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Devator
Asked: 2011-12-02 12:58:04 +0800 CST

Domain-0 high CPU load

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My Xen HVM machine has 4 cores on 2.4 Ghz however top gives me a load of 2-3. There are running 20 VM's on it (most of them are idle). The HDD is also almost idle (200 KB/s write and 6 KB/s read).

xentop gives me Domain-0 -----r 223766 121.0 4376576 26.1 no limit n/a 4 25 6105332 2824789 0 0 0 0 0 (so 121.0 as CPU% usage).

What's the reason of this? None of the VPSs have high CPU usage. It can't be the IO.

Anyone with some more experience know how to pinpoint this problem?

Thanks in advance.

Edit: You can find the output of top here: http://dl.dropbox.com/u/6166898/top.txt And here's the xentop full output: http://dl.dropbox.com/u/6166898/xentop.txt

There are some Windows VM's on it, I'm using Xen in conjunction with SolusVM.

virtualization xen linux

3 Answers

  1. Best Answer

    The high CPU load has been fixed by updating to Xen kernel 3.4.3 (from kernel 3.1.2).

    Thanks to those who tried to help me!

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  2. Your Windows VMs are probably the root cause of your high CPU load.

    Open-source Xen doesn't provide drivers for Windows PV (at least not officially... I guess you could try those Open Source Windows PV drivers for Xen or take a look at this blog post on how to install Windows 2k8 R2 + the GPVPV drivers - the information there could help you). Btw what versions of Windows are you running on your Windows VMs?

    One thing you can try though is go into every Windows VM's Device Manager and change the HAL to ACPI Multi and force reboot.

    Finally please post the output of ps fawwux to see a list of processes and work out what's using the CPU utilization.

    PS: If you want to provide Windows VPS with Xen, use XenServer Express (free) or Enterprise ($$) and use the bundled PV drivers.

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  3. Perhaps this is massively wrong, but given that you've got 4 cores, and the load average is a measure of number of processes waiting for CPU time, perhaps there's actually no problem.

    Have a read of Understanding Load Averages, I suspect that there's not actually any major problem.

    You haven't mentioned whether the server or it's VMs are misbehaving, or if it's just that the load average is higher than you'd expect. If it's just the latter, you might want to review and readjust your expectations.

    From the vmstat output, the host looks happy, the IOWait is low, the load average is less than the number of cores. You might want to fiddle with CPU affinities, but I'd say that it's probably actually performing OK, from the information you've provided.

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