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Re: [Xen-devel] PAE issue (32-on-64 work)

  • To: Joe Bonasera <joe.bonasera@xxxxxxx>
  • From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
  • Date: Thu, 19 Oct 2006 19:48:43 +0100
  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Thu, 19 Oct 2006 12:00:17 -0700
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AcbzrzMscfDI4l+iEduNyQANk04WTA==
  • Thread-topic: [Xen-devel] PAE issue (32-on-64 work)

On 19/10/06 6:22 pm, "Joe Bonasera" <joe.bonasera@xxxxxxx> wrote:

>> You should just allocate a page-sized L3 per process and be done with it. A
>> page overhead per process is nothing to be concerned about (clearly the
>> overhead can be even bigger if, for example, you run 4-level tables on
>> x86_64). Recopying the L3 entries every TLB flush will *not* perform well on
>> current Xen.
> Well we actually don't do complete TLB flushes very often at all, essentially
> only the first time a new L3 entry is created by a running process which
> for most processes means never - as >1Gig processes are rare.
> So it shouldn't matter if they hit one or two slowish flushes.
> Are there any other performance implications to watch out for?

I don't think so. Just remember that PAE L3 entry updates are not fast. We
really expect it only to happen on process creation/destruction (or similar

 -- Keir

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