03 Nov, 2015
1 commit
-
Make ring_buffer_empty() and ring_buffer_empty_cpu() return bool.
No functional change.
Link: http://lkml.kernel.org/r/1443537816-5788-5-git-send-email-bywxiaobai@163.com
Signed-off-by: Yaowei Bai
Signed-off-by: Steven Rostedt
11 Nov, 2014
1 commit
-
On a !PREEMPT kernel, attempting to use trace-cmd results in a soft
lockup:# trace-cmd record -e raw_syscalls:* -F false
NMI watchdog: BUG: soft lockup - CPU#0 stuck for 22s! [trace-cmd:61]
...
Call Trace:
[] ? __wake_up_common+0x90/0x90
[] wait_on_pipe+0x35/0x40
[] tracing_buffers_splice_read+0x2e3/0x3c0
[] ? tracing_stats_read+0x2a0/0x2a0
[] ? _raw_spin_unlock+0x2b/0x40
[] ? do_read_fault+0x21b/0x290
[] ? handle_mm_fault+0x2ba/0xbd0
[] ? trace_event_buffer_lock_reserve+0x40/0x80
[] ? trace_buffer_lock_reserve+0x22/0x60
[] ? trace_event_buffer_lock_reserve+0x40/0x80
[] do_splice_to+0x6d/0x90
[] SyS_splice+0x7c1/0x800
[] tracesys_phase2+0xd3/0xd8The problem is this: tracing_buffers_splice_read() calls
ring_buffer_wait() to wait for data in the ring buffers. The buffers
are not empty so ring_buffer_wait() returns immediately. But
tracing_buffers_splice_read() calls ring_buffer_read_page() with full=1,
meaning it only wants to read a full page. When the full page is not
available, tracing_buffers_splice_read() tries to wait again with
ring_buffer_wait(), which again returns immediately, and so on.Fix this by adding a "full" argument to ring_buffer_wait() which will
make ring_buffer_wait() wait until the writer has left the reader's
page, i.e. until full-page reads will succeed.Link: http://lkml.kernel.org/r/1415645194-25379-1-git-send-email-rabin@rab.in
Cc: stable@vger.kernel.org # 3.16+
Fixes: b1169cc69ba9 ("tracing: Remove mock up poll wait function")
Signed-off-by: Rabin Vincent
Signed-off-by: Steven Rostedt
10 Jun, 2014
1 commit
-
The per_cpu buffers are created one per possible CPU. But these do
not mean that those CPUs are online, nor do they even exist.With the addition of the ring buffer polling, it assumes that the
caller polls on an existing buffer. But this is not the case if
the user reads trace_pipe from a CPU that does not exist, and this
causes the kernel to crash.Simple fix is to check the cpu against buffer bitmask against to see
if the buffer was allocated or not and return -ENODEV if it is
not.More updates were done to pass the -ENODEV back up to userspace.
Link: http://lkml.kernel.org/r/5393DB61.6060707@oracle.com
Reported-by: Sasha Levin
Cc: stable@vger.kernel.org # 3.10+
Signed-off-by: Steven Rostedt
15 Mar, 2013
1 commit
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Move the logic to wake up on ring buffer data into the ring buffer
code itself. This simplifies the tracing code a lot and also has the
added benefit that waiters on one of the instance buffers can be woken
only when data is added to that instance instead of data added to
any instance.Signed-off-by: Steven Rostedt
31 Jan, 2013
1 commit
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Add a stat about the number of events read from the ring buffer:
# cat /debug/tracing/per_cpu/cpu0/stats
entries: 39869
overrun: 870512
commit overrun: 0
bytes: 1449912
oldest event ts: 6561.368690
now ts: 6565.246426
dropped events: 0
read events: 112
02 Nov, 2012
1 commit
-
ring_buffer_oldest_event_ts() should return a value of u64 type, because
ring_buffer_per_cpu->buffer_page->buffer_data_page->time_stamp is u64 type.Link: http://lkml.kernel.org/r/1349998076-15495-5-git-send-email-dhsharp@google.com
Cc: Frederic Weisbecker
Cc: Vaibhav Nagarnaik
Signed-off-by: Yoshihiro YUNOMAE
Signed-off-by: David Sharp
Signed-off-by: Steven Rostedt
01 Nov, 2012
1 commit
-
The existing 'overrun' counter is incremented when the ring
buffer wraps around, with overflow on (the default). We wanted
a way to count requests lost from the buffer filling up with
overflow off, too. I decided to add a new counter instead
of retro-fitting the existing one because it seems like a
different statistic to count conceptually, and also because
of how the code was structured.Link: http://lkml.kernel.org/r/1310765038-26399-1-git-send-email-slavapestov@google.com
Signed-off-by: Slava Pestov
Signed-off-by: Steven Rostedt
24 Apr, 2012
1 commit
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Add a debugfs entry under per_cpu/ folder for each cpu called
buffer_size_kb to control the ring buffer size for each CPU
independently.If the global file buffer_size_kb is used to set size, the individual
ring buffers will be adjusted to the given size. The buffer_size_kb will
report the common size to maintain backward compatibility.If the buffer_size_kb file under the per_cpu/ directory is used to
change buffer size for a specific CPU, only the size of the respective
ring buffer is updated. When tracing/buffer_size_kb is read, it reports
'X' to indicate that sizes of per_cpu ring buffers are not equivalent.Link: http://lkml.kernel.org/r/1328212844-11889-1-git-send-email-vnagarnaik@google.com
Cc: Frederic Weisbecker
Cc: Michael Rubin
Cc: David Sharp
Cc: Justin Teravest
Signed-off-by: Vaibhav Nagarnaik
Signed-off-by: Steven Rostedt
23 Feb, 2012
1 commit
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As the ring-buffer code is being used by other facilities in the
kernel, having tracing_on file disable *all* buffers is not a desired
affect. It should only disable the ftrace buffers that are being used.Move the code into the trace.c file and use the buffer disabling
for tracing_on() and tracing_off(). This way only the ftrace buffers
will be affected by them and other kernel utilities will not be
confused to why their output suddenly stopped.Signed-off-by: Steven Rostedt
31 Aug, 2011
1 commit
-
The stats file under per_cpu folder provides the number of entries,
overruns and other statistics about the CPU ring buffer. However, the
numbers do not provide any indication of how full the ring buffer is in
bytes compared to the overall size in bytes. Also, it is helpful to know
the rate at which the cpu buffer is filling up.This patch adds an entry "bytes: " in printed stats for per_cpu ring
buffer which provides the actual bytes consumed in the ring buffer. This
field includes the number of bytes used by recorded events and the
padding bytes added when moving the tail pointer to next page.It also adds the following time stamps:
"oldest event ts:" - the oldest timestamp in the ring buffer
"now ts:" - the timestamp at the time of readingThe field "now ts" provides a consistent time snapshot to the userspace
when being read. This is read from the same trace clock used by tracing
event timestamps.Together, these values provide the rate at which the buffer is filling
up, from the formula:
bytes / (now_ts - oldest_event_ts)Signed-off-by: Vaibhav Nagarnaik
Cc: Michael Rubin
Cc: David Sharp
Link: http://lkml.kernel.org/r/1313531179-9323-3-git-send-email-vnagarnaik@google.com
Signed-off-by: Steven Rostedt
15 Jun, 2011
1 commit
-
The tracing ring buffer is a group of per-cpu ring buffers where
allocation and logging is done on a per-cpu basis. The events that are
generated on a particular CPU are logged in the corresponding buffer.
This is to provide wait-free writes between CPUs and good NUMA node
locality while accessing the ring buffer.However, the allocation routines consider NUMA locality only for buffer
page metadata and not for the actual buffer page. This causes the pages
to be allocated on the NUMA node local to the CPU where the allocation
routine is running at the time.This patch fixes the problem by using a NUMA node specific allocation
routine so that the pages are allocated from a NUMA node local to the
logging CPU.I tested with the getuid_microbench from autotest. It is a simple binary
that calls getuid() in a loop and measures the average time for the
syscall to complete. The following command was used to test:
$ getuid_microbench 1000000Compared the numbers found on kernel with and without this patch and
found that logging latency decreases by 30-50 ns/call.
tracing with non-NUMA allocation - 569 ns/call
tracing with NUMA allocation - 512 ns/callSigned-off-by: Vaibhav Nagarnaik
Cc: Frederic Weisbecker
Cc: Ingo Molnar
Cc: Michael Rubin
Cc: David Sharp
Link: http://lkml.kernel.org/r/1304470602-20366-1-git-send-email-vnagarnaik@google.com
Signed-off-by: Steven Rostedt
10 Mar, 2011
1 commit
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Add an "overwrite" trace_option for ftrace to control whether the buffer should
be overwritten on overflow or not. The default remains to overwrite old events
when the buffer is full. This patch adds the option to instead discard newest
events when the buffer is full. This is useful to get a snapshot of traces just
after enabling traces. Dropping the current event is also a simpler code path.Signed-off-by: David Sharp
LKML-Reference:
Signed-off-by: Steven Rostedt
21 Oct, 2010
1 commit
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The ring_buffer_event_time_delta() static inline function does not
have any users. Remove it.Signed-off-by: Steven Rostedt
28 Apr, 2010
1 commit
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When performing a non-consuming read, a synchronize_sched() is
performed once for every cpu which is actively tracing.This is very expensive, and can make it take several seconds to open
up the 'trace' file with lots of cpus.Only one synchronize_sched() call is actually necessary. What is
desired is for all cpus to see the disabling state change. So we
transform the existing sequence:for_each_cpu() {
ring_buffer_read_start();
}where each ring_buffer_start() call performs a synchronize_sched(),
into the following:for_each_cpu() {
ring_buffer_read_prepare();
}
ring_buffer_read_prepare_sync();
for_each_cpu() {
ring_buffer_read_start();
}wherein only the single ring_buffer_read_prepare_sync() call needs to
do the synchronize_sched().The first phase, via ring_buffer_read_prepare(), allocates the 'iter'
memory and increments ->record_disabled.In the second phase, ring_buffer_read_prepare_sync() makes sure this
->record_disabled state is visible fully to all cpus.And in the final third phase, the ring_buffer_read_start() calls reset
the 'iter' objects allocated in the first phase since we now know that
none of the cpus are adding trace entries any more.This makes openning the 'trace' file nearly instantaneous on a
sparc64 Niagara2 box with 128 cpus tracing.Signed-off-by: David S. Miller
LKML-Reference:
Signed-off-by: Steven Rostedt
01 Apr, 2010
1 commit
-
Currently, when the ring buffer drops events, it does not record
the fact that it did so. It does inform the writer that the event
was dropped by returning a NULL event, but it does not put in any
place holder where the event was dropped.This is not a trivial thing to add because the ring buffer mostly
runs in overwrite (flight recorder) mode. That is, when the ring
buffer is full, new data will overwrite old data.In a produce/consumer mode, where new data is simply dropped when
the ring buffer is full, it is trivial to add the placeholder
for dropped events. When there's more room to write new data, then
a special event can be added to notify the reader about the dropped
events.But in overwrite mode, any new write can overwrite events. A place
holder can not be inserted into the ring buffer since there never
may be room. A reader could also come in at anytime and miss the
placeholder.Luckily, the way the ring buffer works, the read side can find out
if events were lost or not, and how many events. Everytime a write
takes place, if it overwrites the header page (the next read) it
updates a "overrun" variable that keeps track of the number of
lost events. When a reader swaps out a page from the ring buffer,
it can record this number, perfom the swap, and then check to
see if the number changed, and take the diff if it has, which would be
the number of events dropped. This can be stored by the reader
and returned to callers of the reader.Since the reader page swap will fail if the writer moved the head
page since the time the reader page set up the swap, this gives room
to record the overruns without worrying about races. If the reader
sets up the pages, records the overrun, than performs the swap,
if the swap succeeds, then the overrun variable has not been
updated since the setup before the swap.For binary readers of the ring buffer, a flag is set in the header
of each sub page (sub buffer) of the ring buffer. This flag is embedded
in the size field of the data on the sub buffer, in the 31st bit (the size
can be 32 or 64 bits depending on the architecture), but only 27
bits needs to be used for the actual size (less actually).We could add a new field in the sub buffer header to also record the
number of events dropped since the last read, but this will change the
format of the binary ring buffer a bit too much. Perhaps this change can
be made if the information on the number of events dropped is considered
important enough.Note, the notification of dropped events is only used by consuming reads
or peeking at the ring buffer. Iterating over the ring buffer does not
keep this information because the necessary data is only available when
a page swap is made, and the iterator does not swap out pages.Cc: Robert Richter
Cc: Andi Kleen
Cc: Li Zefan
Cc: Arnaldo Carvalho de Melo
Cc: "Luis Claudio R. Goncalves"
Cc: Frederic Weisbecker
Signed-off-by: Steven Rostedt
05 Sep, 2009
1 commit
-
Since the ability to swap the cpu buffers adds a small overhead to
the recording of a trace, we only want to add it when needed.Only the irqsoff and preemptoff tracers use this feature, and both are
not recommended for production kernels. This patch disables its use
when neither irqsoff nor preemptoff is configured.Signed-off-by: Steven Rostedt
04 Sep, 2009
1 commit
-
The function ring_buffer_event_discard can be used on any item in the
ring buffer, even after the item was committed. This function provides
no safety nets and is very race prone.An item may be safely removed from the ring buffer before it is committed
with the ring_buffer_discard_commit.Since there are currently no users of this function, and because this
function is racey and error prone, this patch removes it altogether.Note, removing this function also allows the counters to ignore
all discarded events (patches will follow).Signed-off-by: Steven Rostedt
08 Jul, 2009
1 commit
-
This patch converts the ring buffers into a completely lockless
buffer recording system. The read side still takes locks since
we still serialize readers. But the writers are the ones that
must be lockless (those can happen in NMIs).The main change is to the "head_page" pointer. We write to the
tail, and read from the head. The "head_page" pointer in the cpu
buffer is now just a reference to where to look. The real head
page is now kept in the head_page->list->prev->next pointer.
That is, in the list head of the previous page we set flags.The list pages are allocated to be aligned such that the lowest
significant bits are always zero pointing to the list. This gives
us play to put in flags to their pointers.bit 0: set when the page is a head page
bit 1: set when the writer is moving the page (for overwrite mode)cmpxchg is used to update the pointer.
When the writer wraps the buffer and the tail meets the head,
in overwrite mode, the writer must move the head page forward.
It first uses cmpxchg to change the pointer flag from 1 to 2.
Once this is done, the reader on another CPU will not take the
page from the buffer.The writers need to protect against interrupts (we don't bother with
disabling interrupts because NMIs are allowed to write too).After the writer sets the pointer flag to 2, it takes care to
manage interrupts coming in. This is discribed in detail within the
comments of the code.Changes in version 2:
- Let reader reset entries value of header page.
- Fix tail page passing commit page on reader page test.
- Always increment entries and write counter in rb_tail_page_update
- Add safety check in rb_set_commit_to_write to break out of infinite loop
- add mask in rb_is_reader_page[ Impact: lock free writing to the ring buffer ]
Signed-off-by: Steven Rostedt
15 Jun, 2009
1 commit
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This gets rid of a heap of false-positive warnings from the tracer
code due to the use of bitfields.[rebased for mainline inclusion]
Signed-off-by: Vegard Nossum
09 Jun, 2009
1 commit
-
On Sun, 7 Jun 2009, Ingo Molnar wrote:
> Testing tracer sched_switch: Starting ring buffer hammer
> PASSED
> Testing tracer sysprof: PASSED
> Testing tracer function: PASSED
> Testing tracer irqsoff:
> =============================================
> PASSED
> Testing tracer preemptoff: PASSED
> Testing tracer preemptirqsoff: [ INFO: possible recursive locking detected ]
> PASSED
> Testing tracer branch: 2.6.30-rc8-tip-01972-ge5b9078-dirty #5760
> ---------------------------------------------
> rb_consumer/431 is trying to acquire lock:
> (&cpu_buffer->reader_lock){......}, at: [] ring_buffer_reset_cpu+0x37/0x70
>
> but task is already holding lock:
> (&cpu_buffer->reader_lock){......}, at: [] ring_buffer_consume+0x7e/0xc0
>
> other info that might help us debug this:
> 1 lock held by rb_consumer/431:
> #0: (&cpu_buffer->reader_lock){......}, at: [] ring_buffer_consume+0x7e/0xc0The ring buffer is a generic structure, and can be used outside of
ftrace. If ftrace traces within the use of the ring buffer, it can produce
false positives with lockdep.This patch passes in a static lock key into the allocation of the ring
buffer, so that different ring buffers will have their own lock class.Reported-by: Ingo Molnar
Signed-off-by: Peter Zijlstra
LKML-Reference:[ store key in ring buffer descriptor ]
Signed-off-by: Steven Rostedt
06 May, 2009
1 commit
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The WARN_ON in the ring buffer when a commit is preempted and the
buffer is filled by preceding writes can happen in normal operations.
The WARN_ON makes it look like a bug, not to mention, because
it does not stop tracing and calls printk which can also recurse, this
is prone to deadlock (the WARN_ON is not in a position to recurse).This patch removes the WARN_ON and replaces it with a counter that
can be retrieved by a tracer. This counter is called commit_overrun.While at it, I added a nmi_dropped counter to count any time an NMI entry
is dropped because the NMI could not take the spinlock.[ Impact: prevent deadlock by printing normal case warning ]
Signed-off-by: Steven Rostedt
24 Apr, 2009
1 commit
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RB_MAX_SMALL_DATA = 28bytes is too small for most tracers, it wastes
an 'u32' to save the actually length for events which data size > 28.This fix uses compressed event header and enlarges RB_MAX_SMALL_DATA.
[ Impact: saves about 0%-12.5%(depends on tracer) memory in ring_buffer ]
Signed-off-by: Lai Jiangshan
LKML-Reference:
Signed-off-by: Steven Rostedt
17 Apr, 2009
1 commit
-
Currently, every thing needed to read the binary output from the
ring buffers is available, with the exception of the way the ring
buffers handles itself internally.This patch creates two special files in the debugfs/tracing/events
directory:# cat /debug/tracing/events/header_page
field: u64 timestamp; offset:0; size:8;
field: local_t commit; offset:8; size:8;
field: char data; offset:16; size:4080;# cat /debug/tracing/events/header_event
type : 2 bits
len : 3 bits
time_delta : 27 bits
array : 32 bitspadding : type == 0
time_extend : type == 1
data : type == 3This is to allow a userspace app to see if the ring buffer format changes
or not.[ Impact: allow userspace apps to know of ringbuffer format changes ]
Signed-off-by: Steven Rostedt
14 Apr, 2009
1 commit
-
The ring_buffer_discard_commit is similar to ring_buffer_event_discard
but it can only be done on an event that has yet to be commited.
Unpredictable results can happen otherwise.The main difference between ring_buffer_discard_commit and
ring_buffer_event_discard is that ring_buffer_discard_commit will try
to free the data in the ring buffer if nothing has addded data
after the reserved event. If something did, then it acts almost the
same as ring_buffer_event_discard followed by a
ring_buffer_unlock_commit.Note, either ring_buffer_commit_discard and ring_buffer_unlock_commit
can be called on an event, not both.This commit also exports both discard functions to be usable by
GPL modules.Signed-off-by: Steven Rostedt
Signed-off-by: Ingo Molnar
23 Mar, 2009
1 commit
-
This patch overloads RINGBUF_TYPE_PADDING to provide a way to discard
events from the ring buffer, for the event-filtering mechanism
introduced in a subsequent patch.I did the initial version but thanks to Steven Rostedt for adding
the parts that actually made it work. ;-)Signed-off-by: Tom Zanussi
Acked-by: Frederic Weisbecker
Signed-off-by: Ingo Molnar
18 Mar, 2009
1 commit
-
This patch adds a new function called ring_buffer_set_clock that
allows a tracer to assign its own clock source to the buffer.Signed-off-by: Steven Rostedt
05 Mar, 2009
1 commit
-
Impact: cleanup
The functions tracing_start/tracing_stop have been moved to kernel.h.
These are not the functions a developer most likely wants to use
when they want to insert a place to stop tracing and restart it from
user space.tracing_start/tracing_stop was created to work with things like
suspend to ram, where even calling smp_processor_id() can crash the
system. The tracing_start/tracing_stop was used to stop the tracer from
doing anything. These are still light weight functions, but add a bit
more overhead to be able to stop the tracers. They also have no interface
back to userland. That is, if the kernel calls tracing_stop, userland
can not start tracing.What a developer most likely wants to use is tracing_on/tracing_off.
These are very light weight functions (simply sets or clears a bit).
These functions just stop recording into the ring buffer. The tracers
don't even know that this happens except that they would receive NULL
from the ring_buffer_lock_reserve function.Also, there's a way for the user land to enable or disable this bit.
In debugfs/tracing/tracing_on, a user may echo "0" (same as tracing_off())
or echo "1" (same as tracing_on()) into this file. This becomes handy when
a kernel developer is debugging and wants tracing to turn off when it
hits an anomaly. Then the developer can examine the trace, and restart
tracing if they want to try again (echo 1 > tracing_on).This patch moves the prototypes for tracing_on/tracing_off to kernel.h
and comments their use, so that a kernel developer will know how
to use them.Signed-off-by: Steven Rostedt
04 Mar, 2009
1 commit
-
The ring_buffer_read_page was broken if it were to only copy part
of the page. This patch fixes that up as well as adds a parameter
to allow a length field, in order to only copy part of the buffer page.Signed-off-by: Steven Rostedt
17 Feb, 2009
1 commit
-
This patch adds the tracing_is_on() interface to tell if the ring
buffer is turned on or not.Signed-off-by: Steven Rostedt
11 Feb, 2009
1 commit
-
Impact: clean up.
Fix typos in the comments.
Signed-off-by: Wenji Huang
Signed-off-by: Steven Rostedt
09 Feb, 2009
1 commit
-
…el/git/rostedt/linux-2.6-trace into tracing/ftrace
Conflicts:
kernel/trace/trace_hw_branches.c
08 Feb, 2009
1 commit
-
tracing_off() is the fastest way to stop recording to the ring buffers.
This may be used in places like panic and die, just before the
ftrace_dump is called.This patch adds the appropriate CPP conditionals to make it a stub
function when the ring buffer is not configured it.Signed-off-by: Steven Rostedt
06 Feb, 2009
1 commit
-
Impact: API change, cleanup
>From ring_buffer_{lock_reserve,unlock_commit}.
$ codiff /tmp/vmlinux.before /tmp/vmlinux.after
linux-2.6-tip/kernel/trace/trace.c:
trace_vprintk | -14
trace_graph_return | -14
trace_graph_entry | -10
trace_function | -8
__ftrace_trace_stack | -8
ftrace_trace_userstack | -8
tracing_sched_switch_trace | -8
ftrace_trace_special | -12
tracing_sched_wakeup_trace | -8
9 functions changed, 90 bytes removed, diff: -90linux-2.6-tip/block/blktrace.c:
__blk_add_trace | -1
1 function changed, 1 bytes removed, diff: -1/tmp/vmlinux.after:
10 functions changed, 91 bytes removed, diff: -91Signed-off-by: Arnaldo Carvalho de Melo
Acked-by: Frédéric Weisbecker
Signed-off-by: Ingo Molnar
31 Dec, 2008
1 commit
-
* 'oprofile-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
oprofile: select RING_BUFFER
ring_buffer: adding EXPORT_SYMBOLs
oprofile: fix lost sample counter
oprofile: remove nr_available_slots()
oprofile: port to the new ring_buffer
ring_buffer: add remaining cpu functions to ring_buffer.h
oprofile: moving cpu_buffer_reset() to cpu_buffer.h
oprofile: adding cpu_buffer_entries()
oprofile: adding cpu_buffer_write_commit()
oprofile: adding cpu buffer r/w access functions
ftrace: remove unused function arg in trace_iterator_increment()
ring_buffer: update description for ring_buffer_alloc()
oprofile: set values to default when creating oprofilefs
oprofile: implement switch/case in buffer_sync.c
x86/oprofile: cleanup IBS init/exit functions in op_model_amd.c
x86/oprofile: reordering IBS code in op_model_amd.c
oprofile: fix typo
oprofile: whitspace changes only
oprofile: update comment for oprofile_add_sample()
oprofile: comment cleanup
10 Dec, 2008
1 commit
-
These functions are not yet in ring_buffer.h though they seems to be
part of the API.Cc: Steven Rostedt
Signed-off-by: Robert Richter
08 Dec, 2008
1 commit
-
Impact: comments cleanup
fix incorrect comments for enum ring_buffer_type
Signed-off-by: Lai Jiangshan
Signed-off-by: Ingo Molnar
03 Dec, 2008
1 commit
-
Impact: new API to ring buffer
This patch adds a new interface into the ring buffer that allows a
page to be read from the ring buffer on a given CPU. For every page
read, one must also be given to allow for a "swap" of the pages.rpage = ring_buffer_alloc_read_page(buffer);
if (!rpage)
goto err;
ret = ring_buffer_read_page(buffer, &rpage, cpu, full);
if (!ret)
goto empty;
process_page(rpage);
ring_buffer_free_read_page(rpage);The caller of these functions must handle any waits that are
needed to wait for new data. The ring_buffer_read_page will simply
return 0 if there is no data, or if "full" is set and the writer
is still on the current page.Signed-off-by: Steven Rostedt
Signed-off-by: Ingo Molnar
23 Nov, 2008
1 commit
-
Impact: feature to permanently disable ring buffer
This patch adds a API to the ring buffer code that will permanently
disable the ring buffer from ever recording. This should only be
called when some serious anomaly is detected, and the system
may be in an unstable state. When that happens, shutting down the
recording to the ring buffers may be appropriate.Signed-off-by: Steven Rostedt
Signed-off-by: Ingo Molnar
12 Nov, 2008
1 commit
-
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
14 Oct, 2008
1 commit
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The old "lock always" scheme had issues with lockdep, and was not very
efficient anyways.This patch does a new design to be partially lockless on writes.
Writes will add new entries to the per cpu pages by simply disabling
interrupts. When a write needs to go to another page than it will
grab the lock.A new "read page" has been added so that the reader can pull out a page
from the ring buffer to read without worrying about the writer writing over
it. This allows us to not take the lock for all reads. The lock is
now only taken when a read needs to go to a new page.This is far from lockless, and interrupts still need to be disabled,
but it is a step towards a more lockless solution, and it also
solves a lot of the issues that were noticed by the first conversion
of ftrace to the ring buffers.Note: the ring_buffer_{un}lock API has been removed.
Signed-off-by: Steven Rostedt
Signed-off-by: Ingo Molnar