This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
Home Products Support Community News


Re: [Xen-devel] increase evtchn limits

To: Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
Subject: Re: [Xen-devel] increase evtchn limits
From: Zhigang Wang <zhigang.x.wang@xxxxxxxxxx>
Date: Fri, 21 May 2010 13:07:42 +0800
Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
Delivery-date: Thu, 20 May 2010 22:09:00 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <20100520204110.2d421bfe@xxxxxxxxxxxxxxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <20100520204110.2d421bfe@xxxxxxxxxxxxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20100301 Fedora/3.0.3-1.fc12 Thunderbird/3.0.3
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


> 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
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-devel

Xen-devel mailing list