[Bug runtime/15912] New: on rawhide, we're getting perf probe read errors

[Bug runtime/15912] New: on rawhide, we're getting perf probe read errors

[dsmith at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=15912

            Bug ID: 15912
           Summary: on rawhide, we're getting perf probe read errors
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: runtime
          Assignee: systemtap at sourceware dot org
          Reporter: dsmith at redhat dot com

On rawhide (3.11.0-0.rc6.git4.1.fc21.x86_64), although the perf.exp testcase
passes, the log file shows several errors, like 'ERROR: _stp_perf_read':

====
spawn /usr/local/bin/stap -c towers.x -e
        global towers
        global main

        probe perf.hw.instructions.process("towers.x").counter("a")
        {
            counter_a += 1
        }

        probe perf.hw.instructions.process("towers.x").counter("b")
        {
            counter_b += 1
        }
        probe process("towers.x").statement("towers@towers.c")
        {
            towers <<< @perf("a")
        }

        probe process("towers.x").statement("main@towers.c")
        {
            main <<< @perf("b")
        }

        probe end
        {
            printf("count main=%d\ncount towers=%d\ncounter %d/%d\n",
                   @count(main), @count(towers), counter_a, counter_b)
            printf("min main=%d\nmin towers=%d\n", @min(main),
                   @min(towers))
            printf("max main=%d\nmax towers=%d\n", @max(main),
                   @max(towers))
        }
WARNING: Statements in perf counter probe will never be reached.: operator '{'
at /usr/local/share/systemtap/tapset/linux/perf.stp:12:60^M
 source: probe perf.hw.instructions        = perf.type(0).config(1) { }
                                                                    ^
WARNING: never-assigned local variable 'counter_a' (alternatives: counter_b
towers main): identifier 'counter_a' at <input>:28:36
 source:                   @count(main), @count(towers), counter_a, counter_b)
                                                         ^
WARNING: never-assigned local variable 'counter_b' (alternatives: counter_a
towers main): identifier 'counter_b' at :28:47
 source:                   @count(main), @count(towers), counter_a, counter_b)
                                                                    ^
WARNING: perf probe
'perf.type(0).config(1).sample(0).process("towers.x").counter("b")' is not
supported by this kernel (-2).
WARNING: perf probe
'perf.type(0).config(1).sample(0).process("towers.x").counter("a")' is not
supported by this kernel (-2).
ERROR: _stp_perf_read
ERROR: _stp_perf_read
ERROR: _stp_perf_read
ERROR: _stp_perf_read
ERROR: _stp_perf_read
ERROR: _stp_perf_read
ERROR: _stp_perf_read
ERROR: _stp_perf_read
ERROR: _stp_perf_read
ERROR: _stp_perf_read
ERROR: _stp_perf_read
ERROR: _stp_perf_read
count main=1
count towers=19
counter 0/0
min main=0
min towers=0
max main=0
max towers=0
ERROR: _stp_perf_read
ERROR: _stp_perf_read
ERROR: _stp_perf_read
ERROR: _stp_perf_read
ERROR: _stp_perf_read
ERROR: _stp_perf_read
ERROR: _stp_perf_read
ERROR: _stp_perf_read
WARNING: /usr/local/bin/staprun exited with status: 1
Pass 5: run failed.  [man error::pass5]
====

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[Bug runtime/15912] on rawhide, we're getting perf probe read errors

[dsmith at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=15912

--- Comment #1 from David Smith <dsmith at redhat dot com> ---
Created attachment 7177
  --> https://sourceware.org/bugzilla/attachment.cgi?id=7177&action=edit
full systemtap.log

Here's the full systemtap.log from that test run.

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[Bug runtime/15912] on rawhide, we're getting perf probe read errors

[dsmith at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=15912

David Smith <dsmith at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |INVALID

--- Comment #2 from David Smith <dsmith at redhat dot com> ---
From some further investigation, it looks like these errors are expected. Those
error messages are output since those hw perf counter probes don't work on this
virtual machine.

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[Bug runtime/15912] on rawhide, we're getting perf probe read errors

[wcohen at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=15912

William Cohen <wcohen at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |wcohen at redhat dot com

--- Comment #3 from William Cohen <wcohen at redhat dot com> ---
RHEL6 machines don't seem to make the performance counters available to guests.
 However, for newer versions of Fedora running as the host it is possible to
use the performance counters in a guest. When the guest VM is shutdown in
libvirt. View->Details for the guest VM.  On the details Select Processor, then
hit the "Copy host CPU configuration".  Then you can start up the guest VM.

So for a RHEL6 guest on a F19 host:


$ perf stat ls

 Performance counter stats for 'ls':

          0.680177 task-clock                #    0.728 CPUs utilized          
                 0 context-switches          #    0.000 K/sec                  
                 0 cpu-migrations            #    0.000 K/sec                  
               242 page-faults               #    0.356 M/sec                  
         1,138,470 cycles                    #    1.674 GHz                    
         1,334,983 stalled-cycles-frontend   #  117.26% frontend cycles idle   
         1,162,180 stalled-cycles-backend    #  102.08% backend  cycles idle   
           932,252 instructions              #    0.82  insns per cycle        
                                             #    1.43  stalled cycles per insn
           189,550 branches                  #  278.677 M/sec                  
            10,156 branch-misses             #    5.36% of all branches        
[37.47%]

       0.000933886 seconds time elapsed

However, the numbers do look a bit off for stalled-cycles-frontend and
stalled-cycles-backend.

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