First of all, thanks for your answer Mats.
RAM is definitely "not a problem", as RAM is "hard limits" to each guest (and
you can either let Dom0 dole it out to other guests, or, my preferred option, by giving Dom0 a hard
limit).
Ok for the RAM
> I'm a little confused.
> How vcpu and cputime work?
Not entirely sure what you're asking (not that I'm sure I'll be able to answer
either, as I'm not that sure about how the scheduler and such works).
I mean, what's the function of a vcpu?
If I have a dual-core processor, do I have to set vcpu to 2?
Or vcpu is independent of the number of real cpus? (cause they are virtual)
Could I define 4 vcpus for a dual-core processor?
And where do you associate a vcpu to a core or cpu?
So I understand that you can associate a DomU to one or more vcpus,
and more it has, more it will have cpu time?
To give the priority to a guest I must do it giving it more vcpus?
> Are this parameters mandatorys? I mean can you reserve a CPU
> percentage or time to a guest even if it doesn't use it?
Why would you want to reserve time for a guest that then doesn't use it? That's
not meaningfull, the whole point of virtualization is to improve the
utilization of machines... So if the CPU is stting idle for guest 3, why not
run guest 2 that is needing CPU time.
Ok, you're right.
So if a guest uses 100% of the cpu, and another guest wants cpu too,
then each guest will have 50% right?
And what if I want one guest to have 2/3 of the cpu and the other 1/3?
Can you give a guest various vcpus?
SEDF (which I believe stands for Schedule Earliest Deadline First), used to be the default, but now it's
using a "Credit Scheduler", which allows "work conservation", which means that an idle
CPU can be used to "migrate" a VCPU from one CPU to another in the same system, which means that
the idle time is reduced if two competing runnable VMs happen to be on the same CPU.
This is interesting, it means you don't associate a vcpu to a real core/cpu?
I don't really find clear documentation about all this.
Sorry for that question storm ;)
You help is appreciated.
--
Jordi Segués Daina
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