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, set a larger default timeout if at least one PCI device is passed through. The question remains how to choose an appropriate timeout. Users reported the following startup times: ref | RAM | time | ratio (s/GiB) --------------------------------- [1] | 60G | 135s | 2.25 [1] | 70G | 157s | 2.24 [1] | 80G | 277s | 3.46 [2] | 65G | 213s | 3.28 [2] | 96G | >290s | >3.02 The data does not really indicate any simple (e.g. linear) relationship between RAM and startup time (even data from the same source). However, to keep the heuristic simple, assume linear growth and multiply the default timeout by 4 if at least one `hostpci[n]` option is present, obtaining `4 * max(30, VM memory in GiB)`. This covers all cases above, and should still leave some headroom. [0]: https://forum.proxmox.com/threads/83765/post-552071 [1]: https://forum.proxmox.com/threads/126398/post-592826 [2]: https://bugzilla.proxmox.com/show_bug.cgi?id=3502 Suggested-by: Fiona Ebner <f.eb...@proxmox.com> Signed-off-by: Friedrich Weber <f.we...@proxmox.com> --- Notes: changes since v1 (was called "vm start: set minimum timeout of 300s if using PCI passthrough", 20230503133723.165739-1-f.we...@proxmox.com): * Use a constant multiplier as suggested by Fiona (thx!) Another 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 when using PCI passthrough. Since the problem seems to come up somewhat frequently, I think it makes sense to have the heuristic choose a higher timeout by default. As discussed in v1, I'll also pick up the patch series to allow users to set custom timeouts [3], also to offer a workaround for cases where the new heuristic chooses a timeout that is still too short. [2]: https://bugzilla.proxmox.com/show_bug.cgi?id=3502 [3]: https://lists.proxmox.com/pipermail/pve-devel/2023-January/055352.html PVE/QemuServer/Helpers.pm | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/PVE/QemuServer/Helpers.pm b/PVE/QemuServer/Helpers.pm index 8817427..0afb631 100644 --- a/PVE/QemuServer/Helpers.pm +++ b/PVE/QemuServer/Helpers.pm @@ -152,6 +152,13 @@ sub config_aware_timeout { $timeout = int($memory/1024); } + # When using PCI passthrough, users reported much higher startup times, + # growing with the amount of memory configured. Constant factor chosen + # based on user reports. + if (grep(/^hostpci[0-9]+$/, keys %$config)) { + $timeout *= 4; + } + if ($is_suspended && $timeout < 300) { $timeout = 300; } -- 2.39.2 _______________________________________________ pve-devel mailing list pve-devel@lists.proxmox.com https://lists.proxmox.com/cgi-bin/mailman/listinfo/pve-devel
