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I'm running a 2 processor VMWare server. We pushed it up from 1 core to 2 cores recently and noticed it is now generating large numbers of hardware interrupts, which is killing performance.

Does anyone know why this is and how to fix it, short of reverting to 1 cpu, which would also kill performance.

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* sigh * vmware is a company not a product, which of their products are you discussing here. Can you also add a LOT more detail please. – Chopper3 Feb 1 '11 at 9:07

Try finding out what kind of interrupts it's generating (using /proc/interrupts), and how many interrupts "large numbers of hardware interrupts" means?

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Hardware Interrupts are taking up to 40 per cent of CPU. – WOPR Feb 2 '11 at 23:15
I've also noticed that the Primary Disk Controller is set to PIO mode, not DMA mode. Could this be the culprit? – WOPR Feb 2 '11 at 23:15
Dunno, have u tried changing the mode? – poige Feb 3 '11 at 9:49
For future googlers: YES, PIO mode will generate loads more interrupts/CPU load. That is what DMA (Direct Memory Access) mode is for. – Gomibushi Dec 8 '11 at 11:28

From what I understand, at least some versions of VMware products don't handle multi-CPU VMs as gracefully as would be expected. The host system has to schedule time on ALL the assigned CPU cores before giving a time slice to the guest system. So your 2-core SQL Server VM will have to wait until BOTH CPU cores are available before it gets its share of cycles. It's hard to say without more info, but could this be what you're seeing?

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