Re: [Xen-users] best way to optimize use of CPU and IO

["Fajar A. Nugraha" <fajar@xxxxxxxxx>]

Fong Vang wrote:
> I have a system with 2 quad core CPUs running Xen on CentOS 5.1 
> 64-bit.  The kernel sees this system as having 8 CPUs.  If I were to 
> create 6 domUs, what would be the best way to allocate the CPUs to get 
> best CPU and IO performance?  Should all CPUs be allocated to all domU 
> and let the system allocate as it sees fit or would the system perform 
> better if each domU is restricted to fewer CPUs?
> Each domU is running a custom Java application that utilizes MySQL 
> heavily.  Application is heavily threaded. 
As a rule of thumb, performance-wise, virtualization is best when you 
have under-utilized systems. Meaning, you'll need to know the load 
characteristic of each domU. Not-so-busy systems can be grouped 
togethere, while busy systems might be better of on a separate physical 
system. Since dom0 handles actual disk/network I/O, you should give it a 
dedicated core/cpu.
A somewhat simple way to get domU load :
- set each domU to have 1 cpu, each on different dom0 physical cpu (use 
vcpus and cpus on xen config file)
- limit dom0 to use only the CPU that domU doesn't use (xm vcpu-set, xm 
vcpu-pin)
- put each domU's disk on LVM on dom0.
- run all domU
- use "xm top", you'll get CPU and block device read/writes per domU
- use "iostat -x", you'll get disk usage rate of each LV

depending on the result, you might need to move some domUs to a separate 
server, assign some domUs more CPUs than others, or have several domUs 
share a single CPU.
Regards,

Fajar

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