[FreeBSD 13] High CPU Usage - rand_harvestq

deltatux

deltatux

Hi all,

Recently I installed a fresh copy of FreeBSD 13 as a KVM guest on my Linux server and was wondering why one of the CPU cores is always pegged at 100%.

When issuing the top -SP command, I see that the rand_harvestq process is consuming 100% of CPU3 on my VM and I'm unsure why, it feels like this could be a bug but not sure.

Here's a screenshot of what I'm seeing:
1621288295030.png


I did some digging and this blogger seems to be experiencing the same problem that I'm facing, the blogger notes that high CPU usage from rand_harvestq happens when the VirtIO RNG is being used. The poster said that this issue was resolved when the "Intel Secure Key RNG" is being used instead. Unfortunately, I don't believe my home server hardware has the Intel Secure Key RNG available.

decomo.info

VirtIO RNG may cause high CPU utilization by rand_harvestq in FreeBSD 13 VM

VirtIO RNG may cause high CPU utilization by rand_harvestq in FreeBSD 13 VM I found my home server suddenly got increased power consumption. Its difference was up to 30W, so it's not obviously error. It was caused by powering up FreeBSD VM on ProxmoxVE, but I had no reasonable reasons. When I...
decomo.info decomo.info

Was wondering if anyone else has run into this issue as well and may have a potential workaround or a bug report is required.

Any suggestions would be much appreciated.

Thank you.
 
kern.random.random_sources='Sony Secure Key RNG' :)
not very random, but light on cpu
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Alain De Vos said:
What's the output of,
Code: 
sysctl kern.random.random_sources
Click to expand...
Thanks for your reply, much appreciated, the output I got was:
kern.random.random_sources: 'VirtIO Entropy Adapter'
Click to expand...

Alain De Vos said:
I found a maybe related bugreport,

230808 – rand_harvestq high CPU utilization

bugs.freebsd.org bugs.freebsd.org
Click to expand...
I'm not sure if it's the same bug but it looks like it might be related. I see that bug was fixed back in 2019, maybe there's a regression for FreeBSD 13? I have another VM on the server that's currently running FreeBSD 12 and doesn't exhibit the same issue. It's rather odd for sure.

EDIT: I think I found a bug report that's for FreeBSD 13.0 for the same issue. The workaround posted seems to suggest to blacklist virtio_random on rc.conf.

254513 – virtio_random: random_harvestq spinning on a CPU with Q35 virtio random device

bugs.freebsd.org bugs.freebsd.org

EDIT2: It looks like the workaround in Bug ID 254513 seems to have worked but I'm not sure what the performance penalty is for disabling virtio_random. Hopefully it'll get fixed soon.

EDIT3: Additional digging seems to suggest that you can't combine the Q35 chipset with the VirtIO RNG Adapter, the combination causes issues. Either remove the VirtIO RNG Adapter from the VM or switch to the I440FX chipset emulation to resolve this issue.
 
roccobaroccoSC said:
* Shutting down does not always work. Sometimes the system just hangs and does not properly shut down.
Click to expand...

Incidentally (not seeking support) this symptom is commonplace with FreeBSD guests in VirtualBox, where EFI is enabled for the guest. Typically: shutdown -p now concludes with the USB-related lines, then I power off the guest.
 
Last edited:
Seems like this bug keeps on being there. I have had the same exact problem under vmware. I am using FreeBSD 12.4-RELEASE-p3 GENERIC right now and when I use a single CPU then this is happening again. When I change the VM to use dual CPUs or more then all is working well.
 
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