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] [PATCH][RESUBMIT] don't schedule unplugged vcpus

To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH][RESUBMIT] don't schedule unplugged vcpus
From: Ryan Harper <ryanh@xxxxxxxxxx>
Date: Wed, 8 Jun 2005 17:00:04 -0500
Cc: Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Ryan Harper <ryanh@xxxxxxxxxx>
Delivery-date: Wed, 08 Jun 2005 21:59:22 +0000
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <0e458b5371820d127c90ac838f760c9c@xxxxxxxxxxxx>
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/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <A95E2296287EAD4EB592B5DEEFCE0E9D28213A@xxxxxxxxxxxxxxxxxxxxxxxxxxx> <0e458b5371820d127c90ac838f760c9c@xxxxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
User-agent: Mutt/1.5.6+20040907i
* Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> [2005-06-08 16:57]:
> On 8 Jun 2005, at 22:42, Ian Pratt wrote:
> >I don't see why we care about vcpus that are down. From the user's 
> >point
> >of view they've gone for good -- it just happens that Xen hasn't freed
> >the memory in anticipation of it being used again. What do you think?
> >
> >I'd be inclined just to enter '-1' in the vcpu_to_cpu map. BTW: we 
> >could
> >make it an s16 rather than s32 at the same time. I think 32,768 CPUs
> >should keep be enough for anyone :-)
> This is how I view it. We don't free the vcpu structure only because it 
> isn't reference counted. We can only be sure that noone has a reference 
> to the structure when the entire domain's refcnt falls to zero. Given 
> the small amount of memory involved, it's not worth the pain or 
> run-time cost of adding per-vcpu reference counts.
> So VCPU_down == invisible outside Xen.

So, when I trigger a vcpu to go down via dom0 xm operation, I have to
trust that it worked?  I have no way of knowing at some point later
which vcpus are up or down?  I don't see any cost to this other than
during the getdominfo hcall.  

Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
(512) 838-9253   T/L: 678-9253

Xen-devel mailing list