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

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Message-ID: <20081230210303.GB6151@nowhere>
Date:	Tue, 30 Dec 2008 22:03:04 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Vladislav Bolkhovitin <vst@...b.net>
Cc:	Ingo Molnar <mingo@...e.hu>, 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

On Tue, Dec 30, 2008 at 08:13:12PM +0300, Vladislav Bolkhovitin wrote:
> 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.


You can disable the overhead but not yet the duration.
But it's on my TODO list and should be available for 2.6.30


> 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
>

I'm not sure... The spaces are mostly here to keep fixed width columns, 
in case we have huge durations, or long cmdlines...

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