erplibre/LongTest

LongTest — tests that create real machines

These are not unit tests. They create virtual machines, install systems on them, and take hours. They live here and not in test/, which the unit runner sweeps: ./script/test/run_unit_test.sh must stay runnable in seconds on any machine, including one without virtualisation.

Run them from the menu — TODO › Execute › Test › Long tests — or directly.

deep_proxmox.py — how deep does Proxmox-in-Proxmox go?

The practicable nesting depth cannot be deduced, only measured — and one measurement is not a measurement.

A manual look at one fourth-level VM found a guest 36 times slower than real time (583 seconds of wall clock for 16 seconds of guest time, each ACPI line taking a second) and then a frozen kernel: identical RIP across three samples two minutes apart, and not one byte written to disk.

Running this script refuted the conclusion drawn from it. Its own fourth-level VM — 2 vCPU where the manual one had 12 — booted, installed, and wrote gigabytes. What looked like a nesting ceiling was a parallelism ceiling under nesting. That is exactly what the algorithm caps, and this is how it stopped being a guess.

Which is the point of the script: a number obtained once, on one machine, in one chain, is an anecdote.

./LongTest/deep_proxmox.py                        # three levels, ~30 minutes
./LongTest/deep_proxmox.py --dry-run              # the plan, nothing created
./LongTest/deep_proxmox.py --depth 5              # ask for more, knowingly
./LongTest/deep_proxmox.py --detruire             # undo it

How deep is worth asking for

The depth is the only setting, and three is the default because three works. Measured on a 28-core machine, one full descent per row:

level	boot (ssh)	install	total
1	0 s	200 s	280 s
2	37 s	344 s	495 s
3	93 s	777 s	1 064 s
4	15 608 s	26 306 s	did not finish

Three levels cost half an hour. The fourth cost 4 h 20 of boot and 7 h 18 of install on the same machine — everything there is 15 to 30 times slower, not just one step. And it lands exactly where the hardware vendors stop: level 4 is the third nested hypervisor, and AMD documents two.

A wider guest makes it worse, sharply: at level 4, one extra vCPU multiplied the boot by 9.4 (1 664 s at two vCPU, 15 608 s at three), and at eight vCPU the guest read 32 MiB in 106 minutes with a static instruction pointer. At levels 2 and 3 that same vCPU costs nothing.

So: three by default, five if you want to know, ten only to watch the wall.

The descent is uniform. Every level, the first included, goes through the same six steps: create, wait for ssh, install Proxmox, reboot and check the kernel, bring pmxcfs back up, check the storage. Only creation differs — libvirt locally, qm afterwards.

It sends our install_proxmox.sh over scp instead of letting the VM clone the repository: it is our code we want to exercise, and the remote is often behind the checkout — a fix absent from the remote made the same defect "come back" on three VMs in a row.

The resource algorithm — sized from the bottom up

The first version handed down whatever the parent could spare, and a real descent showed what that costs. Level 4 ended up with 44 GB of memory and 2 vCPU on a host that had 2 — a hundred percent overcommit, at every level, with the hypervisor itself to serve on top. Its install ran past two and a half hours against thirteen minutes for level 3, and extrapolating that ratio gave five years for the tenth.

So the direction is reversed for memory and disk. The deepest level gets what a test Proxmox actually asks for — 4 GB of memory, 25 GB of disk — and every parent above it adds its own overhead and nothing else: 2 GiB and 10 GB. A ten-level descent therefore asks its first level for 22 GB and 115 GB, where handing resources down wanted 50 GB of memory for the same depth. The processor follows a different rule; see below.

Three budgets can bound the depth, and script/proxmox/nesting.py names the one that ran out:

• memory — every level must run its own daemons (pve-cluster, pvestatd, pvedaemon, pveproxy) and hold its child;
• disk — the child's disk lives inside the parent's, which must also hold its own system;
• processor — it does not grow with depth. Every nested level keeps a fixed, narrow width; only the first level counts against the physical cores. Either the machine can carry that first level or it can carry nothing.

That third rule is measured, and it cost two descents to get right. A nested guest at the fourth level freezes in early boot as soon as it is wide: twelve vCPU the first time, eight the second — same instruction pointer at three readings five minutes apart, 32 MiB read and not one byte more for 106 minutes. Two vCPU boots.

The first freeze was blamed on overcommit: that VM had twelve vCPU on a host with two. The second measurement refuted it — eight vCPU on a parent with nine, load 1.47, no overcommit at all, and the same freeze. It is the nested guest's vCPU count, not its ratio to its host's.

At the third level, 9 vCPU boots in 117 s. The threshold sits between the third and fourth level, so no nested level is ever made wide. An earlier version of this algorithm gave each parent one vCPU more than its child, which made level 4 eight wide — exactly the frozen case. The rule made wide what must stay narrow.

Hence three fixed widths: VCPU_METAL for level 1 (on bare metal, no freeze risk — eleven vCPU booted there in 42 s), VCPU_IMBRIQUE for the deepest, and VCPU_INTERMEDIAIRE in between, wide enough to host its child without being as narrow as it. That middle number is a hypothesis: two is proven to boot at the fourth level and eight is proven to freeze, with nothing measured in between. The descent decides.

Memory is not the lever. On that same manual VM, dropping it from 9 GB to 2 GB moved nothing — it stopped after reading the same 32 MiB, which is simply the size of the boot files.

The plan is printed before anything is created, and the script never promises a depth it knows will not fit — better to announce six levels and reach six than to promise ten and die at the seventh without knowing why.