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

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Message-ID: <20081227112055.GB18819@elte.hu>
Date:	Sat, 27 Dec 2008 12:20:55 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Vladislav Bolkhovitin <vst@...b.net>
Cc:	Frédéric Weisbecker <fweisbec@...il.com>,
	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>
Subject: Re: [PATCH][RFC 2/23]: SCST core


* Vladislav Bolkhovitin <vst@...b.net> wrote:

>> 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..

those obscure readability in the typical usecases, but you can get them 
anytime via using this existing trace_options runtime switch:

  echo funcgraph-proc > /debug/tracing/trace_options 

resulting in traces like this:

# CPU TASK/PID     OVERHEAD/DURATION            FUNCTION CALLS
# |   |      |              |                   |   |   |   |
 ------------------------------------------
  0) distccd-28400  =>   cc1-30212
 ------------------------------------------

  0)   cc1-30212    |   0.270 us    |    }
  0)   cc1-30212    |               |    __do_fault() {
  0)   cc1-30212    |               |      filemap_fault() {
  0)   cc1-30212    |               |        find_lock_page() {
  0)   cc1-30212    |   0.453 us    |          find_get_page();
  0)   cc1-30212    |   0.997 us    |        }
  0)   cc1-30212    |               |        PageUptodate() {
  0)   cc1-30212    |   0.266 us    |          constant_test_bit();
  0)   cc1-30212    |   0.799 us    |        }
  0)   cc1-30212    |   0.379 us    |        mark_page_accessed();
  0)   cc1-30212    |   3.275 us    |      }
  0)   cc1-30212    |   0.276 us    |      _spin_lock();
  0)   cc1-30212    |   0.389 us    |      page_add_file_rmap();
  0)   cc1-30212    |               |      unlock_page() {
  0)   cc1-30212    |   0.266 us    |        page_waitqueue();
  0)   cc1-30212    |   0.381 us    |        __wake_up_bit();
  0)   cc1-30212    |   1.442 us    |      }
  0)   cc1-30212    |   6.897 us    |    }
  0)   cc1-30212    |+ 11.663 us    |  }
  0)   cc1-30212    |               |  up_read() {
  0)   cc1-30212    |   0.280 us    |    _spin_lock_irqsave();

Thanks,

	Ingo
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