linux-kernel - Re: [PATCH 1/2] tracing/function-graph-tracer: various fixes and features

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Date:	Wed, 21 Jan 2009 20:43:24 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] tracing/function-graph-tracer: various fixes and
 features


On Wed, 21 Jan 2009, Frederic Weisbecker wrote:

> I thought I would have the time to implement the callbacks in trace_event too but I
> really have to sleep :-(
> That will be for later.

No need to rush. Get to sleep.

> --
> 
> This patch brings various bugfixes:
> 
> _ Drop the first irrelevant task switch on the very beginning of a trace.
>   But actually that only solves the first time one does print the trace file.
>   I have to fix the others cases too.

I'm not sure what you mean by the first time here. Can you explain it
a bit better.

> _ Drop the OVERHEAD word from the headers, the DURATION word is sufficient and will not
>   overlap other columns.
> _ Make the headers fit well their respective columns whatever the selected options.
> 
> Ie, default options:
> 
> # tracer: function_graph
> #
> # CPU  DURATION                  FUNCTION CALLS
> # |     |   |                     |   |   |   |
> 
>  1)   0.646 us    |                    }
>  1)               |                    mem_cgroup_del_lru_list() {
>  1)   0.624 us    |                      lookup_page_cgroup();
>  1)   1.970 us    |                    }
> 
> echo funcgraph-proc > trace_options
> 
> # tracer: function_graph
> #
> # CPU  TASK/PID        DURATION                  FUNCTION CALLS
> # |    |    |           |   |                     |   |   |   |
> 
>  0)   bash-2937    |   0.895 us    |                }
>  0)   bash-2937    |   0.888 us    |                __rcu_read_unlock();
>  0)   bash-2937    |   0.864 us    |                conv_uni_to_pc();
>  0)   bash-2937    |   1.015 us    |                __rcu_read_lock();
> 
> echo nofuncgraph-cpu > trace_options
> echo nofuncgraph-proc > trace_options
> 
> # tracer: function_graph
> #
> #   DURATION                  FUNCTION CALLS
> #    |   |                     |   |   |   |
> 
>   3.752 us    |                  native_pud_val();
>   0.616 us    |                  native_pud_val();
>   0.624 us    |                  native_pmd_val();
> 
> 
> About features, one can now disable the duration (this will hide the overhead too
> for convenient reasons and because on  doesn't need overhead if it hasn't the duration
> 
> echo nofuncgraph-duration > trace_options
> 
> # tracer: function_graph
> #
> #                FUNCTION CALLS
> #                |   |   |   |
> 
>           cap_vm_enough_memory() {
>             __vm_enough_memory() {
>               vm_acct_memory();
>             }
>           }
>         }
> 
> And at last, an option to print the absolute time:
> 
> //Restart from default options
> echo funcgraph-abstime > trace_options
> 
> # tracer: function_graph
> #
> #      TIME       CPU  DURATION                  FUNCTION CALLS
> #       |         |     |   |                     |   |   |   |
> 
>   261.339774 |   1) + 42.823 us   |    }
>   261.339775 |   1)   1.045 us    |    _spin_lock_irq();
>   261.339777 |   1)   0.940 us    |    _spin_lock_irqsave();
>   261.339778 |   1)   0.752 us    |    _spin_unlock_irqrestore();
>   261.339780 |   1)   0.857 us    |    _spin_unlock_irq();
>   261.339782 |   1)               |    flush_to_ldisc() {
>   261.339783 |   1)               |      tty_ldisc_ref() {
>   261.339783 |   1)               |        tty_ldisc_try() {
>   261.339784 |   1)   1.075 us    |          _spin_lock_irqsave();
>   261.339786 |   1)   0.842 us    |          _spin_unlock_irqrestore();
>   261.339788 |   1)   4.211 us    |        }
>   261.339788 |   1)   5.662 us    |      }
> 
> The format is seconds.usecs
> I guess no one needs the nanosec precision here, the main goal is to find when happened
> the events on a cpu when the trace switches from one cpu to another.
> 
> ie:
> 
>   274.874760 |   1)   0.676 us    |      _spin_unlock();
>   274.874762 |   1)   0.609 us    |      native_load_sp0();
>   274.874763 |   1)   0.602 us    |      native_load_tls();
>   274.878739 |   0)   0.722 us    |                  }
>   274.878740 |   0)   0.714 us    |                  native_pmd_val();
>   274.878741 |   0)   0.730 us    |                  native_pmd_val();
> 
> Here there is a 4000 usecs difference when we switch the cpu.

These examples will most likely be cut from the change log. Updating
ftrace.txt would be nice ;-)

> 
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> ---
>  kernel/trace/trace_functions_graph.c |  245 +++++++++++++++++++++-------------
>  1 files changed, 151 insertions(+), 94 deletions(-)
> 

-- Steve

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