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

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

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
frequency).

 -- Keir



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