linux-kernel - Re: [PATCH][RFC 2/23]: SCST core

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Date:	Tue, 23 Dec 2008 22:11:48 +0300
From:	Vladislav Bolkhovitin <vst@...b.net>
To:	Frédéric Weisbecker <fweisbec@...il.com>
CC:	Steven Rostedt <srostedt@...hat.com>,
	Sam Ravnborg <sam@...nborg.org>, linux-scsi@...r.kernel.org,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	Mike Christie <michaelc@...wisc.edu>,
	Jeff Garzik <jeff@...zik.org>,
	Boaz Harrosh <bharrosh@...asas.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, scst-devel@...ts.sourceforge.net,
	Bart Van Assche <bart.vanassche@...il.com>,
	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH][RFC 2/23]: SCST core

Hi Frédéric,

Frédéric Weisbecker, on 12/20/2008 04:06 PM wrote:
> Hi Vladislav,
> 
> 2008/12/18 Vladislav Bolkhovitin <vst@...b.net>:
>> Frédéric Weisbecker, on 12/14/2008 03:35 AM wrote:
>>> 2008/12/13 Vladislav Bolkhovitin <vst@...b.net>:
>>>> 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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