5.3 Merge window, part 2

Posted Jul 22, 2019 19:25 UTC (Mon) by Cyberax (✭ supporter ✭, #52523)
In reply to: 5.3 Merge window, part 2 by mtaht
Parent article: 5.3 Merge window, part 2

Yes, this is super-nice.

You can also do that with VirtualBox (by specifying the "warp factor" via --warp-pct) but I'm not aware of any other virtualization environment that can do this.

5.3 Merge window, part 2

Posted Jul 23, 2019 20:13 UTC (Tue) by johill (subscriber, #25196) [Link]

I looked in qemu, and it sort of has this - if you emulate fully instead of using kvm, which is not feasible.

I think it *could* be done in qemu, remove the TSC, simulate an HPET that has the desired properties and use a virt-aware guest to do the idle handling? But it's tricky and probably requires touching not only qemu and the guest kernel, but quite possibly also the host kernel. Though then I wonder how virtualbox does it, maybe I should look at that.

Anyway, UML is good for me and actually simplifies my use case, so that's it for now. Seeing how much interest this has garnered, maybe somebody else will pick it up elsewhere :-)

Btw, I broke it in a build fix at the last minute, so you need https://patchwork.ozlabs.org/patch/1134739/ to actually use it.

For wifi tests in wpa_s/hostapd it cut down the time required from ~45m to ~7m on my machine, but I run with more kernel debug options now (which wasn't even possible before) in ~10m.

Next up is to add vhost-user support to UML (WIP) and then add a virtio-clock/idle driver to UML that uses it, so I can run multiple things (or instances of UML machines) on the same virtual time...