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

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Date:	Tue, 30 Dec 2008 20:13:12 +0300
From:	Vladislav Bolkhovitin <vst@...b.net>
To:	Ingo Molnar <mingo@...e.hu>
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

Ingo Molnar, on 12/27/2008 02:20 PM wrote:
> * 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();

This view is OK for us, I can suggest only two things:

1. Add an option to disable "OVERHEAD/DURATION", it isn't needed in our 
case of SCSI commands processing troubleshooting, hence would only hurt 
readability and (I guess) add not needed overhead.

2. If possible, make the view more compact, i.e. with less spaces on 
each line. Our tracing lines can be quite long.

Thanks,
Vlad

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