From mboxrd@z Thu Jan  1 00:00:00 1970
From: Keir Fraser <keir.fraser@eu.citrix.com>
Subject: Re: question on iommu _map_page
Date: Fri, 2 Jul 2010 08:13:41 +0100
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To: Kaushik Kumar Ram <kaushik@rice.edu>
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On 02/07/2010 07:22, "Kaushik Kumar Ram" <kaushik@rice.edu> wrote:

>> See if xen-unstable:21597 works for you.
> 
> Keir,
> 
> I finally found some time to test your patch. While it seems to fix the
> problem, it *significantly* degrades performance.
> On running netperf, there is a 10X reduction in throughput to a guest VM. On
> profiling, I find a significant number of cycles
> being spent in mapcount(). In the current solution, the entire grant table is
> searched every time (right ?). The mapping info
> ought to be stored in some per-page location... for efficient access.

It needs to be a per-mapping-domain location. Like the VT-d pte itself.
Patches welcome.

 -- Keir