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Re: [Xen-devel] [PATCH 0 of 5] v2: Nested-p2m cleanups and locking chang

To: Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH 0 of 5] v2: Nested-p2m cleanups and locking changes
From: Christoph Egger <Christoph.Egger@xxxxxxx>
Date: Mon, 27 Jun 2011 15:24:05 +0200
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On 06/27/11 15:20, Tim Deegan wrote:
At 14:15 +0100 on 27 Jun (1309184128), Tim Deegan wrote:
At 14:23 +0200 on 27 Jun (1309184586), Christoph Egger wrote:
  - Why is there a 10x increase in IPIs after this series?  I don't see
    what sequence of events sets the relevant cpumask bits to make this
    happen.

In patch 1 the code that sends the IPIs was outside of the loop and
moved into the loop.

Well, yes, but I don't see what that causes 10x IPIs, unless the vcpus
are burning through np2m tables very quickly indeed.  Maybe removing the
extra flushes for TLB control will do the trick.  I'll make a patch...

Hmmm, on second thoughts, we can't remove those flushes after all.
The np2m is in sync with the p2m but not with the guest-supplied p2m,
so we do need to flush it when the guest asks for that to happen.

Right. I thought on that when I developped the code but then I forgot.
We should add a comment.

Christoph


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