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  1. 06 11月, 2008 5 次提交
    • S
      ring-buffer: convert to raw spinlocks · 3e03fb7f
      由 Steven Rostedt 提交于 
      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: NSteven Rostedt <srostedt@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      3e03fb7f
    • S
      ftrace: restructure tracing start/stop infrastructure · 9036990d
      由 Steven Rostedt 提交于 
      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: NSteven Rostedt <srostedt@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      9036990d
    • S
      ftrace: soft tracing stop and start · 0f048701
      由 Steven Rostedt 提交于 
      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: NSteven Rostedt <srostedt@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      0f048701
    • S
      ftrace: add quick function trace stop · 60a7ecf4
      由 Steven Rostedt 提交于 
      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: NSteven Rostedt <srostedt@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      60a7ecf4
    • I
      Merge branch 'tracing/fastboot' into tracing/ftrace · 79c81d22
      由 Ingo Molnar 提交于
      79c81d22
  3. 05 11月, 2008 6 次提交
  5. 04 11月, 2008 5 次提交
    • P
      ftrace: sysctl typo · 3299b4dd
      由 Peter Zijlstra 提交于 
      Impact: fix sysctl name typo

Steve must have needed more coffee ;-)
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      3299b4dd
    • P
      ftrace: sysrq-z to dump the buffers · 69f698ad
      由 Peter Zijlstra 提交于 
      Impact: add SysRq-z support to dump trace buffers

Allows one to force an ftrace dump from sysrq
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: NSteven Rostedt <srostedt@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      69f698ad
    • S
      ftrace: function tracer with irqs disabled · b2a866f9
      由 Steven Rostedt 提交于 
      Impact: disable interrupts during trace entry creation (as opposed to preempt)

To help with performance, I set the ftracer to not disable interrupts,
and only to disable preemption. If an interrupt occurred, it would not
be traced, because the function tracer protects itself from recursion.
This may be faster, but the trace output might miss some traces.

This patch makes the fuction trace disable interrupts, but it also
adds a runtime feature to disable preemption instead. It does this by
having two different tracer functions. When the function tracer is
enabled, it will check to see which version is requested (irqs disabled
or preemption disabled). Then it will use the corresponding function
as the tracer.

Irq disabling is the default behaviour, but if the user wants better
performance, with the chance of missing traces, then they can choose
the preempt disabled version.

Running hackbench 3 times with the irqs disabled and 3 times with
the preempt disabled function tracer yielded:

tracing type       times            entries recorded
------------      --------          ----------------
irq disabled      43.393            166433066
                  43.282            166172618
                  43.298            166256704

preempt disabled  38.969            159871710
                  38.943            159972935
                  39.325            161056510

Average:

   irqs disabled:  43.324           166287462
preempt disabled:  39.079           160300385

 preempt is 10.8 percent faster than irqs disabled.

I wrote a patch to count function trace recursion and reran hackbench.

With irq disabled: 1,150 times the function tracer did not trace due to
  recursion.
with preempt disabled: 5,117,718 times.

The thousand times with irq disabled could be due to NMIs, or simply a case
where it called a function that was not protected by notrace.

But we also see that a large amount of the trace is lost with the
preempt version.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      b2a866f9
    • S
      ftrace: insert in the ftrace_preempt_disable()/enable() functions · 182e9f5f
      由 Steven Rostedt 提交于 
      Impact: use new, consolidated APIs in ftrace plugins

This patch replaces the schedule safe preempt disable code with the
ftrace_preempt_disable() and ftrace_preempt_enable() safe functions.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      182e9f5f
    • S
      ftrace: introduce ftrace_preempt_disable()/enable() · 8f0a056f
      由 Steven Rostedt 提交于 
      Impact: add new ftrace-plugin internal APIs

Parts of the tracer needs to be careful about schedule recursion.
If the NEED_RESCHED flag is set, a preempt_enable will call schedule.
Inside the schedule function, the NEED_RESCHED flag is cleared.

The problem arises when a trace happens in the schedule function but before
NEED_RESCHED is cleared. The race is as follows:

schedule()
  >> tracer called

    trace_function()
       preempt_disable()
       [ record trace ]
       preempt_enable()  <<- here's the issue.

         [check NEED_RESCHED]
          schedule()
          [ Repeat the above, over and over again ]

The naive approach is simply to use preempt_enable_no_schedule instead.
The problem with that approach is that, although we solve the schedule
recursion issue, we now might lose a preemption check when not in the
schedule function.

  trace_function()
    preempt_disable()
    [ record trace ]
    [Interrupt comes in and sets NEED_RESCHED]
    preempt_enable_no_resched()
    [continue without scheduling]

The way ftrace handles this problem is with the following approach:

	int resched;

	resched = need_resched();
	preempt_disable_notrace();
	[record trace]
	if (resched)
		preempt_enable_no_sched_notrace();
	else
		preempt_enable_notrace();

This may seem like the opposite of what we want. If resched is set
then we call the "no_sched" version??  The reason we do this is because
if NEED_RESCHED is set before we disable preemption, there's two reasons
for that:

  1) we are in an atomic code path
  2) we are already on our way to the schedule function, and maybe even
     in the schedule function, but have yet to clear the flag.

Both the above cases we do not want to schedule.

This solution has already been implemented within the ftrace infrastructure.
But the problem is that it has been implemented several times. This patch
encapsulates this code to two nice functions.

  resched = ftrace_preempt_disable();
  [ record trace]
  ftrace_preempt_enable(resched);

This way the tracers do not need to worry about getting it right.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      8f0a056f
  7. 03 11月, 2008 17 次提交
  9. 02 11月, 2008 7 次提交