[pve-devel] adding a vm workload scheduler feature

[datanom.net]

Hi all,

On 2015-11-17 08:23, Alexandre DERUMIER wrote:
> 
> 
> What do you think about it ?
> 
Sounds great, but I think memory and io-wait should be part of the list 
as well.

> 
> As we don't have master node, I don't known how to implement this:
> 
> 1) each node try to migrate his own vms to another node with less cpu 
> usage.
>    maybe with a global cluster lock to not have 2 nodes migrating in
> both way at the same time ?
> 
How would you distinguish between operator initiated migration and 
automatic migration?
I should think that operator initiated migration should always overrule 
automatic migration.

> 
> 2) have some kind of master service in the cluster (maybe with
> corosync service ?),
>    which read global stats of all nodes, and through an algorithm, do
> the migrations.
> 
Why not keep it simple? You could extend pvestatd to save the 
performance numbers in a file in a specific folder in /etc/pve since 
pvestatd already has these numbers. Each node names this file by node 
name and if writing the numbers through Data::Dumper then this could be 
a persisted hash like
{
     'cpu' => {
                'cur' => 12,
                'max' => 80
              },
     'mem' => {
                'cur' => 28,
                'max' => 96
              },
     'wait' => {
                 'cur' => 2,
                 'max' => 10
               }
}
cur is the reading from pvestatd and max is the configured threshold on 
each node.

Another daemon on each node on a regular interval assembles a hash 
reading every file in the /etc/pve folder to:
{
    'node1' => {
                 'cpu' => {
                            'cur' => 12,
                            'max' => 80
                          },
                 'mem' => {
                            'cur' => 28,
                            'max' => 96
                          },
                 'wait' => {
                             'cur' => 2,
                             'max' => 10
                           }
               },
     ......
}
and performs decisions according to a well defined algorithm which 
should also take into account that some VM's by configuration can be 
configured to be locked to a specific node.

As for locking I agree that there should be some kind of global locking 
scheme.

Just some quick thoughts.

-- 
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Michael Rasmussen

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