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

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

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.

Maybe it would be nice to have ftrace integrated in perf ?

Thanks
-- 
Francis