Re: how to get a kernel callgraph starting from a syscall

[Francis Moreau <francis.moro@gmail.com>]

On Fri, Apr 22, 2011 at 7:29 AM, Francis Moreau <francis.moro@gmail.com> wrote:
> On Fri, Apr 22, 2011 at 2:47 AM, David Ahern <dsahern@gmail.com> wrote:
>> On 04/21/11 14:07, Francis Moreau wrote:
>>> On Thu, Apr 21, 2011 at 9:49 PM, David Ahern <dsahern@gmail.com> wrote:
>>>>
>>>> You want the individual samples? if so, perf script dumps them and you
>>>> can see the callchain for each sys_read.
>>>>
>>>
>>> hmm, I don't see what you mean by individual samples.
>>>
>>> I don't think sampling can help in my case (tracing the callchain of
>>> one syscall).
>>>
>>> Could you give me an example of what you have in mind ?
>>>
>>> Thanks
>>
>> I think I get it now. 'perf record' for syscall event stops at sys_read
>> as that is the point the event is generated. You want where the kernel
>> goes starting with sys_read. In that case you are limited to the
>> pre-existing tracepoints (see 'perf list -e tracepoints') to trigger an
>> event and back trace, or if the read causes the processes to block you
>> can you use the context-switch event or sched_switch trace point.
>>
>> You could also insert probe points using perf probe. Lin Ming posted an
>> example of this a couple of weeks ago:
>> # ./perf probe -k ~/vmlinux -s ~/linux-2.6/  find_get_page
>> # ./perf record -e probe:find_get_page -f -g -a
>>
>
> Thanks for you answer.
>
> I think I'll use probe.


Thinking more about it, I think that both solution (probe or
tracepoint) are not adapted.

Because I'm interested in discovering the path taken by the kernel
from a given syscall, therefore I don't know this path. However both
solution imply that the path is known since you need to insert some
'probes' in this path to see it...

-- 
Francis