[pve-devel] [PATCH qemu-server] vm start: set minimum timeout of 300s if using PCI passthrough

[Fiona Ebner]

Am 03.05.23 um 15:37 schrieb Friedrich Weber:
> The default VM startup timeout is max(30, VM memory in GiB) seconds.
> Multiple reports in the forum [0] [1] and the bug tracker [2] suggest
> this is too short when using PCI passthrough with a large amount of VM
> memory, since QEMU needs to map the whole memory during startup (see
> comment #2 in [2]). As a result, VM startup fails with "got timeout".
> 
> To work around this, ensure that the startup timeout is at least 300s
> in case the VM config contains at least one `hostpci[n]` option.
> 
> [0]: https://forum.proxmox.com/threads/83765/post-552071
> [1]: https://forum.proxmox.com/threads/126398/post-552807
> [2]: https://bugzilla.proxmox.com/show_bug.cgi?id=3502
> 
> Signed-off-by: Friedrich Weber <f.weber at proxmox.com>
> ---

Would it make sense to instead add a constant multiplier to the memory
timeout heuristic in presence of PCI passthrough? The user says 65 GiB
takes about 3 min 30 s, so assuming it's more or less linear, the 5 min
from this patch would not be enough for more than ~130 GiB of memory.

> 
> Notes:
>     An alternative workaround is offered by an unapplied patch series [3]
>     of bug #3502 [2] that makes it possible to set VM-specific timeouts
>     (also in the GUI). Users could use this option to manually set a
>     higher timeout for VMs that use PCI passthrough. However, it is not
>     immediately obvious that a higher timeout is necessary. Since the
>     problem seems to come up somewhat frequently, I think it makes sense
>     to have the heuristic choose a higher timeout by default.
>     
>     [2]: https://bugzilla.proxmox.com/show_bug.cgi?id=3502
>     [3]: https://lists.proxmox.com/pipermail/pve-devel/2023-January/055352.html

Yes, I think having both the better heuristic and the configurable
timeout makes sense. Since Daniel left, do you want to have another look
at the series/pick it up?