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From: "dsmith at redhat dot com" <sourceware-bugzilla@sourceware.org>
To: systemtap@sourceware.org
Subject: [Bug testsuite/17155] New: systemtap.examples/profiling/functioncallcount.stp failures on x86_64
Date: Mon, 14 Jul 2014 13:54:00 -0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=17155

            Bug ID: 17155
           Summary: systemtap.examples/profiling/functioncallcount.stp
                    failures on x86_64
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: testsuite
          Assignee: systemtap at sourceware dot org
          Reporter: dsmith at redhat dot com

When I run the systemtap.examples/check.exp testcase (which tests all the
examples), the functioncallcount.stp example fails about half the time on
x86_64. When it fails, I see this in systemtap.log:

====
ERROR: probe overhead exceeded threshold
WARNING: Number of errors: 1, skipped probes: 0
WARNING: /usr/local/bin/staprun exited with status: 1
Pass 5: run failed.  [man error::pass5]
child process exited abnormally
RC 1
FAIL: systemtap.examples/profiling/functioncallcount run
====

The guts of functioncallcount.stp look like:

====
probe kernel.function(@1).call {  # probe functions listed on commandline
  called[probefunc()] <<< 1  # add a count efficiently
}

global called

probe end {
  foreach (fn in called-)  # Sort by call count (in decreasing order)
  #       (fn+ in called)  # Sort by function name
    printf("%s %d\n", fn, @count(called[fn]))
  exit()
}
====

Because of bug #13693, probefunc() was rewritten and now has a higher overhead.
If we switch to ppfunc(), this example script should work more often.

(The use of the new probefunc() may also be contributing to bug #17140)

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