WARNING - OLD ARCHIVES

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/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

Re: [Xen-devel] A question no one can answer

To: "Alan Cox" <alan@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] A question no one can answer
From: "Dan Doucette" <doucette.daniel@xxxxxxxxx>
Date: Fri, 15 Feb 2008 11:56:37 -0800
Cc: weiming <zephyr.zhao@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Robert Stober <rstober@xxxxxxxxxxxx>
Delivery-date: Fri, 15 Feb 2008 11:57:05 -0800
Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:received:received:message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:references; bh=Sxq0LWgTfPO+axEdj7giAb0iJI0VjmLBbuanJG+9TaY=; b=R/I4yz+7YhlVhGDhsAx07j0Te4l78lRE7U9+IjZdqNCdkfw9SOKSyOSfY+uFMKIyPkUcNm2clhgTN5R3MA/xsPDdWdkSWPW2QWCPjPYnTu2ZO+CzDA9v6edsoO/ZduMYD9mz2btbmUS5kNQr4vDGJH+XPDdWH81TXQp+0G8Qknw=
Domainkey-signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:references; b=x9Z2V/jBi6PiDnaKSpSa/Bt/R+6IBe1gmhMmXKFSzWrB7skrN+58QNqZ3WS7Ls5gGjxnmocNfnQ5xNGiQCL6/NstjT2NzqH/9Z/iQP/hQyN8mZCl71TRXOJ02g8O6aBuJ29MGUYvzgluwt4LDE53kC16rzVCDIbIZCUmtHLhUG8=
Envelope-to: www-data@xxxxxxxxxxxxxxxxxx
In-reply-to: <20080215130522.2c258316@core>
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: <3825A1772E68364B942CF6DBDF41C8BB04B8F3E2@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> <add59a3f0802141901i29686fe9s1039de21d0fe305d@xxxxxxxxxxxxxx> <3825A1772E68364B942CF6DBDF41C8BB04B8F3E3@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> <20080215130522.2c258316@core>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Hello Robert and others,
 
Below is a link to a presentation given at a conference last summer, where the authors used cache colour allocation schemes to limit L2 cache overuse by an application. 
If your goal is to create a fair memory share per-guest (bandwidth or otherwise), you may want to consider the possibility of managing it from a level closer to the CPU.
 
 
Dan.
 


 
On Fri, Feb 15, 2008 at 5:05 AM, Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> wrote:
On Thu, 14 Feb 2008 22:24:18 -0500
"Robert Stober" <rstober@xxxxxxxxxxxx> wrote:

> Weiming,
>
> I agree that it is very hard, and that no one has done it. But
> nevertheless I suggest the following question to the Xen developers:
>
> Given the fact that memory bandwidth is shared amongst multiple cores on
> a single die, assume that one VM is running on each core. What is to
> stop one VM from saturating the memory bus, causing reduced performance
> of all the other VMs? This is the general multi-core problem, not
> specific to Xen. But it affects Xen greatly. What use is it to allocate
> memory to a VM if it can't use the memory because a process of another
> VM has saturated the memory bus?

Its perfectly doable on modern x86 - you use the profiling registers and
set them up so you get a threshold interrupt when too much main memory
traffic is counted (which you use to reschedule punishing the memory
user). There are research papers on it from quite a long time back but
afaik nobody ever implemented it in production although its not too hard
to do so might be an interesting project.

Alan

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

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