Re: [RFC PATCH-SERIES cluster/ha-manager/manager/proxmox v3 0/6] clamp load imbalance to unit interval

["Daniel Kral" <d.kral@proxmox.com>]

On Thu Apr 30, 2026 at 1:48 PM CEST, Dominik Rusovac wrote:
> # TL;DR
> clamp load imbalance to value between 0 and 1, and display the value as
> percentage in HA Status panel of PVE UI.
>
> NOTE: This needs a version bump for proxmox-perl-rs, because the changes in
> proxmox-resource-scheduling need to be propagated through those bindings.
>
> # Details
> The currently used load imbalance value is given as the so-called coefficient of
> variation (CV), a value that may exceed 1. As such, the CV value alone lacks
> meaning. A CV value of 0.0 means no imbalance, but what does a value of, say,
> 1.7 mean?
>
> Relative to the number of nodes in a cluster, it is possible to determine the
> upper bound of the CV value [0][1]. By dividing the CV value by its upper
> bound, the load imbalance can be represented as a value that varies between 0
> and 1. Expressing the CV as a percentage makes the concept of load imbalance
> easier to interpret.
>
> # Summary of Changes
> This series:
> - represents load imbalance as a value between 0 and 1;
> - adds a maximum value of 1.0 for load scheduler options; and
> - integrates the load imbalance value within the HA status endpoint;
>   this is to provide feedback on the prevailing load imbalance in the PVE UI.
>
> # Refs
> [0] https://repositorio.ipbeja.pt/server/api/core/bitstreams/8ed9a444-dbe0-402f-9d2f-90c5bf6e418c/content
> [1] https://stats.stackexchange.com/questions/18621/maximum-value-of-coefficient-of-variation-for-bounded-data-set

I'm running this patch series on my 3-node test cluster. I tested this
by inducing a few imbalance spikes for a couple of rounds with some
build jobs running and letting the cluster stay mostly idle for a while.

Works good for me so far, which is to be expected since this should only
be a mapping to the unit interval. It's also very helpful to be able to
look at the most recent load imbalance, thanks for the series!

Besides the two small nits, I wonder if we should change the default
imbalance threshold value of 0.3 as with these patches applied the
behavior of the load balancer changes and makes the trigger more
insensitive by default.

For example, for the smaller cluster sizes:

    >>> [(0.3/math.sqrt(n-1), math.sqrt(n-1)) for n in range(2,10)]
    [
        (2, 0.3, 1.0),
        (3, 0.21213203435596423, 1.4142135623730951),
        (4, 0.17320508075688773, 1.7320508075688772),
        (5, 0.15, 2.0),
        (6, 0.13416407864998736, 2.23606797749979),
        (7, 0.12247448713915891, 2.449489742783178),
        (8, 0.11338934190276816, 2.6457513110645907),
        (9, 0.10606601717798211, 2.8284271247461903)
    ]

Though this could be done as a follow-up to this series.

Otherwise, consider the patches (with the nits resolved) as:

Reviewed-by: Daniel Kral <d.kral@proxmox.com>
Tested-by: Daniel Kral <d.kral@proxmox.com>