Re: [ovirt-users] several ovirt questions - CPU allocation, and use threads as CPU

2015-11-19 Thread Martin Sivak 
Hi Jason,

> How do I go about seeing how many CPUs I've allocated across all the VMs on a 
> host?
> If shared CPUs are possible, can I specify VMs that are allowed to shared 
> CPUs versus
>  VMs that reqiure dedicated CPUs?

Unfortunately the UI is lacking in this area. We do not currently have
any overview page.

Also we do not currently support dedicated CPU to VM mapping. You can
use CPU pinning to select the CPUs that should be used, but the CPU
can be used for any other VM too (so it is a limitation for the VM
assignment, not for the CPU assignment).

There might be a workaround for this using the isolcpus
(http://www.linuxtopia.org/online_books/linux_kernel/kernel_configuration/re46.html)
kernel boot option and then puting VMs on those CPUs using pinning.
But we have never tested this.

> What happens if I allocate more cores than what I actually have?

We won't allow your VM to start if it requires more cores than
physically available on the destination host.

> If I specify say, a dual CPU system, would that system show up as 4 cores (2 
> real cores and 2 hyper-threaded cores)

CPU pinning and core reporting always use thread IDs so it makes no
difference there.

But the scheduling takes this option into account when computing the
load or when checking if enough cores are available (useful with
relation to your previous question).


Would you care to open a bug about the CPU pinning overview? It might
be a nice RFE considering we have something similar for NUMA already.

Best regards

Martin Sivak
SLA / oVirt


On Tue, Nov 17, 2015 at 4:52 AM, Jason Keltz  wrote:
> Hi.
>
> When I go to the "Clusters" in ovirt engine, I can see the total number of
> VMs in the cluster.   If I open up "Hosts", I can see how many VMs are
> running on each host.  I can see the memory consumption as well.  How do I
> go about seeing how many CPUs I've allocated across all the VMs on a host?
> What happens if I allocate more cores than what I actually have? If shared
> CPUs are possible, can I specify VMs that are allowed to shared CPUs versus
> VMs that reqiure dedicated CPUs?  Finally, I presently have "Use Threads as
> CPUs" off.  I don't remember if that was the default, or whether I selected
> that option during installation.  Is there any disadvantage to turning it
> on?  I realize that those other cores aren't "real" cores - they're the
> hyper-threading course,  but it's not clear how ovirt would handle those
> cores.  If I specify say, a dual CPU system, would that system show up as 4
> cores (2 real cores and 2 hyper-threaded cores) ?
>
> Thanks for any help..
>
> Jason.
>
>
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Re: [ovirt-users] several ovirt questions - CPU allocation, and use threads as CPU

2015-11-19 Thread Jason Keltz 


On 11/19/2015 06:00 AM, Martin Sivak wrote:

Hi Jason,


How do I go about seeing how many CPUs I've allocated across all the VMs on a 
host?
If shared CPUs are possible, can I specify VMs that are allowed to shared CPUs 
versus
  VMs that reqiure dedicated CPUs?

Unfortunately the UI is lacking in this area. We do not currently have
any overview page.

I will submit an RFE when I get a chance.


Also we do not currently support dedicated CPU to VM mapping. You can
use CPU pinning to select the CPUs that should be used, but the CPU
can be used for any other VM too (so it is a limitation for the VM
assignment, not for the CPU assignment).

There might be a workaround for this using the isolcpus
(http://www.linuxtopia.org/online_books/linux_kernel/kernel_configuration/re46.html)
kernel boot option and then puting VMs on those CPUs using pinning.
But we have never tested this.

Ok.

What happens if I allocate more cores than what I actually have?

We won't allow your VM to start if it requires more cores than
physically available on the destination host.

Actually, I think I wasn't clear with my message.  If I have only 4 
cores total, and I try to allocate 5 cores to one VM, I would expect the 
VM wouldn't start.  What I want to understand is what happens when I try 
to run 3 x 4 core VMs on a 4 core system.  By default, they would all 
share the 4 cores?  oVirt would never tell me that I am out of capacity 
as long as the VMs that I'm running are all under the total number of 
cores in the system?



If I specify say, a dual CPU system, would that system show up as 4 cores (2 
real cores and 2 hyper-threaded cores)

CPU pinning and core reporting always use thread IDs so it makes no
difference there.

But the scheduling takes this option into account when computing the
load or when checking if enough cores are available (useful with
relation to your previous question).
You didn't mention whether I'm at an advantage to enable "Use Threads as 
CPUs" or to leave it off?


Would you care to open a bug about the CPU pinning overview? It might
be a nice RFE considering we have something similar for NUMA already.

Sure!

Thanks!

Jason.

On Tue, Nov 17, 2015 at 4:52 AM, Jason Keltz  wrote:

Hi.

When I go to the "Clusters" in ovirt engine, I can see the total number of
VMs in the cluster.   If I open up "Hosts", I can see how many VMs are
running on each host.  I can see the memory consumption as well.  How do I
go about seeing how many CPUs I've allocated across all the VMs on a host?
What happens if I allocate more cores than what I actually have? If shared
CPUs are possible, can I specify VMs that are allowed to shared CPUs versus
VMs that reqiure dedicated CPUs?  Finally, I presently have "Use Threads as
CPUs" off.  I don't remember if that was the default, or whether I selected
that option during installation.  Is there any disadvantage to turning it
on?  I realize that those other cores aren't "real" cores - they're the
hyper-threading course,  but it's not clear how ovirt would handle those
cores.  If I specify say, a dual CPU system, would that system show up as 4
cores (2 real cores and 2 hyper-threaded cores) ?

Thanks for any help..

Jason.


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[ovirt-users] several ovirt questions - CPU allocation, and use threads as CPU

2015-11-16 Thread Jason Keltz 

Hi.

When I go to the "Clusters" in ovirt engine, I can see the total number 
of VMs in the cluster.   If I open up "Hosts", I can see how many VMs 
are running on each host.  I can see the memory consumption as well.  
How do I go about seeing how many CPUs I've allocated across all the VMs 
on a host?  What happens if I allocate more cores than what I actually 
have? If shared CPUs are possible, can I specify VMs that are allowed to 
shared CPUs versus VMs that reqiure dedicated CPUs?  Finally, I 
presently have "Use Threads as CPUs" off.  I don't remember if that was 
the default, or whether I selected that option during installation.  Is 
there any disadvantage to turning it on?  I realize that those other 
cores aren't "real" cores - they're the hyper-threading course,  but 
it's not clear how ovirt would handle those cores.  If I specify say, a 
dual CPU system, would that system show up as 4 cores (2 real cores and 
2 hyper-threaded cores) ?


Thanks for any help..

Jason.


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