Re: increasing the number of guests (NR_DYNIRQS)

[Tim Post <echo@echoreply.us>]

On Sat, 2010-02-20 at 05:53 -0500, Luke S Crawford wrote:
> So I'm setting up a server to host many very small domains, and I ran
> into a problem where after I create about 60 guests, any addtional guests
> start, but hang at 0 cpu usage-  they never do anything.  
> 
> grep Dynamic-irq /proc/interrupts | wc -l
> 256
> 
> 
> I did some digging and found some old discussion of the topic[1]
> and but the patches discussed there didn't work, I assume because the
> linux/xen codebase has evolved since then.  I dug around and made this 
> change:
> 
> xen-3.4-testing.hg/linux-2.6.18-xen.hg/include/asm-x86_64/mach-xen/irq_vectors.h
> 
> I changed:
> 
> #define NR_DYNIRQS           1024
> 
> (it defaults to 256)

I've done the same thing several times without breaking anything. What I
could not see is how much more expensive 1024 is than 256. Like you, I
had hosts with guests way north of 200 that did very little, so ...

Cheers,
--Tim