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: [email protected]
ReportedBy: [email protected]
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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