffers. The
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trace buffers are allocated in pages (blocks of memory
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that the kernel uses for allocation, usually 4 KB in size).
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Since each entry is smaller than a page, if the last
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allocated page has room for more entries than were
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requested, the rest of the page is used to allocate
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entries.
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If the last page allocated has room for more bytes
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than requested, the rest of the page will be used,
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making the actual allocation bigger than requested.
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(Note, the size may not be a multiple of the page size due
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to buffer managment overhead.)
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This can only be updated when the current_tracer
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is set to "none".
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is set to "nop".
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NOTE: It is planned on changing the allocated buffers
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from being the number of possible CPUS to
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the number of online CPUS.
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tracing_cpumask : This is a mask that lets the user only trace
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tracing_cpumask: This is a mask that lets the user only trace
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on specified CPUS. The format is a hex string
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representing the CPUS.
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set_ftrace_filter : When dynamic ftrace is configured in (see the
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set_ftrace_filter: When dynamic ftrace is configured in (see the
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section below "dynamic ftrace"), the code is dynamically
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modified (code text rewrite) to disable calling of the
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function profiler (mcount). This lets tracing be configured
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@ -130,14 +127,11 @@ of ftrace. Here is a list of some of the key files:
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be traced. If a function exists in both set_ftrace_filter
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and set_ftrace_notrace, the function will _not_ be traced.
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available_filter_functions : When a function is encountered the first
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time by the dynamic tracer, it is recorded and
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later the call is converted into a nop. This file
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lists the functions that have been recorded
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by the dynamic tracer and these functions can
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be used to set the ftrace filter by the above
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"set_ftrace_filter" file. (See the section "dynamic ftrace"
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below for more details).
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available_filter_functions: This lists the functions that ftrace
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has processed and can trace. These are the function
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names that you can pass to "set_ftrace_filter" or
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"set_ftrace_notrace". (See the section "dynamic ftrace"
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below for more details.)
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The Tracers
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@ -145,7 +139,7 @@ The Tracers
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Here is the list of current tracers that may be configured.
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ftrace - function tracer that uses mcount to trace all functions.
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function - function tracer that uses mcount to trace all functions.
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sched_switch - traces the context switches between tasks.
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@ -166,8 +160,8 @@ Here is the list of current tracers that may be configured.
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the highest priority task to get scheduled after
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it has been woken up.
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none - This is not a tracer. To remove all tracers from tracing
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simply echo "none" into current_tracer.
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nop - This is not a tracer. To remove all tracers from tracing
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simply echo "nop" into current_tracer.
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Examples of using the tracer
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@ -182,7 +176,7 @@ Output format:
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Here is an example of the output format of the file "trace"
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--------
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# tracer: ftrace
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# tracer: function
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#
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# TASK-PID CPU# TIMESTAMP FUNCTION
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# | | | | |
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@ -192,7 +186,7 @@ Here is an example of the output format of the file "trace"
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--------
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A header is printed with the tracer name that is represented by the trace.
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In this case the tracer is "ftrace". Then a header showing the format. Task
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In this case the tracer is "function". Then a header showing the format. Task
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name "bash", the task PID "4251", the CPU that it was running on
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"01", the timestamp in <secs>.<usecs> format, the function name that was
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traced "path_put" and the parent function that called this function
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@ -1003,22 +997,20 @@ is the stack for the hard interrupt. This hides the fact that NEED_RESCHED
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has been set. We do not see the 'N' until we switch back to the task's
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assigned stack.
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ftrace
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------
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function
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--------
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ftrace is not only the name of the tracing infrastructure, but it
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is also a name of one of the tracers. The tracer is the function
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tracer. Enabling the function tracer can be done from the
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debug file system. Make sure the ftrace_enabled is set otherwise
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this tracer is a nop.
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This tracer is the function tracer. Enabling the function tracer
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can be done from the debug file system. Make sure the ftrace_enabled is
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set; otherwise this tracer is a nop.
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# sysctl kernel.ftrace_enabled=1
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# echo ftrace > /debug/tracing/current_tracer
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# echo function > /debug/tracing/current_tracer
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# echo 1 > /debug/tracing/tracing_enabled
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# usleep 1
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# echo 0 > /debug/tracing/tracing_enabled
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# cat /debug/tracing/trace
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# tracer: ftrace
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# tracer: function
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#
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# TASK-PID CPU# TIMESTAMP FUNCTION
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# | | | | |
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@ -1040,10 +1032,10 @@ this tracer is a nop.
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[...]
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Note: ftrace uses ring buffers to store the above entries. The newest data
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may overwrite the oldest data. Sometimes using echo to stop the trace
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is not sufficient because the tracing could have overwritten the data
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that you wanted to record. For this reason, it is sometimes better to
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Note: function tracer uses ring buffers to store the above entries.
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The newest data may overwrite the oldest data. Sometimes using echo to
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stop the trace is not sufficient because the tracing could have overwritten
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the data that you wanted to record. For this reason, it is sometimes better to
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disable tracing directly from a program. This allows you to stop the
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tracing at the point that you hit the part that you are interested in.
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To disable the tracing directly from a C program, something like following
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@ -1077,18 +1069,31 @@ every kernel function, produced by the -pg switch in gcc), starts
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of pointing to a simple return. (Enabling FTRACE will include the
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-pg switch in the compiling of the kernel.)
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When dynamic ftrace is initialized, it calls kstop_machine to make
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the machine act like a uniprocessor so that it can freely modify code
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without worrying about other processors executing that same code. At
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initialization, the mcount calls are changed to call a "record_ip"
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function. After this, the first time a kernel function is called,
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it has the calling address saved in a hash table.
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At compile time every C file object is run through the
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recordmcount.pl script (located in the scripts directory). This
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script will process the C object using objdump to find all the
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locations in the .text section that call mcount. (Note, only
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the .text section is processed, since processing other sections
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like .init.text may cause races due to those sections being freed).
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Later on the ftraced kernel thread is awoken and will again call
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kstop_machine if new functions have been recorded. The ftraced thread
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will change all calls to mcount to "nop". Just calling mcount
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and having mcount return has shown a 10% overhead. By converting
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it to a nop, there is no measurable overhead to the system.
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A new section called "__mcount_loc" is created that holds references
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to all the mcount call sites in the .text section. This section is
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compiled back into the original object. The final linker will add
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all these references into a single table.
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On boot up, before SMP is initialized, the dynamic ftrace code
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scans this table and updates all the locations into nops. It also
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records the locations, which are added to the available_filter_functions
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list. Modules are processed as they are loaded and before they are
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executed. When a module is unloaded, it also removes its functions from
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the ftrace function list. This is automatic in the module unload
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code, and the module author does not need to worry about it.
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When tracing is enabled, kstop_machine is called to prevent races
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with the CPUS executing code being modified (which can cause the
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CPU to do undesireable things), and the nops are patched back
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to calls. But this time, they do not call mcount (which is just
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a function stub). They now call into the ftrace infrastructure.
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One special side-effect to the recording of the functions being
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traced is that we can now selectively choose which functions we
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@ -1251,36 +1256,6 @@ Produces:
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We can see that there's no more lock or preempt tracing.
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ftraced
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-------
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As mentioned above, when dynamic ftrace is configured in, a kernel
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thread wakes up once a second and checks to see if there are mcount
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calls that need to be converted into nops. If there are not any, then
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it simply goes back to sleep. But if there are some, it will call
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kstop_machine to convert the calls to nops.
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There may be a case in which you do not want this added latency.
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Perhaps you are doing some audio recording and this activity might
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cause skips in the playback. There is an interface to disable
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and enable the "ftraced" kernel thread.
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# echo 0 > /debug/tracing/ftraced_enabled
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This will disable the calling of kstop_machine to update the
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mcount calls to nops. Remember that there is a large overhead
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to calling mcount. Without this kernel thread, that overhead will
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exist.
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If there are recorded calls to mcount, any write to the ftraced_enabled
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file will cause the kstop_machine to run. This means that a
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user can manually perform the updates when they want to by simply
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echoing a '0' into the ftraced_enabled file.
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The updates are also done at the beginning of enabling a tracer
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that uses ftrace function recording.
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trace_pipe
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----------
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@ -1289,14 +1264,14 @@ on the tracing is different. Every read from trace_pipe is consumed.
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This means that subsequent reads will be different. The trace
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is live.
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# echo ftrace > /debug/tracing/current_tracer
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# echo function > /debug/tracing/current_tracer
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# cat /debug/tracing/trace_pipe > /tmp/trace.out &
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[1] 4153
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# echo 1 > /debug/tracing/tracing_enabled
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# usleep 1
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# echo 0 > /debug/tracing/tracing_enabled
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# cat /debug/tracing/trace
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# tracer: ftrace
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# tracer: function
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#
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# TASK-PID CPU# TIMESTAMP FUNCTION
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# | | | | |
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@ -1317,7 +1292,7 @@ is live.
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Note, reading the trace_pipe file will block until more input is added.
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By changing the tracer, trace_pipe will issue an EOF. We needed
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to set the ftrace tracer _before_ cating the trace_pipe file.
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to set the function tracer _before_ we "cat" the trace_pipe file.
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trace entries
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@ -1334,10 +1309,10 @@ number of entries.
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65620
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Note, to modify this, you must have tracing completely disabled. To do that,
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echo "none" into the current_tracer. If the current_tracer is not set
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to "none", an EINVAL error will be returned.
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echo "nop" into the current_tracer. If the current_tracer is not set
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to "nop", an EINVAL error will be returned.
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# echo none > /debug/tracing/current_tracer
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# echo nop > /debug/tracing/current_tracer
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# echo 100000 > /debug/tracing/trace_entries
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# cat /debug/tracing/trace_entries
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100045
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@ -1060,7 +1060,7 @@ rb_reserve_next_event(struct ring_buffer_per_cpu *cpu_buffer,
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/* Did the write stamp get updated already? */
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if (unlikely(ts < cpu_buffer->write_stamp))
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goto again;
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delta = 0;
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if (test_time_stamp(delta)) {
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@ -1755,7 +1755,7 @@ static enum print_line_t print_bin_fmt(struct trace_iterator *iter)
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return TRACE_TYPE_HANDLED;
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SEQ_PUT_FIELD_RET(s, entry->pid);
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SEQ_PUT_FIELD_RET(s, iter->cpu);
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SEQ_PUT_FIELD_RET(s, entry->cpu);
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SEQ_PUT_FIELD_RET(s, iter->ts);
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switch (entry->type) {
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@ -2676,7 +2676,7 @@ tracing_entries_write(struct file *filp, const char __user *ubuf,
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{
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unsigned long val;
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char buf[64];
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int ret;
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int ret, cpu;
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struct trace_array *tr = filp->private_data;
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if (cnt >= sizeof(buf))
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@ -2704,6 +2704,14 @@ tracing_entries_write(struct file *filp, const char __user *ubuf,
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goto out;
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}
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/* disable all cpu buffers */
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for_each_tracing_cpu(cpu) {
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if (global_trace.data[cpu])
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atomic_inc(&global_trace.data[cpu]->disabled);
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if (max_tr.data[cpu])
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atomic_inc(&max_tr.data[cpu]->disabled);
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}
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if (val != global_trace.entries) {
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ret = ring_buffer_resize(global_trace.buffer, val);
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if (ret < 0) {
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@ -2735,6 +2743,13 @@ tracing_entries_write(struct file *filp, const char __user *ubuf,
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if (tracing_disabled)
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cnt = -ENOMEM;
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out:
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for_each_tracing_cpu(cpu) {
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if (global_trace.data[cpu])
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atomic_dec(&global_trace.data[cpu]->disabled);
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if (max_tr.data[cpu])
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atomic_dec(&max_tr.data[cpu]->disabled);
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}
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max_tr.entries = global_trace.entries;
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mutex_unlock(&trace_types_lock);
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