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Re: [Xen-devel] NR_IRQ limit

On Feb 29, 2008, at 5:58 PM, Subrahmanian, Raj wrote:

I don't think that you need to change the NR_VECTORS value in Xen. My understanding is that these IRQs are being doled out of Dom0, and not Xen itself.

Hmm, okay.  I guess the less to change, the better.

Incidentally, we did run 320 VMs here at Unisys. Any reason you are shooting for 320 in particular?

Each guest has 64MB-256MB of ram. We plan to put 32GB of ram into this server. Considering we're slightly above 25% capacity with 80 guests, I'm guessing 4*80 = 320 is a good estimate of where we will be at 100% capacity (in terms of RAM anyway).

Also, as you increase the number of VMs, you will run out of Xen's heap (which is set at 10 or 12 MB), soon and then you will need to change that with the boot option. We set it at 64 MB, just to be safe.

It is 16MB on x86_64, according to the docs. I'll increase to 64MB as well, from what I've read I think ~320 guests will need at least 32MB.

Thanks again,

Eric Windisch

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