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

Frederic Weisbecker
2008-12-30T21:03:22Z

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@vlnb.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...