Re: [pve-devel] [PATCH ha-manager v2 02/26] manager: improve signature of select_service_node

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

On 6/23/25 18:21, Thomas Lamprecht wrote:
> Am 20.06.25 um 16:31 schrieb Daniel Kral:
>> +=head3 select_service_node(...)
>> +
>> +=head3 select_service_node($groups, $online_node_usage, $sid, $service_conf, $sd, $mode)
>> +
>> +Used to select the best fitting node for the service C<$sid>, with the
>> +configuration C<$service_conf> and state C<$sd>, according to the groups defined
>> +in C<$groups>, available node utilization in C<$online_node_usage>, and the
>> +given C<$mode>.
>> +
>> +The C<$mode> can be set to:
>> +
>> +=over
>> +
>> +=item C<'none'>
>> +
>> +Try to stay on the current node as much as possible.
> 
> Why use "none" then? "no mode" is not really helping understand
> what happens. Maybe it can be resolved with better names/descriptions,
> even for the parameter name (like maybe "node_preference"?), but another
> option might be to combine the flags into a hash ref $opts parameter, as
> that would also avoid the issues of rather opaque "1" or "0" params on
> the call sites, not saying it's a must, but we use that pattern a few
> times and conflating such flags into a single string param comes with
> its own can of worms (bit more about that below).

I thought about putting them in an $opts, but I felt like a enum-like 
type would fit here better to reduce the amount of states slightly as 
setting $try_next more or less already implied $best_scored (not the 
other way around). $mode = 'none' is really no good information here, I 
think $node_preference will be a better name for it here.

> 
>> +
>> +=item C<'best-score'>
>> +
>> +Try to select the best-scored node.
>> +
>> +=item C<'try-next'>
> 
> Not sure if switching to a free form string that is nowhere checked for
> unknown (invalid) values really is an improvement over the status quo.
> Rejecting unknown modes upfront should be definitively added.
> 
> Also can we please move the item description as short sentence after the
> `=item ...`, i.e., on the same line, to reduce bloating up the code too
> much with POD.
> 
> =item C<'none'>: Try to stay on the current node as much as possible.
> =item C<'best-score'>: Try to select the best-scored node.
> =item C<'try-next'>: ...?

Will definitely do that!

Speaking of 'try-next' (more below), shouldn't $sd->{failed_nodes}->@* 
be cleaned as soon as the service was successfully started on a node? I 
feel like $try_next was introduced to separate it from the 'stay on 
current node as much ass possible' behavior and might not be needed 
anymore now with an explicit $node_preference = 'none'? Then we're only 
left with $node_preference = 'none' / 'best-score' (where the latter is 
the standard behavior of the helper.

> 
> 
>> +
>> +Try to select the best-scored node, which is not in C<< $sd->{failed_nodes} >>,
>> +while trying to stay on the current node.
> 
> might be a bit to long since I did more in the HA stack, but is "while trying
> to stay on the current node" correct?


Right, I misread the last part at select_service_node(...)

     my $found;
     for (my $i = scalar(@nodes) - 1; $i >= 0; $i--) {
         my $node = $nodes[$i];
         if ($node eq $current_node) {
             $found = $i;
         }
     }

     if ($mode eq 'try-next') {
         if (defined($found) && ($found < (scalar(@nodes) - 1))) {
             return $nodes[$found + 1];
         } else {
             return $nodes[0];
         }
     } else {
         return $nodes[0];
     }

for preferring the $current_node there but it actually is the next-best 
node after $current_node after sorting the nodes by the Usage's scores. 
If 'try-next' is set, shouldn't $current_node already have been deleted 
from $pri_nodes/@nodes here by

     if ($mode eq 'try-next') {
         foreach my $node (@$tried_nodes) {
             delete $pri_nodes->{$node};
         }
     }

Either way, the last part of the description is wrong and I'll remove it.


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