On 12/12/2010 12:04 PM, Andreas Rittershofer wrote:
Given is a situation as follows: One physical machine with 4 CPUs and 16 GB RAM. On this machine KVM and three virtual machines are installed. VM1: 2 CPUs, 8 GB RAM VM2: 2 CPUs, 6 GB RAM VM3: 1 CPU, 4 GB RAM As you can see, the sum of all virtual CPUs is greater than the number of physically available CPUs, the same with the RAM. What does happen, when all three VMs are started? They will need 5 CPUs, but only 4 CPUs are physically availabe, they will need 18 GB of RAM, but only 16 GB of RAM are physically available? What will KVM do in such a situation?
Linux will timeshare the cpus across the guests, and use swap space to provide extra memory. Both of these can reduce performance.
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