|
xen-users
RE: [Xen-users] Xen 3.0 and resources guarantees - CPU, RAM...
> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of
> Jordi Segues
> Sent: 22 January 2007 15:09
> To: xen-users@xxxxxxxxxxxxxxxxxxx
> Cc: Jordi Segues (Gmail)
> Subject: [Xen-users] Xen 3.0 and resources guarantees - CPU, RAM...
>
> Hello,
>
> This is my first post in the mailing list. :)
> I'm planning to use xen to virtualize some servers.
> So I'm looking for info about resources guarantees, specially for CPU
> and RAM for guests (and Dom0).
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).
I'm not quite sure about the limiting of CPU usage.
>
> I've seen that in the conf file of each guest you can specify vcpu,
> cputime and memory.
> So in other documents and comparison between virtualization
> technologies I've read that XEN doesn't provide resources guarantees,
> and that you can't reserve CPU for each guest.
>
> 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).
There are settings in the current scheduler, which allows you to set various
caps and shares of CPU-time, but if it can do what you want or not, I can't
really say.
> How do you define how many vcpus you hardware have?
By setting VCPUS=n in the config file.
> How do I have to understand cputime?
As for above vcpu & cputime...
> 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.
Although, if you have sufficient number of CPU's, you can dedicate one CPU to a
particular guest, and that should guarantee that guest a certain amount of
CPU-time. If only one guest is using a CPU, then it would obviously be idle if
that guest is idle.
> Does memory parameter guaratees that amount of memory to the guest?
Yes, for sure (although there are things you can do to "move" memory between
guests).
>
> I've heard about Shareguard and SEDF-DC? Is this necessary with xen
> 3.0 or are similar features implemented in xen 3.0? (through vcpu,
> cputime...)
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.
I'm sorry I can't answer better than this....
--
Mats
>
> PLEASE, could someone clear this?
>
> Thank you very much in advance!
>
> --
> Jordi Segués Daina
>
> _______________________________________________
> Xen-users mailing list
> Xen-users@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-users
>
>
>
_______________________________________________
Xen-users mailing list
Xen-users@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-users
|
|
|
Home