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Re: [Xen-devel] [PATCH] [VTD] Separate VT-d page table from P2M table

To: "Han, Weidong" <weidong.han@xxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] [VTD] Separate VT-d page table from P2M table
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Tue, 22 Apr 2008 10:37:25 +0100
Cc: "Xu, Anthony" <anthony.xu@xxxxxxxxx>, "Kay, Allen M" <allen.m.kay@xxxxxxxxx>
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Thread-topic: [Xen-devel] [PATCH] [VTD] Separate VT-d page table from P2M table
User-agent: Microsoft-Entourage/
What are the tradeoffs? One obvious tradeoff is that separate tables doubles
the memory overhead. What are the advantages of separate tables? I believe
currently we share the pagetables (right?). If so, why would we even
consider moving to separate tables?

 -- Keir

On 22/4/08 10:34, "Han, Weidong" <weidong.han@xxxxxxxxx> wrote:

> Separate VT-d page table is by default. Shared VT-d page table may be
> easy and good in some cases. So we let them co-exist now. If shared VT-d
> page table is not necessary and useless, we can remove it easily in
> future.
> Randy (weidong)
> Keir Fraser wrote:
>> On 22/4/08 09:36, "Han, Weidong" <weidong.han@xxxxxxxxx> wrote:
>>> Currently VT-d page table shares with P2M table, this patch supports
>>> separate VT-d page table. 1) add an option (vtd_share) to control
>>> whether VT-d page table shares with P2M table or not.
>> Why? Is this just another option that noone will understand.
>>  -- Keir

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