Re: [PATCH][RFC 2/23]: SCST core

[Vladislav Bolkhovitin]

Hi Frédéric,

Frédéric Weisbecker, on 12/20/2008 04:06 PM wrote:
> Hi Vladislav,
>
> 2008/12/18 Vladislav Bolkhovitin <vst@xxxxxxxx>:
> > Frédéric Weisbecker, on 12/14/2008 03:35 AM wrote:
> > > 2008/12/13 Vladislav Bolkhovitin <vst@xxxxxxxx>:
> > > > Also (maybe I simply miss something) looks like ftrace doesn't trace exit
> > > > from functions, only entrance to them. Is it true? Is it possibly to log
> > > > exit from functions as well?
> > > That's true with 2.6.28, the function tracer traces on function entries
> > > only.
> > > But there is an add-on on ftrace which let one to trace on entry and
> > > on return, the function
> > > graph tracer. This tracer uses this facility to output a graph of
> > > function calls and measure
> > > the time elapsed during each function call.
> > > You can also register two custom handlers to do some things you need
> > > on entry and on return.
> > Word "graph" is quite confusing. We don't need any graphs, we need a plain
> > execution path tracing as in the attached example (this is what's currently
> > done).
>
> The word graph is actually here to explain here that we not only trace
> each function call
> but we can actually retrieve all of the call path of a function and
> then draw it as if it was
> C code:
>
>  0) ! 108.528 us  |            }
>  0)               |            irq_exit() {
>  0)               |              do_softirq() {
>  0)               |                __do_softirq() {
>  0)   0.895 us    |                  __local_bh_disable();
>  0)               |                  run_timer_softirq() {
>  0)   0.827 us    |                    hrtimer_run_pending();
>  0)   1.226 us    |                    _spin_lock_irq();
>  0)               |                    _spin_unlock_irq() {
>  0)   6.550 us    |                  }
>  0)   0.924 us    |                  _local_bh_enable();
>  0) + 12.129 us   |                }
>  0) + 13.911 us   |              }
>  0)   0.707 us    |              idle_cpu();
>  0) + 17.009 us   |            }
>  0) ! 137.419 us  |          }
>  0)   <========== |
>  0)   1.045 us    |          }
>  0) ! 148.908 us  |        }
>  0) ! 151.022 us  |      }
>  0) ! 153.022 us  |    }
>  0)   0.963 us    |    journal_mark_dirty();
>  0)   0.925 us    |    __brelse();

Unfortunately, it lacks very useful "TASK-PID, CPU#, TIMESTAMP" header 
fields..

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