are CT cores pinned during runtime or can switch between E and P cores ?

tomtom13

Well-Known Member
Dec 28, 2016
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Hi,

I was researching intel P&E arch issues & config with proxmox, and there was a statement (at least for PVE7) that on startup, container cores are allocated and can't be switched over during operation if for example higher load is required.

here at 6:43

So my questions are:
1. is that true
2. is there a way "break those loose" ?
 
This is something PVE will need to improve upon. Currently we just spread containers across cpus - that is if a core count is set for a container.

If you have P+E cores I currently recommend settings the core count to 0 (unlimited) and use the cpu limits instead and let the scheduler do its thing. (I mean, I generally recommend this, as pinning to cores is usually not the best way to squeeze out performance, but some people "need" it...)

Tracking this in #4968[0]

[0] https://bugzilla.proxmox.com/show_bug.cgi?id=4968
 
Thanks for clarification !
(and I was afraid you'll confirm it :( )

About setting the core count to "0" - GUI doesn't even allow this. Is that a "supported" feature, or something that works from config level just because it was overlooked and in near future it could break all my CT ? Also for quite some of my containers, the unlimited cpu is not really an option ... and moving those to vm would be a true hassle, so it would be nice if that downside of CT on proxmox could get resolved.

Sidenote: this also explains why containers somehow behaved "weird" in terms of performance.
 
Actually, I've started an issue on LXC github to see what they've got. @wbumiller you might be interested in the reply that I've got there:
https://github.com/lxc/lxcfs/issues/616#issuecomment-1759878400

in essence:
So instead of limits.cpu=4, maybe use limits.cpu.allowance=40ms/10ms, this will time-limit your CPU usage at 4 CPUs worth of time, considered over a time slice of 10ms but allow the scheduler to pick any core it sees fit.
Edit:
which I think could be implemented relatively easily, while still allowing people funky features like cpu pinning via config file if they REALLY REALLY want to.
which turns out can be easilly achieved with "CPU TIME" in CT cpu config tab. (yep, stupid me)
 
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