From mboxrd@z Thu Jan  1 00:00:00 1970
From: bugzilla-daemon@bugzilla.kernel.org
Subject: [Bug 55061] New: cpu stats reported in cgroup file is erroneous
Date: Sun, 10 Mar 2013 16:14:59 +0000 (UTC)
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https://bugzilla.kernel.org/show_bug.cgi?id=55061

           Summary: cpu stats reported in cgroup file is erroneous
           Product: Virtualization
           Version: unspecified
    Kernel Version: 3.5.3-1.fc17.i686.PAE
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: high
          Priority: P1
         Component: kvm
        AssignedTo: virtualization_kvm@kernel-bugs.osdl.org
        ReportedBy: roopagovind@yahoo.com
        Regression: No


While testing the virsh cpu-stats functionality, I found that the stats
reported in the command output is incorrect, specifically the reported user
time and system time.

Please find a sample output.

virsh cpu-stats fedora-18 --total --start 0 --count 4
CPU0:
    cpu_time            15.321903938 seconds
CPU1:
    cpu_time            11.410812819 seconds
CPU2:
    cpu_time             2.948269295 seconds
CPU3:
    cpu_time             1.724287630 seconds
Total:
    cpu_time            31.405273682 seconds
    user_time            1.310000000 seconds
    system_time         12.860000000 seconds


As you can see here, the user time is less than system_time which is incorrect.
As an experiment, I tried running a while 1 loop inside this guest and observed
that stats for a period of time was not changing appropriately or rather not
the expected way.

While the while 1 loop was running inside the guest, the user_time continued to
be less than system_time which is incorrect. More over the guest is not running
any workload expect this while 1 loop.

So definitely there seems to be a bug in the cgroup accounting of cpu stats.
Please fix this cgroup bug.

I've verified this against different distro versions and flavors and hit the
same issue across all these test environments.

--roopa

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