linux-kernel - Re: [PATCH] Tracing events with GPIOs

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Date:	Sat, 28 Dec 2013 20:28:45 -0600
From:	Tom Zanussi <tom.zanussi@...el.com>
To:	Jean-Jacques Hiblot <jjhiblot@...phandler.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Tracing events with GPIOs

On Fri, 2013-12-27 at 10:51 -0600, Tom Zanussi wrote:
> On Fri, 2013-12-27 at 15:54 +0100, Jean-Jacques Hiblot wrote:
> > Hi Tom, Steven,
> > 
> > I'm currently doing some tests with the event triggers
> > (git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
> > for-next).
> > At the moment I can't use event triggers with probes dynamically
> > created (with perf probe or via
> > /sys/kernel/debug/tracing/kprobe_events)
> > Predefined probes like
> > /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger are working
> > fine.
> > Am I missing something ?
> > 
> 
> No, it's just that kprobes hasn't been hooked up yet to actually invoke
> the triggers.
> 
> Let me look at doing that over the weekend...
> 

OK, I just posted a patch to add trigger invocations to kprobes, which
you can also find here:

http://git.yoctoproject.org/cgit/cgit.cgi/linux-yocto-contrib/log/?h=tzanussi/kprobes-event-triggers 

I tested it a bit here, but it could use more, so please let me know how
it goes..

Tom


> Tom
> 
> > example:
> > 
> > ----------------------------------------------------------------
> > with a predefined probe
> > ----------------------------------------------------------------
> > 
> > prompt> echo 'stacktrace' >
> > /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
> > prompt> ls
> > prompt> cat /sys/kernel/debug/tracing/trace
> > # tracer: nop
> > #
> > # entries-in-buffer/entries-written: 14/14   #P:1
> > #
> > #                              _-----=> irqs-off
> > #                             / _----=> need-resched
> > #                            | / _---=> hardirq/softirq
> > #                            || / _--=> preempt-depth
> > #                            ||| /     delay
> > #           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
> > #              | |       |   ||||       |         |
> >               ls-971   [000] ....   298.050000: <stack trace>
> >  => ftrace_raw_event_kmem_alloc
> >  => kmem_cache_alloc_trace
> >  => do_execve
> >  => SyS_execve
> >  => ret_fast_syscall
> >               ls-971   [000] ....   298.050000: <stack trace>
> >  => ftrace_raw_event_kmem_alloc
> >  => kmem_cache_alloc_trace
> >  => load_elf_binary
> > [...]
> > 
> > ----------------------------------------------------------------
> > with a dynamically defined probe
> > ----------------------------------------------------------------
> > 
> > prompt> perf probe -a in_kmalloc=__kmalloc
> > prompt> echo 'stacktrace' >
> > /sys/kernel/debug/tracing/events/probe/in_kmalloc/trigger
> > prompt> perf record -e probe:in_kmalloc -aR sleep 10&
> > [... do something here ...]
> > prompt> perf report
> > [...]
> > # Samples: 24  of event 'probe:in_kmalloc'
> > # Event count (approx.): 24
> > #
> > # Overhead  Command      Shared Object         Symbol
> > # ........  .......  .................  .............
> > #
> >     50.00%       ls  [kernel.kallsyms]  [k] __kmalloc
> >     12.50%    sleep  [kernel.kallsyms]  [k] __kmalloc
> >     12.50%       sh  [kernel.kallsyms]  [k] __kmalloc
> >     12.50%     perf  [kernel.kallsyms]  [k] __kmalloc
> >     12.50%     more  [kernel.kallsyms]  [k] __kmalloc
> > [...]
> > 
> > prompt> cat /sys/kernel/debug/tracing/trace
> > # tracer: nop
> > #
> > # entries-in-buffer/entries-written: 0/0   #P:1
> > #
> > #                              _-----=> irqs-off
> > #                             / _----=> need-resched
> > #                            | / _---=> hardirq/softirq
> > #                            || / _--=> preempt-depth
> > #              random: nonblocking pool is initialized
> >               ||| /     delay
> > #           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
> > #              | |       |   ||||       |         |
> 


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