title: Accessing performance counters using likwid-perfctr
body: <p>I have been using likwid (<a href="https://github.com/RRZE-HPC/likwid" rel="nofollow noreferrer" title="link">link</a>) for accessing performance counters in my dual socket Intel Xeon E5 2660 v4 processors. I was able to use the tool (<code>likwid-perfctr</code>) successfully until last december. When I got back to the tool today after almost a month, I am getting the following warning:</p>
  
  <p><code>WARN: Counter PMC0 is only available with deactivated HyperThreading. Counter results defaults to 0.
  WARN: Counter PMC1 is only available with deactivated HyperThreading. Counter results defaults to 0.
  WARN: Counter PMC2 is only available with deactivated HyperThreading. Counter results defaults to 0.</code></p>
  
  <p>The problem persists even after enabling/disabling hyperthreading from BIOS. Additionally, I get this error even when I run the perfctr command as root.</p>
  
  <p>Has anybody run into this issue? Was there  any recent kernel update that makes it difficult to read the MSR registers (which could explain the appearance of the warning message in the last month)?</p>
  
  <p>System Information: Debian Stretch, kernel 3.16, likwid version 4.3, and finally the command I am trying to run
  <code>likwid-perfctr -C N:0-27 -g L3CACHE -m executable</code></p>