From 56c49951747f250d8398582509e02ae5ce1d36d1 Mon Sep 17 00:00:00 2001 From: Theodore Ts'o Date: Sat, 11 Apr 2009 15:51:19 -0400 Subject: tracing: Add documentation for the power tracer Signed-off-by: "Theodore Ts'o" Acked-by: Arjan van de Ven Cc: Frederic Weisbecker Cc: Steven Rostedt LKML-Reference: <1239479479-2603-4-git-send-email-tytso@mit.edu> Signed-off-by: Ingo Molnar --- Documentation/trace/power.txt | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) create mode 100644 Documentation/trace/power.txt (limited to 'Documentation') diff --git a/Documentation/trace/power.txt b/Documentation/trace/power.txt new file mode 100644 index 00000000000..cd805e16dc2 --- /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 -- cgit v1.2.3 From abd41443ac76d3e9c29a8c1d9e9a3312306cc55e Mon Sep 17 00:00:00 2001 From: Theodore Ts'o Date: Sat, 11 Apr 2009 15:51:18 -0400 Subject: tracing: Document the event tracing system Signed-off-by: "Theodore Ts'o" Cc: Theodore Ts'o Cc: Steven Rostedt LKML-Reference: <1239479479-2603-3-git-send-email-tytso@mit.edu> Signed-off-by: Ingo Molnar --- Documentation/trace/events.txt | 135 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 135 insertions(+) create mode 100644 Documentation/trace/events.txt (limited to 'Documentation') diff --git a/Documentation/trace/events.txt b/Documentation/trace/events.txt new file mode 100644 index 00000000000..abdee664c0f --- /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: :. 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 +":*"; 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 +#include + +#include + +#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 + +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 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 + +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. -- cgit v1.2.3 From a76f8c6da1e48fd4ef025f42c736389532ff30ba Mon Sep 17 00:00:00 2001 From: Jason Baron Date: Thu, 30 Apr 2009 13:29:42 -0400 Subject: tracing: add new tracepoints docbook Add tracepoint docbook. This will help us document and understand what tracepoints are in the kernel. Since there are multiple macros, and files that contain tracepoints. [ Impact: add documentation ] Signed-off-by: Jason Baron Acked-by: Randy Dunlap Cc: akpm@linux-foundation.org Cc: rostedt@goodmis.org Cc: fweisbec@gmail.com Cc: mathieu.desnoyers@polymtl.ca Cc: wcohen@redhat.com LKML-Reference: <84160b6bd94aff02455da7e12bad054d34c579a0.1241107197.git.jbaron@redhat.com> Signed-off-by: Ingo Molnar --- Documentation/DocBook/Makefile | 3 +- Documentation/DocBook/tracepoint.tmpl | 84 +++++++++++++++++++++++++++++++++++ 2 files changed, 86 insertions(+), 1 deletion(-) create mode 100644 Documentation/DocBook/tracepoint.tmpl (limited to 'Documentation') diff --git a/Documentation/DocBook/Makefile b/Documentation/DocBook/Makefile index 8918a32c6b3..4c8f4d6e114 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 00000000000..70891bc6849 --- /dev/null +++ b/Documentation/DocBook/tracepoint.tmpl @@ -0,0 +1,84 @@ + + + + + + The Linux Kernel Tracepoint API + + + + Jason + Baron + +
+ jbaron@redhat.com +
+ + + + + + + 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. + + + + 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. + + + + 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 + + + + For more details see the file COPYING in the source + distribution of Linux. + + + + + + + Introduction + + 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. + + + + 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. + + + + 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. + + + + The API presented has functions of the form: + trace_tracepointname(function parameters). These are the + tracepoints callbacks that are found throughout the code. Registering and + unregistering probes with these callback sites is covered in the + Documentation/trace/* directory. + + + + -- cgit v1.2.3 From 9ee1983c9aa18f12388ef660d0c76a23dc112959 Mon Sep 17 00:00:00 2001 From: Jason Baron Date: Thu, 30 Apr 2009 13:29:47 -0400 Subject: tracing: add irq tracepoint documentation Document irqs for the newly created docbook. [ Impact: add documentation ] Signed-off-by: Jason Baron Acked-by: Randy Dunlap Cc: akpm@linux-foundation.org Cc: rostedt@goodmis.org Cc: fweisbec@gmail.com Cc: mathieu.desnoyers@polymtl.ca Cc: wcohen@redhat.com LKML-Reference: <73ff42be3420157667ec548e9b0e409c3cfad05f.1241107197.git.jbaron@redhat.com> Signed-off-by: Ingo Molnar --- Documentation/DocBook/tracepoint.tmpl | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'Documentation') diff --git a/Documentation/DocBook/tracepoint.tmpl b/Documentation/DocBook/tracepoint.tmpl index 70891bc6849..b0756d0fd57 100644 --- a/Documentation/DocBook/tracepoint.tmpl +++ b/Documentation/DocBook/tracepoint.tmpl @@ -81,4 +81,9 @@ + + IRQ +!Iinclude/trace/events/irq.h + + -- cgit v1.2.3 From 143c145e3a475065a4be661468d0df1bd0b25f74 Mon Sep 17 00:00:00 2001 From: Li Zefan Date: Tue, 19 May 2009 14:43:15 +0800 Subject: tracing/events: Documentation updates - fix some typos - document the difference between '>' and '>>' - document the 'enable' toggle - remove section "Defining an event-enabled tracepoint", since it's out-dated and sample/trace_events/ already serves this purpose. v2: add "Updated by Li Zefan" [ Impact: make documentation up-to-date ] Signed-off-by: Li Zefan Cc: Steven Rostedt Cc: Frederic Weisbecker Cc: "Theodore Ts'o" LKML-Reference: <4A125503.5060406@cn.fujitsu.com> Signed-off-by: Ingo Molnar --- Documentation/trace/events.txt | 159 +++++++++++++++-------------------------- 1 file changed, 57 insertions(+), 102 deletions(-) (limited to 'Documentation') diff --git a/Documentation/trace/events.txt b/Documentation/trace/events.txt index abdee664c0f..f157d7594ea 100644 --- a/Documentation/trace/events.txt +++ b/Documentation/trace/events.txt @@ -1,9 +1,10 @@ Event Tracing Documentation written by Theodore Ts'o + Updated by Li Zefan -Introduction -============ +1. Introduction +=============== Tracepoints (see Documentation/trace/tracepoints.txt) can be used without creating custom kernel modules to register probe functions @@ -12,30 +13,37 @@ 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. +tracing information should be printed. -Using Event Tracing -=================== +2. Using Event Tracing +====================== + +2.1 Via the 'set_event' interface +--------------------------------- The events which are available for tracing can be found in the file -/sys/kernel/debug/tracing/available_events. +/debug/tracing/available_events. To enable a particular event, such as 'sched_wakeup', simply echo it -to /sys/debug/tracing/set_event. For example: +to /debug/tracing/set_event. For example: - # echo sched_wakeup > /sys/kernel/debug/tracing/set_event + # echo sched_wakeup >> /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. ] +[ Note: '>>' is necessary, otherwise it will firstly disable + all the events. ] 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 + # echo '!sched_wakeup' >> /debug/tracing/set_event + +To disable all events, echo an empty line to the set_event file: + + # echo > /debug/tracing/set_event -To disable events, echo an empty line to the set_event file: +To enable all events, echo '*:*' or '*:' to the set_event file: - # echo > /sys/kernel/debug/tracing/set_event + # echo *:* > /debug/tracing/set_event The events are organized into subsystems, such as ext4, irq, sched, etc., and a full event name looks like this: :. The @@ -44,92 +52,39 @@ file. All of the events in a subsystem can be specified via the syntax ":*"; 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 -#include - -#include - -#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 - -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 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 - -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. + # echo 'irq:*' > /debug/tracing/set_event + +2.2 Via the 'enable' toggle +--------------------------- + +The events available are also listed in /debug/tracing/events/ hierarchy +of directories. + +To enable event 'sched_wakeup': + + # echo 1 > /debug/tracing/events/sched/sched_wakeup/enable + +To disable it: + + # echo 0 > /debug/tracing/events/sched/sched_wakeup/enable + +To enable all events in sched subsystem: + + # echo 1 > /debug/tracing/events/sched/enable + +To eanble all events: + + # echo 1 > /debug/tracing/events/enable + +When reading one of these enable files, there are four results: + + 0 - all events this file affects are disabled + 1 - all events this file affects are enabled + X - there is a mixture of events enabled and disabled + ? - this file does not affect any event + +3. Defining an event-enabled tracepoint +======================================= + +See The example provided in samples/trace_events + -- cgit v1.2.3 From 29fcefba8a2f0fea11e2b721fe174a1832801284 Mon Sep 17 00:00:00 2001 From: Pekka Enberg Date: Sun, 24 May 2009 11:13:17 +0300 Subject: kmemtrace: fix kernel parameter documentation The kmemtrace.enable kernel parameter no longer works. To enable kmemtrace at boot-time, you must pass "ftrace=kmemtrace" instead. [ Impact: remove obsolete kernel parameter documentation ] Cc: Eduard - Gabriel Munteanu Signed-off-by: Pekka Enberg LKML-Reference: Signed-off-by: Frederic Weisbecker --- Documentation/kernel-parameters.txt | 10 ---------- 1 file changed, 10 deletions(-) (limited to 'Documentation') diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index e87bdbfbcc7..9243dd84f4d 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -56,7 +56,6 @@ parameter is applicable: ISAPNP ISA PnP code is enabled. ISDN Appropriate ISDN support is enabled. JOY Appropriate joystick support is enabled. - KMEMTRACE kmemtrace is enabled. LIBATA Libata driver is enabled LP Printer support is enabled. LOOP Loopback device support is enabled. @@ -1054,15 +1053,6 @@ and is between 256 and 4096 characters. It is defined in the file use the HighMem zone if it exists, and the Normal zone if it does not. - kmemtrace.enable= [KNL,KMEMTRACE] Format: { yes | no } - Controls whether kmemtrace is enabled - at boot-time. - - kmemtrace.subbufs=n [KNL,KMEMTRACE] Overrides the number of - subbufs kmemtrace's relay channel has. Set this - higher than default (KMEMTRACE_N_SUBBUFS in code) if - you experience buffer overruns. - kgdboc= [HW] kgdb over consoles. Requires a tty driver that supports console polling. (only serial suported for now) -- cgit v1.2.3 From 2af15d6a44b871ad4c2a651302374cde8f335480 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Thu, 28 May 2009 13:37:24 -0400 Subject: ftrace: add kernel command line function filtering When using ftrace=function on the command line to trace functions on boot up, one can not filter out functions that are commonly called. This patch adds two new ftrace command line commands. ftrace_notrace=function-list ftrace_filter=function-list Where function-list is a comma separated list of functions to filter. The ftrace_notrace will make the functions listed not be included in the function tracing, and ftrace_filter will only trace the functions listed. These two act the same as the debugfs/tracing/set_ftrace_notrace and debugfs/tracing/set_ftrace_filter respectively. The simple glob expressions that are allowed by the filter files can also be used by the command line interface. ftrace_notrace=rcu*,*lock,*spin* Will not trace any function that starts with rcu, ends with lock, or has the word spin in it. Note, if the self tests are enabled, they may interfere with the filtering set by the command lines. Signed-off-by: Steven Rostedt --- Documentation/kernel-parameters.txt | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) (limited to 'Documentation') diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 9243dd84f4d..fcd3bfbe74e 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -751,12 +751,25 @@ and is between 256 and 4096 characters. It is defined in the file ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. ftrace=[tracer] - [ftrace] will set and start the specified tracer + [FTRACE] will set and start the specified tracer as early as possible in order to facilitate early boot debugging. ftrace_dump_on_oops - [ftrace] will dump the trace buffers on oops. + [FTRACE] will dump the trace buffers on oops. + + ftrace_filter=[function-list] + [FTRACE] Limit the functions traced by the function + tracer at boot up. function-list is a comma separated + list of functions. This list can be changed at run + time by the set_ftrace_filter file in the debugfs + tracing directory. + + ftrace_notrace=[function-list] + [FTRACE] Do not trace the functions specified in + function-list. This list can be changed at run time + by the set_ftrace_notrace file in the debugfs + tracing directory. gamecon.map[2|3]= [HW,JOY] Multisystem joystick and NES/SNES/PSX pad -- cgit v1.2.3 From bc5c6c043d8381676339fb3da59cc4cc5921d368 Mon Sep 17 00:00:00 2001 From: Mike Frysinger Date: Wed, 10 Jun 2009 04:48:41 -0400 Subject: ftrace/documentation: fix typo in function grapher name The function graph tracer is called just "function_graph" (no trailing "_tracer" needed). Signed-off-by: Mike Frysinger LKML-Reference: <1244623722-6325-1-git-send-email-vapier@gentoo.org> Signed-off-by: Steven Rostedt --- Documentation/trace/ftrace.txt | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'Documentation') diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt index fd9a3e69381..5ad2ded8aa6 100644 --- a/Documentation/trace/ftrace.txt +++ b/Documentation/trace/ftrace.txt @@ -179,7 +179,7 @@ Here is the list of current tracers that may be configured. Function call tracer to trace all kernel functions. - "function_graph_tracer" + "function_graph" Similar to the function tracer except that the function tracer probes the functions on their entry -- cgit v1.2.3