Time accounting for KVM guests running mixed IO and CPU workloads seems wrong.
KVM host: CentOS 6, x86_64, Linux 3.14.33 KVM guest: CentOS 6, x86_64, Linux 3.14.33, one vCPU. Both guest and host enabled CONFIG_IRQ_TIME_ACCOUNTING and CONFIG_PARAVIRT_TIME_ACCOUNTING The KVM guest was running iperf network workload and a CPU-bound loop workload. On the host, the KVM guest and four while(1) loops were consolidated to one physical CPU. Top command in the host showed 20% CPU utilization for the KVM guest and each loop process. However, the time accounting was apparently wrong as the iperf performance in the KVM guest was just slightly lower than its peak throughput when it ran on a dedicated physical CPU. I expected the throughput to be "proportional" or at least much lower than its peak as only 20% CPU was allocated to the KVM guest. The performance of co-running loops did see significant drops. The KVM guest and loops were put in the same cgroup with same shares. The problem seems to be that the IO process inside the KVM guest silently eats up CPU cycles that are accounted to CPU-bound processes outside of the KVM guest. This seems to be a serious fairness or security concern between consolidated workloads. Thanks, Yun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
