Re: ERROR: operf_read::convertPerfData

On Sat, 2015-05-30 at 15:23 -0700, Daniel Wilkerson wrote:
> I'm running a vanilla Ubuntu 14.04 install.  I attempted to profile a
> C++ program built using g++.  Other than being multi-threaded and
> using 100G of RAM, it is a pretty normal program.  I assign some
> environment vars and then say "operf" before the program line, like
> this: "VAR=0 operf prog.  My program does not finish and I get the
> error quoted below in appendix A.  I see the recommendation to
> decrease my sampling rate, but is that really the cause of the SIGPIPE
> ?  I must say, this is not a very informative message.
> 
> I attempted to profile a much simpler program on an Ubuntu 14.04
> machine that just did some arithmetic in a loop and
> allocated/deallocated some arrays; no multithreading.  That doesn't
> crash, but opreport just gives a "no samples found" error, quoted
> immediately below.  Does my program stop too fast to be profiled?
> 
> opreport --symbols oprofile_data
> Using /home/dsw/ex_cc/oprofile_data/samples/ for samples directory.
> error: no sample files found: profile specification too strict ?
> make: *** [profile] Error 1
> 
> Daniel
> 

Hi,

in order to narrow the problem a bit, please try:

1) Command `opreport --symbols` without the "oprofile_data" argument.
The "oprofile_data" dir is used by default. If you want to specify some
other dir, you'd need to use the proper option: "--session-dir=dir". By
putting "oprofile_data" there without any switch, opreport thinks, that
"./oprofile_data" is the name of the executed binary. Since there are no
samples of the binary "./oprofile_data", you get the "no samples"
message.


2) Check something about your environment:

* ophelp -r
--> You should see what how oprofile recognizes your HW (or HW support).
It is "Intel Ivy Bridge microarchitecture" in my case.

* perf stat ls
--> You should not get too much of "<not supported>" there:
 Performance counter stats for 'ls':

          0.779068      task-clock (msec)         #    0.003 CPUs utilized          
                 2      context-switches          #    0.003 M/sec                  
                 1      cpu-migrations            #    0.001 M/sec                  
               282      page-faults               #    0.362 M/sec                  
         2,562,134      cycles                    #    3.289 GHz                    
         1,835,655      stalled-cycles-frontend   #   71.65% frontend cycles idle   
   <not supported>      stalled-cycles-backend   
         1,525,423      instructions              #    0.60  insns per cycle        
                                                  #    1.20  stalled cycles per insn
           301,446      branches                  #  386.932 M/sec                  
            12,960      branch-misses             #    4.30% of all branches        

       0.299236997 seconds time elapsed

The "cycles", "branches" and "instructions" should be always supported.
But it depends on your machine's HW as well.

* ocount ls
Event counts (actual) for /usr/bin/ls:
        Event                   Count                    % time counted
        CPU_CLK_UNHALTED        2,201,299                100.00

Ocount counts the event occurences. You can see, that CPU_CLK_UNHALTED event
happened 2.2 million times. If you run the following:

ophelp -d

you'll get something like:

CPU_CLK_UNHALTED:100000:0:1:1

The second value (100000) is the sample rate. It means that when ocount reports
circa 2200k of events, you should get around 2200k/100k = 22 samples.

So even /bin/ls should generate enough samples to be detected by opreport.

* operf ls
* opreport

If the previous things work, try to run `ls` under operf, there should really be
samples.


Hope it helps.
Michael


> 
> ---- appendix A
> 
> ERROR: operf_read::convertPerfData quitting. Bad data read from pipe.
> Closing read end of data pipe. operf-record process will stop with SIGPIPE (13).
> Try lowering the sample frequency to avoid this error; e.g., double the 'count'
> value in your event specification.
> 
> 
>  * * * ATTENTION: The kernel lost 4260291 samples. * * *
> Decrease the sampling rate to eliminate (or reduce) lost samples.
> 
> WARNING: Lost samples detected! See
> /data2/dsw/wyd_runs/runE700/oprofile_data/samples/operf.log for
> details.
> operf-record process killed by signal 13
> Error running profiler
> make[1]: *** [0.align] Error 2
> make[1]: Leaving directory `/data2/dsw/wyd_runs/runE700'
> make: *** [nohup/go1] Error 2
> ^C
> [1]+  Exit 2                  make go
> 
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