Re: [Xen-devel] NR_IRQ limit

[Eric Windisch <eric@xxxxxxxxxxxx>]

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

> Eric,
> 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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