[pve-devel] intel pstate: wrong cpu frequency with performance governor

[Alexandre DERUMIER]

>>What is the suggestion - disbale the pstate driver? I think that would increase 
>>power consumption? 

yes, this is increase power consumption. But increase stability & latencies.

my old xeons (previous sandybridge) and amd, always are at maximum cpu frequency.

Redhat have a special daemon "tuned", which have some tunables profiles for this (latency,bandwith, ...)


>>Really? You observed retransmits because of different CPU frequency. I think 
>>retransmits need 
>>much larger speed differences, for example caused by high load (as opposed to 
>>idle nodes). 

I'm seeing a lot less retransmit since I have disable pstate.
(but maybe this is because of bug where frequency was stuck low, and I have also a big cluster with a lot of vms)


----- Mail original -----
De: "dietmar" <dietmar at proxmox.com>
À: "aderumier" <aderumier at odiso.com>, "pve-devel" <pve-devel at pve.proxmox.com>
Envoyé: Mardi 20 Septembre 2016 09:52:51
Objet: Re: [pve-devel] intel pstate: wrong cpu frequency with performance governor

> I think this is the normal behavior of pstate, as they are a lower limit. 
> 
> But for virtualisation, I think it's really bad to have changing frequency. 
> (clock problem for example). 

What is the suggestion - disbale the pstate driver? I think that would increase 
power consumption? 

> Also for corosync, that mean that a loaded node will have faster frequency, 
> and non-loaded node low frequency. 
> This can give us reload corosync.conf after removing a node., because low 
> frequency take more time to get the corosync message than the fastest node 
> https://www.hastexo.com/resources/hints-and-kinks/whats-totem-retransmit-list-all-about-corosync/ 

Really? You observed retransmits because of different CPU frequency. I think 
retransmits need 
much larger speed differences, for example caused by high load (as opposed to 
idle nodes).