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Re: [PATCH v2 0/3] perf/sdt : Support for SDT markers



On 07/18/2014 04:53 PM, Masami Hiramatsu wrote:
Hi Hemant,

(2014/07/17 14:53), Hemant Kumar wrote:
This patchset helps in listing dtrace style markers(SDT) present in user space
applications through perf.
Notes/markers are placed at important places by the
developers. They have a negligible overhead when not enabled.
We can enable them and probe at these places and find some important information
like the arguments' values, etc.
Thanks for your work! This actually helps us a lot :)

Thanks a lot for the appreciation. :)


We have lots of applications which use SDT markers today, like:
Postgresql, MySql, Mozilla, Perl, Python, Java, Ruby, libvirt, QEMU, glib

To add SDT markers into user applications:
We need to have this header sys/sdt.h present.
sys/sdt.h used is version 3.
If not present, install systemtap-sdt-devel package (for fedora-18).

Please refer to the Documentation patch to see how the SDT markers are added into
a program.

With this patchset,
- Use perf to list the markers in the app:
# perf list sdt ./user_app

./user_app :
%user_app:foo_start
%user_app:fun_start

- Also, we can see the SDT markers present in our system in the usual binaries.
These usual binaries are libraries (dsos) listed by ldconfig --print-cache and some
binaries present in PATH environment variable.

First, scan the binaries using :
# perf list sdt --scan
At a glance, maybe we'd better have perf sdt-cache as like as perf buildid-cache
for manage sdt information. what would you think?


I agree with you having perf sdt-cache similar to perf buildid-cache.
But I think if the functionality of perf sdt-cache is only to build the cache, then we can go with the perf list sdt --scan. Since, "perf list sdt" is used for other purposes too, it should be less confusing for the users to just add another option (--scan) to create/modify
the cache. What do you suggest?

Creating a cache of SDT markers...
perf sdt cache created!
  Use : "perf list sdt"
  to see the SDT markers

After the sdt cache file is created, use perf list to view the markers :
# perf list sdt

%rtld : init_start
%rtld : init_complete
%rtld : map_failed
%rtld : map_start
%rtld : lll_futex_wake
...
...
%libgcc : unwind
%libvirt : rpc_server_client_auth_allow
%libvirt : rpc_server_client_auth_fail
%libvirt : rpc_server_client_auth_deny
Looks good :)
It seems very useful for perf users.

Thank you,

Thanks a lot for going through this.

--
Thanks,
Hemant Kumar


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