Post #3057402

2026-05-21 14:44 UTC

@globalc@chaos.social md5sum of /dev/urandom may be asking for a lot of entropy from virt-rng?? I can't think what else it would be doing in qemu - easy enough to find with 'perf' on the host. 'perf kvm' may also be of use; you can trace events in the guest - although I don't think anything more useful. To pass a USB device, I'd use virt-manager to set up the USB passing; easiest way used to be spice but that's possibly gone, but there are other mechanisms; or you could pass serial.

Replies (3)

@penguin42@mastodon.org.uk 2026-05-21 14:45

@globalc@chaos.social IMHO the best solution is a differential case - measure the power without the process, then measure with it.

Open ##3057403
@globalc@chaos.social 2026-05-21 21:04

@penguin42@mastodon.org.uk That's good input - trying with another cpu-bound workload, i.e. stress-ng or a pi-calculator. I'm also heavily using virt-manager, but did not see the needed piece for the usb - it's not really device trough but QEMU acting as host, and serial ontop. True also on the "just switch single applications on/off, compare overall consumption". But can't do on realworld systems providing a service. Also not interacting apache-php processes on same system.

Open ##3057404
@globalc@chaos.social 2026-05-22 08:39

@penguin42@mastodon.org.uk That was it apparently - providing /dev/urandom by itself making more load for the VM. Switching to another load, a pi-calculator, I see the attribution as expected. I'll update the article, and to the least also give that our KVM folks to consume and ask if they are aware. :) Thanks for the idea!

Open ##3057412