diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/DocBook/Makefile | 3 | ||||
| -rw-r--r-- | Documentation/DocBook/tracepoint.tmpl | 89 | ||||
| -rw-r--r-- | Documentation/trace/events.txt | 135 | ||||
| -rw-r--r-- | Documentation/trace/power.txt | 17 |
4 files changed, 243 insertions, 1 deletions
diff --git a/Documentation/DocBook/Makefile b/Documentation/DocBook/Makefile index b1eb661e6302..9632444f6c62 100644 --- a/Documentation/DocBook/Makefile +++ b/Documentation/DocBook/Makefile @@ -13,7 +13,8 @@ DOCBOOKS := z8530book.xml mcabook.xml device-drivers.xml \ gadget.xml libata.xml mtdnand.xml librs.xml rapidio.xml \ genericirq.xml s390-drivers.xml uio-howto.xml scsi.xml \ mac80211.xml debugobjects.xml sh.xml regulator.xml \ - alsa-driver-api.xml writing-an-alsa-driver.xml + alsa-driver-api.xml writing-an-alsa-driver.xml \ + tracepoint.xml ### # The build process is as follows (targets): diff --git a/Documentation/DocBook/tracepoint.tmpl b/Documentation/DocBook/tracepoint.tmpl new file mode 100644 index 000000000000..b0756d0fd579 --- /dev/null +++ b/Documentation/DocBook/tracepoint.tmpl @@ -0,0 +1,89 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" + "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> + +<book id="Tracepoints"> + <bookinfo> + <title>The Linux Kernel Tracepoint API</title> + + <authorgroup> + <author> + <firstname>Jason</firstname> + <surname>Baron</surname> + <affiliation> + <address> + <email>jbaron@redhat.com</email> + </address> + </affiliation> + </author> + </authorgroup> + + <legalnotice> + <para> + This documentation is free software; you can redistribute + it and/or modify it under the terms of the GNU General Public + License as published by the Free Software Foundation; either + version 2 of the License, or (at your option) any later + version. + </para> + + <para> + This program is distributed in the hope that it will be + useful, but WITHOUT ANY WARRANTY; without even the implied + warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. + See the GNU General Public License for more details. + </para> + + <para> + You should have received a copy of the GNU General Public + License along with this program; if not, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, + MA 02111-1307 USA + </para> + + <para> + For more details see the file COPYING in the source + distribution of Linux. + </para> + </legalnotice> + </bookinfo> + + <toc></toc> + <chapter id="intro"> + <title>Introduction</title> + <para> + Tracepoints are static probe points that are located in strategic points + throughout the kernel. 'Probes' register/unregister with tracepoints + via a callback mechanism. The 'probes' are strictly typed functions that + are passed a unique set of parameters defined by each tracepoint. + </para> + + <para> + From this simple callback mechanism, 'probes' can be used to profile, debug, + and understand kernel behavior. There are a number of tools that provide a + framework for using 'probes'. These tools include Systemtap, ftrace, and + LTTng. + </para> + + <para> + Tracepoints are defined in a number of header files via various macros. Thus, + the purpose of this document is to provide a clear accounting of the available + tracepoints. The intention is to understand not only what tracepoints are + available but also to understand where future tracepoints might be added. + </para> + + <para> + The API presented has functions of the form: + <function>trace_tracepointname(function parameters)</function>. These are the + tracepoints callbacks that are found throughout the code. Registering and + unregistering probes with these callback sites is covered in the + <filename>Documentation/trace/*</filename> directory. + </para> + </chapter> + + <chapter id="irq"> + <title>IRQ</title> +!Iinclude/trace/events/irq.h + </chapter> + +</book> diff --git a/Documentation/trace/events.txt b/Documentation/trace/events.txt new file mode 100644 index 000000000000..abdee664c0f6 --- /dev/null +++ b/Documentation/trace/events.txt @@ -0,0 +1,135 @@ + Event Tracing + + Documentation written by Theodore Ts'o + +Introduction +============ + +Tracepoints (see Documentation/trace/tracepoints.txt) can be used +without creating custom kernel modules to register probe functions +using the event tracing infrastructure. + +Not all tracepoints can be traced using the event tracing system; +the kernel developer must provide code snippets which define how the +tracing information is saved into the tracing buffer, and how the +the tracing information should be printed. + +Using Event Tracing +=================== + +The events which are available for tracing can be found in the file +/sys/kernel/debug/tracing/available_events. + +To enable a particular event, such as 'sched_wakeup', simply echo it +to /sys/debug/tracing/set_event. For example: + + # echo sched_wakeup > /sys/kernel/debug/tracing/set_event + +[ Note: events can also be enabled/disabled via the 'enabled' toggle + found in the /sys/kernel/tracing/events/ hierarchy of directories. ] + +To disable an event, echo the event name to the set_event file prefixed +with an exclamation point: + + # echo '!sched_wakeup' >> /sys/kernel/debug/tracing/set_event + +To disable events, echo an empty line to the set_event file: + + # echo > /sys/kernel/debug/tracing/set_event + +The events are organized into subsystems, such as ext4, irq, sched, +etc., and a full event name looks like this: <subsystem>:<event>. The +subsystem name is optional, but it is displayed in the available_events +file. All of the events in a subsystem can be specified via the syntax +"<subsystem>:*"; for example, to enable all irq events, you can use the +command: + + # echo 'irq:*' > /sys/kernel/debug/tracing/set_event + +Defining an event-enabled tracepoint +------------------------------------ + +A kernel developer which wishes to define an event-enabled tracepoint +must declare the tracepoint using TRACE_EVENT instead of DECLARE_TRACE. +This is done via two header files in include/trace. For example, to +event-enable the jbd2 subsystem, we must create two files, +include/trace/jbd2.h and include/trace/jbd2_event_types.h. The +include/trace/jbd2.h file should be included by kernel source files that +will have a tracepoint inserted, and might look like this: + +#ifndef _TRACE_JBD2_H +#define _TRACE_JBD2_H + +#include <linux/jbd2.h> +#include <linux/tracepoint.h> + +#include <trace/jbd2_event_types.h> + +#endif + +In a file that utilizes a jbd2 tracepoint, this header file would be +included. Note that you still have to use DEFINE_TRACE(). So for +example, if fs/jbd2/commit.c planned to use the jbd2_start_commit +tracepoint, it would have the following near the beginning of the file: + +#include <trace/jbd2.h> + +DEFINE_TRACE(jbd2_start_commit); + +Then in the function that would call the tracepoint, it would call the +tracepoint function. (For more information, please see the tracepoint +documentation in Documentation/trace/tracepoints.txt): + + trace_jbd2_start_commit(journal, commit_transaction); + +The code snippets which allow jbd2_start_commit to be an event-enabled +tracepoint are placed in the file include/trace/jbd2_event_types.h: + +/* use <trace/jbd2.h> instead */ +#ifndef TRACE_EVENT +# error Do not include this file directly. +# error Unless you know what you are doing. +#endif + +#undef TRACE_SYSTEM +#define TRACE_SYSTEM jbd2 + +#include <linux/jbd2.h> + +TRACE_EVENT(jbd2_start_commit, + TP_PROTO(journal_t *journal, transaction_t *commit_transaction), + TP_ARGS(journal, commit_transaction), + TP_STRUCT__entry( + __array( char, devname, BDEVNAME_SIZE+24 ) + __field( int, transaction ) + ), + TP_fast_assign( + memcpy(__entry->devname, journal->j_devname, BDEVNAME_SIZE+24); + __entry->transaction = commit_transaction->t_tid; + ), + TP_printk("dev %s transaction %d", + __entry->devname, __entry->transaction) +); + +The TP_PROTO and TP_ARGS are unchanged from DECLARE_TRACE. The new +arguments to TRACE_EVENT are TP_STRUCT__entry, TP_fast_assign, and +TP_printk. + +TP_STRUCT__entry defines the data structure which will be stored in the +trace buffer. Normally, fields in __entry will be arrays or simple +types. It is possible to place data structures in __entry --- however, +pointers in the data structure can not be trusted, since they will be +accessed sometime later by TP_printk, and if the data structure contains +fields that will not or cannot be used by TP_printk, this will waste +space in the trace buffer. In general, data structures should be +avoided, unless they do only contain non-pointer types and all of the +fields will be used by TP_printk. + +TP_fast_assign defines the code snippet which saves information into the +__entry data structure, using the passed-in arguments defined in +TP_PROTO and TP_ARGS. + +Finally, TP_printk will print the __entry data structure. At the time +when the code snippet defined by TP_printk is executed, it will not have +access to the TP_ARGS arguments; it can only use the information saved +in the __entry data structure. diff --git a/Documentation/trace/power.txt b/Documentation/trace/power.txt new file mode 100644 index 000000000000..cd805e16dc27 --- /dev/null +++ b/Documentation/trace/power.txt @@ -0,0 +1,17 @@ +The power tracer collects detailed information about C-state and P-state +transitions, instead of just looking at the high-level "average" +information. + +There is a helper script found in scrips/tracing/power.pl in the kernel +sources which can be used to parse this information and create a +Scalable Vector Graphics (SVG) picture from the trace data. + +To use this tracer: + + echo 0 > /sys/kernel/debug/tracing/tracing_enabled + echo power > /sys/kernel/debug/tracing/current_tracer + echo 1 > /sys/kernel/debug/tracing/tracing_enabled + sleep 1 + echo 0 > /sys/kernel/debug/tracing/tracing_enabled + cat /sys/kernel/debug/tracing/trace | \ + perl scripts/tracing/power.pl > out.sv |
