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

[David Ahern <dsahern@gmail.com>]

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

David