Reducing Processor Count

[LM_Chris]

I have been having a performance problem with a few of our Linux systems (CentOS 5.5). I think I may have figured out the cause but would like confirmation from someone else. I think it is possible that I built my template with two processors. When I deployed from these templates I may have reduced the processor count down to one. Would this cause some noticable performance problems?

[AWo]

Yes, that is possible. If the template has a multiprocessor kernel you might need to switch to a uniprocessor one.

AWo

VCP 3 & 4

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[jamesbowling]

It is completely possible. When you installed the original template VM you were installing CentOS with the SMP kernel. Changing that from 2 vCPU to 1vCPU would mean that you are now running a single proc on a SMP kernel. This could possibly cause some issues.

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[thakala]

Which OS type are you running 32-bit or 64-bit?

If you are running 64-bit Linux there is no uniprocessor kernel for that, but you can configure x64 kernel for uniprocessor system by passing "nosmp" kernel parameter at grub.conf. To get absolutely maximum performance with uniprocessor Linux VM pass all these parameters "divider=10 nosmp noapic nolapic"

- divider=10 will slow Linux interrupt timer from 1000 Hz to 100 Hz, this will reduce idle time CPU consumption.

- nosmp will configure kernel to uniprocessor mode

- noapic will turn off APIC support which isn't needed on uniprocessor system

- nolapic will turn off local APIC support which also isn't needed on uniprocessor system

Tomi

http://v-reality.info

[mcowger]

No - unlike in windows, Linux has no penalty for running SMP kernel on a UP system.

--Matt
VCP, VCDX #52, Unix Geek, Storage Nerd

[jamesbowling]

Ah, I wasn't aware! Learn something new everyday! I always thought that the kernel was tuned specifically for SMP if that is used as opposed to uniproc.

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[LM_Chris]

I made the changes. I'll wait and see what my end-users report.