Increase CPU Usage On HV After Upgrade (7.2 -> 7.3)

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Hello ,

After upgrading the system from CentOS 7.2.1511 to CenOS 7.3.1611 I
see that the average processing time has increased from 5-7% to 12-15%
(doubled). Not critical but it is not pleasant. Server as KVM with 5
virtual machines. Someone noticed something similar? If so, how to fix that?

Thx.

14 thoughts on - Increase CPU Usage On HV After Upgrade (7.2 -> 7.3)

  • In the mean time, if you have not disabled it, you should find some collected statistics from sysstat/sar. Look at the sarXX files under /var/log/sa. They should be kept for 30 day by default in CentOS 7. So you can compare cpu, mem, I/O profiles before and after the upgrade. If you have access to Red Hat documents you can look also here:
    https://access.redhat.com/articles/325783

    or in general some articles like this:
    https://www.blackmoreops.com/2014/06/18/sysstat-sar-examples-usage/
    and to create pdf graphics with kSar https://www.thomas-krenn.com/en/wiki/Linux_Performance_Analysis_using_kSar

    HIH, Gianluca

  • Discussed with KVM guys, here’s the answer:
    1% per VM seems to much on idle VM; if the VM is not idle you are getting better performance in exchange. For idle VMs the difference should be roughly 0.1% per VM.

  • Hello Gordon,

    Wednesday, January 18, 2017, 11:52:35 PM, you wrote:

    It is software RAID1 + LVM

    Do not quite understand. What do you mean?

  • Hello Gianluca,

    Wednesday, January 18, 2017, 3:54:15 PM, you wrote:

    Unfortunately, on that host such statistics is disabled.

  • Hello Subscriber,

    Thursday, January 19, 2017, 4:44:04 PM, you wrote:

    But I collect such statistics in Zabbix. And the numbers and graphs indicate an increase in the load on the CPU (ie System time).

  • What at the VMs doing? Are they entirely idle? Are they doing light work, mostly reading from disks? If they’re not generating disk IO, then that’s not related. However, during a recent set of benchmarks, I
    found that disk reads were slower under 7.3 than under 7.2. That might be specific to the system I tested, or it might be related to the change you’re seeing.

  • “load” has another meaning in the context of POSIX system performance counters. I’m pretty sure you’re talking about CPU utilization and not
    “load”, right?

  • Subscriber wrote:

    That’s surprising. That’s such an old, low-level daemon/reporting tool…. Was it disabled deliberately? And why?

    mark

  • Hello Gordon,

    Thursday, January 19, 2017, 4:57:48 PM, you wrote:

    Its gateway from local network to Internet

    At work time – No. Another time in most – Yes

    Well no. They are not loaded the disc(s). No heavy for write operations.

  • Hello Sandro,

    Friday, January 20, 2017, 6:54:02 PM, you wrote:

    kvm_intel

    In CentOS 7.2.1511:

    kernel-3.10.0-327.36.3.el7.x86_64
    qemu-kvm-1.5.3-105.el7_2.7.x86_64
    libvirt-daemon-kvm-1.2.17-13.el7_2.5.x86_64

    After upgrade from 7.2.1511 to 7.3.1611:
    It was (after upgrading to this version, I noticed described in the first report the situation):

    kernel-3.10.0-514.2.2.el7.x86_64
    qemu-kvm-1.5.3-126.el7.x86_64
    libvirt-daemon-kvm-2.0.0-10.el7_3.2.x86_64

    Now (as of 2017/01/22):

    kernel-3.10.0-514.6.1.el7.x86_64
    qemu-kvm-1.5.3-126.el7_3.3.x86_64
    libvirt-daemon-kvm-2.0.0-10.el7_3.4.x86_64

    It takes 1-2 days for monitoring, to determine whether the situation has changed since the last update.

  • It is hard to define that extra % are leak due to upgrade, maybe should try on little heavy load VM and see if it is still constant.

    Xlord

    From: CentOS-virt [mailto:CentOS-virt-bounces@CentOS.org] Hello ,

    After upgrading the system from CentOS 7.2.1511 to CenOS 7.3.1611 I
    see that the average processing time has increased from 5-7% to 12-15%
    (doubled). Not critical but it is not pleasant. Server as KVM with 5
    virtual machines. Someone noticed something similar? If so, how to fix that?

    Discussed with KVM guys, here’s the answer:

    1% per VM seems to much on idle VM; if the VM is not idle you are getting better performance in exchange. For idle VMs the difference should be roughly 0.1% per VM.

    Thx.

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