Re: [Xen-devel] increase evtchn limits

[Zhigang Wang <zhigang.x.wang@xxxxxxxxxx>]

On 05/21/2010 11:41 AM, Mukesh Rathor wrote:
> Hi,
> 
> I'm trying to boot up with lot more than 32 vcpus on this very large box.
> I overcame vcpu_info[MAX_VIRT_CPUS] by doing vcpu placement hypercall
> in guest, but now running into evt channel limit (lots of devices):
> 
>        unsigned long evtchn_pending[sizeof(unsigned long) * 8];
> 
I'm not sure, but it seems: 1024 for 32bit and 4096 for 64bit.

32bit: 4 * (4 * 8) * 8 = 1024
64bit: 8 * (8 * 8) * 8 = 4096

zhigang

> which limits to 512 max for my 64bit dom0. The only recourse seems to 
> create a new struct shared_info_v2{}, and re-arrange it a bit with lot 
> more event channels. Since, start_info has magic with version info, I 
> can just check that in guest and use new shared_info...(doing the design 
> on the fly here). I can create a new vcpuop saying the guest is using 
> newer version.  Or forget new version of shared_info{}, I can just
> put evtchn stuff in my own mfn and tell hypervisor to relocate it,
> (just like vcpu_info does) via new VCPUOP_ call.
> 
> Keir, what do you think?
> 
> thanks,
> Mukesh
> 
> 
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