• 6.8.3 disk activities does not respect isolcpus


    testdasi
    • Minor

    My syslinux boot has:

    isolcpus=32-63

     

    Originally I discovered that when I run btrfs scrub (Main -> diskx -> scrub), it doesn't respect the isolcpus i.e. it uses the cores that are supposed to be isolated (see attached screenshot).

    After a few tries, I also found other activities e.g. copying files between disks (simple cp command on console) also does not respect isolcpus.

    This looks to be system independent as I can reproduce this even on Unraid as a VM.

     

    BTRFS scrub.PNG




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    6 hours ago, efschu said:

    Could you share, what oyu have done?

    Sure. I'm still getting activity on the isolated CPUs when doing a parity check or rebuild, but I can now game on the VM while this is going on without any noticeable hiccups. Right now I'm playing F1 2019 with maxed out graphic settings on a Nvidia 1070 and I lock the FPS to my refresh rate. This is on a AMD Ryzen 3900X. 

     

    Below is my custom edit for my cpu. I suspect there are others that will work, but I've not given it much thought. Once the current bug is out of the beta I'll switch back to pass through and see if that works.

     

      <cpu mode='custom' match='exact' check='full'>
        <model fallback='forbid'>EPYC-IBPB</model>
        <vendor>AMD</vendor>
        <topology sockets='1' dies='1' cores='6' threads='2'/>
        <feature policy='require' name='x2apic'/>
        <feature policy='require' name='tsc-deadline'/>
        <feature policy='require' name='hypervisor'/>
        <feature policy='require' name='tsc_adjust'/>
        <feature policy='require' name='clwb'/>
        <feature policy='require' name='umip'/>
        <feature policy='require' name='stibp'/>
        <feature policy='require' name='arch-capabilities'/>
        <feature policy='require' name='ssbd'/>
        <feature policy='require' name='xsaves'/>
        <feature policy='require' name='cmp_legacy'/>
        <feature policy='require' name='perfctr_core'/>
        <feature policy='require' name='clzero'/>
        <feature policy='require' name='wbnoinvd'/>
        <feature policy='require' name='amd-ssbd'/>
        <feature policy='require' name='virt-ssbd'/>
        <feature policy='require' name='rdctl-no'/>
        <feature policy='require' name='skip-l1dfl-vmentry'/>
        <feature policy='require' name='mds-no'/>
        <feature policy='require' name='pschange-mc-no'/>
        <feature policy='disable' name='monitor'/>
        <feature policy='require' name='topoext'/>
        <feature policy='disable' name='svm'/>
      </cpu>

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    So is this problem going to be ignored? It's not listed in "known issues" or something like that.

     

    I tested the same hardware with Proxmox and I NEVER got random activity on cpus I had isolated to certain vms.

    Link to comment
    2 hours ago, Jeffarese said:

    So is this problem going to be ignored? It's not listed in "known issues" or something like that.

     

    I tested the same hardware with Proxmox and I NEVER got random activity on cpus I had isolated to certain vms.

    My guess is no, as isolcpus is deprecated, and while it does affect users, my guess is the affected user base is pretty small.

    Link to comment

    It's pretty common to isolate cpus to improve performance in VMs, I don't think the user base is that small

    Edited by Jeffarese
    Link to comment

    Running beta 29 as of about an hour ago, so wanted to follow up for anyone still reading this thread. The new beta no longer needs the edits to the XML file to allow proper cpu passthrough to work and with the vm mostly idle I'm seeing about 13% usage in the VM and very similar CPU usage on the unRaid dashboard. 

     

    Also, the unRaid dashboard must be pretty CPU intensive. CPU usage jumps to about 18% on the VM with it open in Chrome :)

     

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