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Thread: VirtualBox huge performance regression after update host to 20.04

  1. #11
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    Re: VirtualBox huge performance regression after update host to 20.04

    Hmm. I too have 16 GB physical RAM, same as the author of that blog entry.

    I sometimes do run a couple VMs concurrently, and haven't noticed any problems at all with that and host I/O cache. Then again, I don't do heavy loads with multiple VMs running, and I did temporarily reduce the RAM of at least one VM.

    Ah, key word in that quote is "immensely". So far that has not been my experience at all. I think I will backup my system and then just try some heavy loads and report back. Thanks!

  2. #12
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    Re: VirtualBox huge performance regression after update host to 20.04

    Just tested some heavy loads with host I/O cache enabled. That lot drove host swap usage up to only 26 MB. And the host had only one or two minor performance glitches over a few hours of heavy load. So I think I should be good to use host I/O cache

    (With numbers like that, I would wonder if reducing the amount of RAM of the VM by up to 512 MB would completely avoid swap usage? Is it worth trying?)

    Unfortunately I'm not sure if the heavy loads might still have performance regression compared to under 18.04 host. Like approximately an extra 10 minutes on workloads that under 18.04 host lasted 1-2 hours. Now I did update that guest since using it under 18.04 host. And I was intentionally pushing things in a way I know can slow this down, but I don't recall it being that significant?
    Last edited by halogen2; June 24th, 2020 at 02:50 AM.

  3. #13
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    Re: VirtualBox huge performance regression after update host to 20.04

    I did try reducing the VM's RAM slightly. It significantly reduced swap usage. And it improved performance of the heavy load. Still not as good as it was under 18.04 host, but I got close. I think my VMs might just be slightly over-provisioned for using host I/O cache.

  4. #14
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    Re: VirtualBox huge performance regression after update host to 20.04

    Quote Originally Posted by halogen2 View Post
    I did try reducing the VM's RAM slightly. It significantly reduced swap usage. And it improved performance of the heavy load. Still not as good as it was under 18.04 host, but I got close. I think my VMs might just be slightly over-provisioned for using host I/O cache.
    Interesting thought!
    I the past I have always provisioned my VMs with as much RAM as I could from the host, ie 4G from the host's 8G, but perhaps reducing it to 3G or 3.5G is worth a try.

    I am not seeing any real problems now, though, with the host I/O cache enabled, as I don't use the VMs for any heavy load work; they are simply to test different DE versions of 20.04 or totally different distros
    DISTRO: Xubuntu 20.04-64bit --- Code-tags --- Boot-Repair --- Grub2 wiki & Grub2 Basics --- RootSudo --- Wireless-Info --- SolvedThreads

  5. #15
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    Re: VirtualBox huge performance regression after update host to 20.04

    I reduced the RAM of my VMs that had 4G to 3G RAM and I am pleasantly surprised that it seems to make them all run smoother and quicker, particularly an Arcolinux-Xfce VM which suddenly is now booting to a full xfce4 GUI in about 10 seconds, much faster than before.

    This has certainly made me rethink the resources that I set for any VMs in future!
    DISTRO: Xubuntu 20.04-64bit --- Code-tags --- Boot-Repair --- Grub2 wiki & Grub2 Basics --- RootSudo --- Wireless-Info --- SolvedThreads

  6. #16
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    Re: VirtualBox huge performance regression after update host to 20.04

    ... and solved.

    To sum up:

    1) Enable "Use host I/O cache" for the SATA controller with the VM's hard disk(s).

    2) Then, if the VM inevitably causes the host to use swap, reduce the RAM of the VM. Reduce at least to the point the host seems not to need swap, and possibly some beyond that. I reduced mine to 6 GB (6144 MB). There seems to be something special about that number I don't understand. Even small deviations in either direction result in measurably worse performance on heavy loads

    Anyway, with these changes my VirtualBox VMs performance is slightly better than before under 18.04 host.

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