There is ALOT of misleading articles both dotted around the web and these forums in regards to vCPU allocation, expecially when you take into account modern CPUs with support for Hyper threading.
I have a xen server, it's running a slightly older CPU but capable. The Host is running a dual slot, 6 Physical core cpu. With HT this would mean Xen server sees a total of 24 vCPUs (2x6+HT).
I have read some articles that start Dom0 should be set to 50% of your VCPUs so in my case it should be 12, but then there are just as many contradicting articles that say to set Dom0 to 50% of you PHYSICAL cores, so in my case that would be 6. Who is correct?
Then we move onto the actual Guests and their topoligy. If I don't want to over provision, and I did set Dom0 to 50% this would leave either 12 or 18 VCPUs but how do you tie this into physical requirements vs xen server.
Lets say Windows Server min spec was a 4 core CPU. This would mean 4 Phyical cores it would never be 2 Cores + HT. How would you set this up in Xen. Would you pick 4Cpus, but then you can change the topology ( 1x4, 2x2 and 4x1) why would that really matter. Because these are VCPUs they aren't going to have the same sort of benefits as a physical server with duals sockets (allowing for better memory management, cache and pci lanes) so in terms of Xen which topology is correct.
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Jeremy Brook
There is ALOT of misleading articles both dotted around the web and these forums in regards to vCPU allocation, expecially when you take into account modern CPUs with support for Hyper threading.
I have a xen server, it's running a slightly older CPU but capable. The Host is running a dual slot, 6 Physical core cpu. With HT this would mean Xen server sees a total of 24 vCPUs (2x6+HT).
I have read some articles that start Dom0 should be set to 50% of your VCPUs so in my case it should be 12, but then there are just as many contradicting articles that say to set Dom0 to 50% of you PHYSICAL cores, so in my case that would be 6. Who is correct?
Then we move onto the actual Guests and their topoligy. If I don't want to over provision, and I did set Dom0 to 50% this would leave either 12 or 18 VCPUs but how do you tie this into physical requirements vs xen server.
Lets say Windows Server min spec was a 4 core CPU. This would mean 4 Phyical cores it would never be 2 Cores + HT. How would you set this up in Xen. Would you pick 4Cpus, but then you can change the topology ( 1x4, 2x2 and 4x1) why would that really matter. Because these are VCPUs they aren't going to have the same sort of benefits as a physical server with duals sockets (allowing for better memory management, cache and pci lanes) so in terms of Xen which topology is correct.
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