Impact: better handling of CPU buffer start annotation
Because of the confusion with the per CPU buffers wrapping where
one CPU might be more active at the end of the trace than the other
CPUs causing that one CPU to have a shorter history. Kernel
developers were confused by the "missing" data of that one CPU
at the beginning of the trace output. An annotation was added to
the trace output to show that the buffer had started:
# tracer: function
#
# TASK-PID CPU# TIMESTAMP FUNCTION
# | | | | |
##### CPU 3 buffer started ####
<idle>-0 [003] 158.192959: smp_apic_timer_interrupt
[...]
<idle>-0 [003] 161.556520: default_idle
##### CPU 1 buffer started ####
<idle>-0 [001] 161.592494: hrtimer_force_reprogram
[etc]
But this annotation gets a bit messy when tracers do not fill the
buffers. This patch does a couple of things:
One) it adds a flag to trace_options to disable these annotations
Two) it does not annotate if the tracer did not overflow its buffer.
This makes the output much cleaner.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: rename file /debug/tracing/iter_ctrl to /debug/tracing/trace_options
The original ftrace had a file called "iter_ctrl" that would control
the way the output was iterated. But this file grew into a catch all
for different trace options. This patch renames the file from iter_ctrl
to trace_options to reflect this change.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: change the units of buffer_size_kb to kilobytes
This patch changes the units of the buffer_size_kb file to kilobytes.
Reading and writing to the file uses kilobytes as units. To help
users to know what units are used, the output of the file now
looks like:
# cat /debug/tracing/buffer_size_kb
1408
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: rename of debugfs file trace_entries to buffer_size_kb
The original ftrace had fixed size entries, and the number of entries
was shown and modified via the file called trace_entries. By converting
to the unified trace buffer, we now allow for variable size entries
which makes the meaning of trace_entries pointless.
Since trace_size might be confused to the size of the trace, this patch
names it "buffer_size_kb" (thanks to Arjan van de Ven for this idea).
[ mingo@elte.hu: changed from buffer_size to buffer_size_kb ]
( Note, the units are still bytes - the next patch changes that,
to keep the wide rename patch separate from the unit-change patch. )
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: File name change of trace_unlikely.c
The "unlikely" name for the tracer is quite ugly. We renamed all the
parts of it to "branch" and now it is time to rename the file too.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: added new branch tracer
Currently the tracing of branch profiling (unlikelys and likelys hit)
is only activated by the iter_ctrl. This patch adds a tracer called
"branch" that will just trace the branch profiling. The advantage
of adding this tracer is that it can be added to the ftrace selftests
on startup.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: rename of iter_ctrl unlikely to branch
The unlikely name is ugly. This patch converts the iter_ctrl command
"unlikely" and "nounlikely" to "branch" and "nobranch" respectively.
It also renames a lot of internal functions to use "branch" instead
of "unlikely".
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: name change of unlikely tracer and profiler
Ingo Molnar suggested changing the config from UNLIKELY_PROFILE
to BRANCH_PROFILING. I never did like the "unlikely" name so I
went one step farther, and renamed all the unlikely configurations
to a "BRANCH" variant.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Steve suggested the to change the output from this:
> bash-3471 [003] 357.014755: [ MISS ] sched_info_dequeued:sched_stats.h:177
> bash-3471 [003] 357.014756: [ .... ] update_curr:sched_fair.c:489
> bash-3471 [003] 357.014758: [ .... ] calc_delta_fair:sched_fair.c:411
to this:
> bash-3471 [003] 357.014755: [ MISS ] sched_info_dequeued:sched_stats.h:177
> bash-3471 [003] 357.014756: [ ok ] update_curr:sched_fair.c:489
> bash-3471 [003] 357.014758: [ ok ] calc_delta_fair:sched_fair.c:411
as it makes it clearer to the user what it means exactly.
Acked-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: modify the tracer output, to make it a bit easier to read
Change the output from:
> bash-3471 [003] 357.014755: [INCORRECT] sched_info_dequeued:sched_stats.h:177
> bash-3471 [003] 357.014756: [correct] update_curr:sched_fair.c:489
> bash-3471 [003] 357.014758: [correct] calc_delta_fair:sched_fair.c:411
to:
> bash-3471 [003] 357.014755: [ MISS ] sched_info_dequeued:sched_stats.h:177
> bash-3471 [003] 357.014756: [ .... ] update_curr:sched_fair.c:489
> bash-3471 [003] 357.014758: [ .... ] calc_delta_fair:sched_fair.c:411
it's good to have fields aligned vertically, and the only important
information is a prediction miss, so display only that information.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: new likely/unlikely branch tracer
This patch adds a way to record the instances of the likely() and unlikely()
branch condition annotations.
When "unlikely" is set in /debugfs/tracing/iter_ctrl the unlikely conditions
will be added to any of the ftrace tracers. The change takes effect when
a new tracer is passed into the current_tracer file.
For example:
bash-3471 [003] 357.014755: [INCORRECT] sched_info_dequeued:sched_stats.h:177
bash-3471 [003] 357.014756: [correct] update_curr:sched_fair.c:489
bash-3471 [003] 357.014758: [correct] calc_delta_fair:sched_fair.c:411
bash-3471 [003] 357.014759: [correct] account_group_exec_runtime:sched_stats.h:356
bash-3471 [003] 357.014761: [correct] update_curr:sched_fair.c:489
bash-3471 [003] 357.014763: [INCORRECT] calc_delta_fair:sched_fair.c:411
bash-3471 [003] 357.014765: [correct] calc_delta_mine:sched.c:1279
Which shows the normal tracer heading, as well as whether the condition was
correct "[correct]" or was mistaken "[INCORRECT]", followed by the function,
file name and line number.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: new unlikely/likely profiler
Andrew Morton recently suggested having an in-kernel way to profile
likely and unlikely macros. This patch achieves that goal.
When configured, every(*) likely and unlikely macro gets a counter attached
to it. When the condition is hit, the hit and misses of that condition
are recorded. These numbers can later be retrieved by:
/debugfs/tracing/profile_likely - All likely markers
/debugfs/tracing/profile_unlikely - All unlikely markers.
# cat /debug/tracing/profile_unlikely | head
correct incorrect % Function File Line
------- --------- - -------- ---- ----
2167 0 0 do_arch_prctl process_64.c 832
0 0 0 do_arch_prctl process_64.c 804
2670 0 0 IS_ERR err.h 34
71230 5693 7 __switch_to process_64.c 673
76919 0 0 __switch_to process_64.c 639
43184 33743 43 __switch_to process_64.c 624
12740 64181 83 __switch_to process_64.c 594
12740 64174 83 __switch_to process_64.c 590
# cat /debug/tracing/profile_unlikely | \
awk '{ if ($3 > 25) print $0; }' |head -20
44963 35259 43 __switch_to process_64.c 624
12762 67454 84 __switch_to process_64.c 594
12762 67447 84 __switch_to process_64.c 590
1478 595 28 syscall_get_error syscall.h 51
0 2821 100 syscall_trace_leave ptrace.c 1567
0 1 100 native_smp_prepare_cpus smpboot.c 1237
86338 265881 75 calc_delta_fair sched_fair.c 408
210410 108540 34 calc_delta_mine sched.c 1267
0 54550 100 sched_info_queued sched_stats.h 222
51899 66435 56 pick_next_task_fair sched_fair.c 1422
6 10 62 yield_task_fair sched_fair.c 982
7325 2692 26 rt_policy sched.c 144
0 1270 100 pre_schedule_rt sched_rt.c 1261
1268 48073 97 pick_next_task_rt sched_rt.c 884
0 45181 100 sched_info_dequeued sched_stats.h 177
0 15 100 sched_move_task sched.c 8700
0 15 100 sched_move_task sched.c 8690
53167 33217 38 schedule sched.c 4457
0 80208 100 sched_info_switch sched_stats.h 270
30585 49631 61 context_switch sched.c 2619
# cat /debug/tracing/profile_likely | awk '{ if ($3 > 25) print $0; }'
39900 36577 47 pick_next_task sched.c 4397
20824 15233 42 switch_mm mmu_context_64.h 18
0 7 100 __cancel_work_timer workqueue.c 560
617 66484 99 clocksource_adjust timekeeping.c 456
0 346340 100 audit_syscall_exit auditsc.c 1570
38 347350 99 audit_get_context auditsc.c 732
0 345244 100 audit_syscall_entry auditsc.c 1541
38 1017 96 audit_free auditsc.c 1446
0 1090 100 audit_alloc auditsc.c 862
2618 1090 29 audit_alloc auditsc.c 858
0 6 100 move_masked_irq migration.c 9
1 198 99 probe_sched_wakeup trace_sched_switch.c 58
2 2 50 probe_wakeup trace_sched_wakeup.c 227
0 2 100 probe_wakeup_sched_switch trace_sched_wakeup.c 144
4514 2090 31 __grab_cache_page filemap.c 2149
12882 228786 94 mapping_unevictable pagemap.h 50
4 11 73 __flush_cpu_slab slub.c 1466
627757 330451 34 slab_free slub.c 1731
2959 61245 95 dentry_lru_del_init dcache.c 153
946 1217 56 load_elf_binary binfmt_elf.c 904
102 82 44 disk_put_part genhd.h 206
1 1 50 dst_gc_task dst.c 82
0 19 100 tcp_mss_split_point tcp_output.c 1126
As you can see by the above, there's a bit of work to do in rethinking
the use of some unlikelys and likelys. Note: the unlikely case had 71 hits
that were more than 25%.
Note: After submitting my first version of this patch, Andrew Morton
showed me a version written by Daniel Walker, where I picked up
the following ideas from:
1) Using __builtin_constant_p to avoid profiling fixed values.
2) Using __FILE__ instead of instruction pointers.
3) Using the preprocessor to stop all profiling of likely
annotations from vsyscall_64.c.
Thanks to Andrew Morton, Arjan van de Ven, Theodore Tso and Ingo Molnar
for their feed back on this patch.
(*) Not ever unlikely is recorded, those that are used by vsyscalls
(a few of them) had to have profiling disabled.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Theodore Tso <tytso@mit.edu>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: deadlock fix in ring_buffer_read_start
The ring_buffer_iter_reset was called from ring_buffer_read_start
where both grabbed the reader_lock.
This patch separates out the internals of ring_buffer_iter_reset
to its own function so that both APIs may grab the reader_lock.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: disable preemption when calling sched_clock()
The ring_buffer_time_stamp still uses sched_clock as its counter.
But it is a bug to call it with preemption enabled. This requirement
should not be pushed to the ring_buffer_time_stamp callers, so
the ring_buffer_time_stamp needs to disable preemption when calling
sched_clock.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: Cleanups on the boot tracer and ftrace
This patch bring some cleanups about the boot tracer headers. The
functions and structures of this tracer have nothing related to ftrace
and should have so their own header file.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: Restructure WARN_ONs in ring_buffer.c
The current WARN_ON macros in ring_buffer.c are quite ugly.
This patch cleans them up and uses a single RB_WARN_ON that returns
the value of the condition. This allows the caller to abort the
function if the condition is true.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: enable/disable ring buffer recording API added
Several kernel developers have requested that there be a way to stop
recording into the ring buffers with a simple switch that can also
be enabled from userspace. This patch addes a new kernel API to the
ring buffers called:
tracing_on()
tracing_off()
When tracing_off() is called, all ring buffers will not be able to record
into their buffers.
tracing_on() will enable the ring buffers again.
These two act like an on/off switch. That is, there is no counting of the
number of times tracing_off or tracing_on has been called.
A new file is added to the debugfs/tracing directory called
tracing_on
This allows for userspace applications to also flip the switch.
echo 0 > debugfs/tracing/tracing_on
disables the tracing.
echo 1 > /debugfs/tracing/tracing_on
enables it.
Note, this does not disable or enable any tracers. It only sets or clears
a flag that needs to be set in order for the ring buffers to write to
their buffers. It is a global flag, and affects all ring buffers.
The buffers start out with tracing_on enabled.
There are now three flags that control recording into the buffers:
tracing_on: which affects all ring buffer tracers.
buffer->record_disabled: which affects an allocated buffer, which may be set
if an anomaly is detected, and tracing is disabled.
cpu_buffer->record_disabled: which is set by tracing_stop() or if an
anomaly is detected. tracing_start can not reenable this if
an anomaly occurred.
The userspace debugfs/tracing/tracing_enabled is implemented with
tracing_stop() but the user space code can not enable it if the kernel
called tracing_stop().
Userspace can enable the tracing_on even if the kernel disabled it.
It is just a switch used to stop tracing if a condition was hit.
tracing_on is not for protecting critical areas in the kernel nor is
it for stopping tracing if an anomaly occurred. This is because userspace
can reenable it at any time.
Side effect: With this patch, I discovered a dead variable in ftrace.c
called tracing_on. This patch removes it.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Impact: serialize reader accesses to individual CPU ring buffers
The code in the ring buffer expects only one reader at a time, but currently
it puts that requirement on the caller. This is not strong enough, and this
patch adds a "reader_lock" that serializes the access to the reader API
of the ring buffer.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: add new tracing plugin which can trace full (entry+exit) function calls
This tracer uses the low level function return ftrace plugin to
measure the execution time of the kernel functions.
The first field is the caller of the function, the second is the
measured function, and the last one is the execution time in
nanoseconds.
- v3:
- HAVE_FUNCTION_RET_TRACER have been added. Each arch that support ftrace return
should enable it.
- ftrace_return_stub becomes ftrace_stub.
- CONFIG_FUNCTION_RET_TRACER depends now on CONFIG_FUNCTION_TRACER
- Return traces printing can be used for other tracers on trace.c
- Adapt to the new tracing API (no more ctrl_update callback)
- Correct the check of "disabled" during insertion.
- Minor changes...
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This patch replaces most of the BUG_ONs in the ring_buffer code with
RB_WARN_ON variants. It adds some more variants as needed for the
replacement. This lets the buffer die nicely and still warn the user.
One BUG_ON remains in the code, and that is because it detects a
bad pointer passed in by the calling function, and not a bug by
the ring buffer code itself.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: stop ftrace_special from recursion
The ftrace_special is used to help debug areas of the kernel.
Because of this, if it is put in certain locations, the fact that
it allows recursion can become a problem if the kernel developer
using does not realize that.
This patch changes ftrace_special to not allow recursion into itself
to make it more robust.
It also changes from preempt disable interrupts disable to prevent
any loss of trace entries.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: removal of unnecessary looping
The lockless part of the ring buffer allows for reentry into the code
from interrupts. A timestamp is taken, a test is preformed and if it
detects that an interrupt occurred that did tracing, it tries again.
The problem arises if the timestamp code itself causes a trace.
The detection will detect this and loop again. The difference between
this and an interrupt doing tracing, is that this will fail every time,
and cause an infinite loop.
Currently, we test if the loop happens 1000 times, and if so, it will
produce a warning and disable the ring buffer.
The problem with this approach is that it makes it difficult to perform
some types of tracing (tracing the timestamp code itself).
Each trace entry has a delta timestamp from the previous entry.
If a trace entry is reserved but and interrupt occurs and traces before
the previous entry is commited, the delta timestamp for that entry will
be zero. This actually makes sense in terms of tracing, because the
interrupt entry happened before the preempted entry was commited, so
one may consider the two happening at the same time. The order is
still preserved in the buffer.
With this idea, instead of trying to get a new timestamp if an interrupt
made it in between the timestamp and the test, the entry could simply
make the delta zero and continue. This will prevent interrupts or
tracers in the timer code from causing the above loop.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Impact: fix for bug on resize
This patch addresses the bug found here:
http://bugzilla.kernel.org/show_bug.cgi?id=11996
When ftrace converted to the new unified trace buffer, the resizing of
the buffer was not protected as much as it was originally. If tracing
is performed while the resize occurs, then the buffer can be corrupted.
This patch disables all ftrace buffer modifications before a resize
takes place.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Impact: change in trace output
Because the trace buffers are per cpu ring buffers, the start of
the trace can be confusing. If one CPU is very active at the
end of the trace, its history will not go as far back as the
other CPU traces. This means that output for a particular CPU
may not appear for the first part of a trace.
To help annotate what is happening, and to prevent any more
confusion, this patch adds a line that annotates the start of
a CPU buffer output.
For example:
automount-3495 [001] 184.596443: dnotify_parent <-vfs_write
[...]
automount-3495 [001] 184.596449: dput <-path_put
automount-3496 [002] 184.596450: down_read_trylock <-do_page_fault
[...]
sshd-3497 [001] 184.597069: up_read <-do_page_fault
<idle>-0 [000] 184.597074: __exit_idle <-exit_idle
[...]
automount-3496 [002] 184.597257: filemap_fault <-__do_fault
<idle>-0 [003] 184.597261: exit_idle <-smp_apic_timer_interrupt
Note, parsers of a trace output should always ignore any lines that
start with a '#'.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: preemptoff not tested in selftest
Due to the BKL not being preemptable anymore, the selftest of the
preemptoff code can not be tested. It requires that it is called
with preemption enabled, but since the BKL is held, that is no
longer the case.
This patch simply skips those tests if it detects that the context
is not preemptable. The following will now show up in the tests:
Testing tracer preemptoff: can not test ... force PASSED
Testing tracer preemptirqsoff: can not test ... force PASSED
When the BKL is removed, or it becomes preemptable once again, then
the tests will be performed.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: remove obsolete variable in trace_array structure
With the new start / stop method of ftrace, the ctrl variable
in the trace_array structure is now obsolete. Remove it.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: Remove the ctrl_update tracer method
With the new quick start/stop method of tracing, the ctrl_update
method is out of date.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: have the ftrace_printk enabled on startup
It is confusing to have to "echo trace_printk > /debug/tracing/iter_ctrl"
after adding ftrace_printk in the kernel.
Currently the trace_printk is set to off by default. ftrace_printk
should only be in open kernel code when used for debugging, and thus
it should be enabled by default.
It may also be used to record data within a tracer, but those ftrace_printks
should be within wrappers that are either enabled by trace_points or
have a variable protecting the code path from being entered when the
tracer is disabled.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: fix to irqsoff tracer output
In converting to the new start / stop ftrace handling, the irqsoff
tracer start called the irqsoff reset function. irqsoff tracer is
not the same as the other traces, and it resets the buffers while
searching for the longest latency.
The reset that the irqsoff stop method calls disables the function
tracing. That means that, by starting the tracer, the function
tracer is disabled incorrectly.
This patch simply removes the call to reset which keeps the function
tracing enabled. Reset is not needed for the irqsoff stop method.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: fix for sched_switch that broke dynamic ftrace startup
The commit: tracing/fastboot: use sched switch tracer from boot tracer
broke the API of the sched_switch trace. The use of the
tracing_start/stop_cmdline record is for only recording the cmdline,
NOT recording the schedule switches themselves.
Seeing that the boot tracer broke the API to do something that it
wanted, this patch adds a new interface for the API while
puting back the original interface of the old API.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: boot tracer startup modified
The boot tracer calls into some of the schedule tracing private functions
that should not be exported. This patch cleans it up, and makes
way for further changes in the ftrace infrastructure.
This patch adds a api to assign a tracer array to the schedule
context switch tracer.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: fix of output of set_ftrace_filter
Commit ftrace: do not show freed records in available_filter_functions
Removed a bit too much from the set_ftrace_filter code, where we now see
all functions in the set_ftrace_filter file even when we set a filter.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: no lockdep debugging of ring buffer
The problem with running lockdep on the ring buffer is that the
ring buffer is the core infrastructure of ftrace. What happens is
that the tracer will start tracing the lockdep code while lockdep
is testing the ring buffers locks. This can cause lockdep to
fail due to testing cases that have not fully finished their
locking transition.
This patch converts the spin locks used by the ring buffer back
into raw spin locks which lockdep does not check.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: change where tracing is started up and stopped
Currently, when a new tracer is selected via echo'ing a tracer name into
the current_tracer file, the startup is only done if tracing_enabled is
set to one. If tracing_enabled is changed to zero (by echo'ing 0 into
the tracing_enabled file) a full shutdown is performed.
The full startup and shutdown of a tracer can be expensive and the
user can lose out traces when echo'ing in 0 to the tracing_enabled file,
because the process takes too long. There can also be places that
the user would like to start and stop the tracer several times and
doing the full startup and shutdown of a tracer might be too expensive.
This patch performs the full startup and shutdown when a tracer is
selected. It also adds a way to do a quick start or stop of a tracer.
The quick version is just a flag that prevents the tracing from
taking place, but the overhead of the code is still there.
For example, the startup of a tracer may enable tracepoints, or enable
the function tracer. The stop and start will just set a flag to
have the tracer ignore the calls when the tracepoint or function trace
is called. The overhead of the tracer may still be present when
the tracer is stopped, but no tracing will occur. Setting the tracer
to the 'nop' tracer (or any other tracer) will perform the shutdown
of the tracer which will disable the tracepoint or disable the
function tracer.
The tracing_enabled file will simply start or stop tracing.
This change is all internal. The end result for the user should be the same
as before. If tracing_enabled is not set, no trace will happen.
If tracing_enabled is set, then the trace will happen. The tracing_enabled
variable is static between tracers. Enabling tracing_enabled and
going to another tracer will keep tracing_enabled enabled. Same
is true with disabling tracing_enabled.
This patch will now provide a fast start/stop method to the users
for enabling or disabling tracing.
Note: There were two methods to the struct tracer that were never
used: The methods start and stop. These were to be used as a hook
to the reading of the trace output, but ended up not being
necessary. These two methods are now used to enable the start
and stop of each tracer, in case the tracer needs to do more than
just not write into the buffer. For example, the irqsoff tracer
must stop recording max latencies when tracing is stopped.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: add way to quickly start stop tracing from the kernel
This patch adds a soft stop and start to the trace. This simply
disables function tracing via the ftrace_disabled flag, and
disables the trace buffers to prevent recording. The tracing
code may still be executed, but the trace will not be recorded.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: quick start and stop of function tracer
This patch adds a way to disable the function tracer quickly without
the need to run kstop_machine. It adds a new variable called
function_trace_stop which will stop the calls to functions from mcount
when set. This is just an on/off switch and does not handle recursion
like preempt_disable().
It's main purpose is to help other tracers/debuggers start and stop tracing
fuctions without the need to call kstop_machine.
The config option HAVE_FUNCTION_TRACE_MCOUNT_TEST is added for archs
that implement the testing of the function_trace_stop in the mcount
arch dependent code. Otherwise, the test is done in the C code.
x86 is the only arch at the moment that supports this.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
In 777e208d40 we changed from outputting
field->cpu (a char) to iter->cpu (unsigned int), increasing the resulting
structure size by 3 bytes.
Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: fix boot tracer + sched tracer coupling bug
Fix a bug that made the sched_switch tracer unable to run
if set as the current_tracer after the boot tracer.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: cleanup
This patch applies some corrections suggested by Steven Rostedt.
Change the type of shed_ref into int since it is used
into a Mutex, we don't need it anymore as an atomic
variable in the sched_switch tracer.
Also change the name of the register mutex.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: enhance boot trace output with scheduling events
Use the sched_switch tracer from the boot tracer.
We also can trace schedule events inside the initcalls.
Sched tracing is disabled after the initcall has finished and
then reenabled before the next one is started.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
