Issues with @perf directives in systemtap 3.1 on Ubuntu 16.04LTS

Issues with @perf directives in systemtap 3.1 on Ubuntu 16.04LTS

[Geoffrey Blake]

Hi all,

I have been trying to make use of the perf.stp example modified for my
own program I am trying to profile.  I set the perf.hw probes to be
system wide by not supplying a process, but when my other probes
trigger and I read the counters with the @perf() directive, the number
returned for the counters is always the same junk number (it varies
between runs, but never changes during a run).

I am not sure what could be going on.  I have tried the systemtap
package that ships with Ubuntu 16.04LTS and compiled from the tip of
the git repository.  Both versions have the same failure.  Any help
would be appreciated on how to debug this further.

Thanks,
Geoff Blake

Re: Issues with @perf directives in systemtap 3.1 on Ubuntu 16.04LTS

[David Smith]

On 01/23/2017 07:50 AM, Geoffrey Blake wrote:
> Hi all,
> 
> I have been trying to make use of the perf.stp example modified for my
> own program I am trying to profile.  I set the perf.hw probes to be
> system wide by not supplying a process, but when my other probes
> trigger and I read the counters with the @perf() directive, the number
> returned for the counters is always the same junk number (it varies
> between runs, but never changes during a run).
> 
> I am not sure what could be going on.  I have tried the systemtap
> package that ships with Ubuntu 16.04LTS and compiled from the tip of
> the git repository.  Both versions have the same failure.  Any help
> would be appreciated on how to debug this further.

Does the unmodified perf.stp example work on your system? How are you
running your modified example?

-- 
David Smith
dsmith@redhat.com
Red Hat
http://www.redhat.com
256.217.0141 (direct)
256.837.0057 (fax)

Re: Issues with @perf directives in systemtap 3.1 on Ubuntu 16.04LTS

[Geoffrey Blake]

The unmodified perf.stp script is working fine.  The modification I
made was to probe into a library function call by doing:

process("path").library("path").funtion("func") { /* probe code */ }

process("path").library("path").funtion("func").return { /* probe code */ }

This is still yielding the @perf call giving me the same number on
return all the time.
Does @perf not work with library functions?

Thanks,
Geoff Blake

On Mon, Jan 23, 2017 at 9:42 AM, David Smith <dsmith@redhat.com> wrote:
> On 01/23/2017 07:50 AM, Geoffrey Blake wrote:
>> Hi all,
>>
>> I have been trying to make use of the perf.stp example modified for my
>> own program I am trying to profile.  I set the perf.hw probes to be
>> system wide by not supplying a process, but when my other probes
>> trigger and I read the counters with the @perf() directive, the number
>> returned for the counters is always the same junk number (it varies
>> between runs, but never changes during a run).
>>
>> I am not sure what could be going on.  I have tried the systemtap
>> package that ships with Ubuntu 16.04LTS and compiled from the tip of
>> the git repository.  Both versions have the same failure.  Any help
>> would be appreciated on how to debug this further.
>
> Does the unmodified perf.stp example work on your system? How are you
> running your modified example?
>
> --
> David Smith
> dsmith@redhat.com
> Red Hat
> http://www.redhat.com
> 256.217.0141 (direct)
> 256.837.0057 (fax)

Re: Issues with @perf directives in systemtap 3.1 on Ubuntu 16.04LTS

[Stan Cox]

[-- Attachment #1: Type: text/plain, Size: 245 bytes --]


> Does @perf not work with library functions?
The attached perf library example seems to work fine on Fedora.
  ABCDEFGHIJKLMNOPQRSTUVWXYZ
  count 1 min 882141 max 882141
  ABCDEFGHIJKLMNOPQRSTUVWXYZ
  ...
  count 100 min 888775 max 1594700




[-- Attachment #2: tststperf.sh --]
[-- Type: application/x-shellscript, Size: 685 bytes --]