Re: Some questions about x86/xen pmap

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Thu, May 07, 2009 at 04:58:21PM +0200, Jean-Yves Migeon wrote:
>> This is a different issue. While porting NetBSD/xen to amd64 I found that
>> a single 10s or even 100s of distinct APDP operations, each requiring
>> a map/unmap of ADPD. batching APDP operations would fix most of the  
>> performances issues, but I think this needs changes in UVM.
>
> Operations that are required solely by pmap? Or some sort of side effect  
> of jumping back and forth between UVM and pmap?

the later (from memory, I could be wrong)

> Issue is amd64 specific?

mostly, because on amd64/xen almost all pmap operations go though APDP.
On native x86 or xen/i386 that's not so bad because lots of pmap
operations use the currently loaded pmap's PDP.

What makes it worse is that it requires an hypercall to map APDP and another
one to unmap.

-- 
Manuel Bouyer, LIP6, Universite Paris VI.           
Manuel.Bouyer%lip6.fr@localhost
     NetBSD: 26 ans d'experience feront toujours la difference
--