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Old 10-01-2010, 05:10 AM   #1
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Allocation of CPU Cores on RHEV-H

Hi All,

Can you please explain what will happen in the following scenario:

I have 16 Cores on RHEV-H. If I create 5 VMs with 4 Cores to each then how VMs will share the Cores and what will happen if CPU load is very high(near to 95%)?

Thanks and Regards
Shiva Kumar Gone
Old 10-02-2010, 02:26 PM   #2
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Well I'm not sure exactly if RHEV-H makes nay further configuration about it, but KVM will allow you to peg certain cores to certain VM's, allowing you to partition off as many cores as you want, which will then be freely contended within each cores permitted guests vms
Old 10-03-2010, 07:49 AM   #3
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you can always open a support ticket with RHT and ask
Old 10-05-2010, 11:07 PM   #4
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So, you have an over commit situation. If I understand you correctly, you've created a scenario that requires more cores than what you actually have to give... as expected, performance is going to drop off dramatically (under high loads across all). Virtualization is designed to make effective use of under utilized hardware resources. It's not a miracle maker. Thus if you have 20 guests that aren't used much and a total of 16 cores, things work great if each guest uses one core.

If you have one guest that needs more resources, dedicate more to it. But IMHO, you've created a scenario that doesn't work well.... right? Or am I missing something?

Also, this problem could be worse if those aren't TRUE cores (e.g. Intel Hyperthreads).

First rule of virtualization, start guests off with the minimum resources you can give them. Then examine utilization and bump where needed.
Old 10-12-2010, 06:05 AM   #5
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Thanks for the reply.

My doubt got clarified. Performance is really poor when we over commit the resources.

Thanks and Regards
Shiva kumar Gone


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