several ovirt questions - CPU allocation, and use threads as CPU
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.
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/re4...) 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 <jason.keltz@gmail.com> 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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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).
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
There might be a workaround for this using the isolcpus (http://www.linuxtopia.org/online_books/linux_kernel/kernel_configuration/re4...) kernel boot option and then puting VMs on those CPUs using pinning. But we have never tested this. Ok. 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 <jason.keltz@gmail.com> 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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Martin Sivak