Shane O''Donnell \(shodonne\)
2005-Aug-17 20:44 UTC
RE: [Xen-users] Re: [Xen-devel] VMX Hardware
I hope you aren''t in a hurry to do your benchmarking on AMD''s Nested Page Tables since their initial launch of Pacifica won''t include this support. This info came from an AMD "fellow" (sorry--names have eluded me--"Richard Brunner" seems right) at the Xen BoF @ Linux World (8/10) who indicated that this functionality will be added in later. This was the same BoF where Intel demonstrated Win XP running natively on Xen on a development VT platform -- good stuff. Disclaimer: Intel also noted at the same meeting that their ultimate for roadmap for VT (the new name for Vanderpool) will also be delivered in staged releases. Shane O. -----Original Message----- From: xen-users-bounces@lists.xensource.com [mailto:xen-users-bounces@lists.xensource.com] On Behalf Of Keir Fraser Sent: Sunday, August 14, 2005 2:23 PM To: Anthony Liguori Cc: Goetz Bock; xen-devel@lists.xensource.com; xen-users@lists.xensource.com; monz@danbbs.dk Subject: Re: [Xen-users] Re: [Xen-devel] VMX Hardware On 14 Aug 2005, at 19:09, Anthony Liguori wrote:> The Pacifica spec does mention optional hardware support for "Nested > Page Tables" which is essentially hardware shadow page tables. > > Should be interesting to see the performance difference between > software/hardware shadow page tables.I have doubts about the performance of hardware page tables, unless there''s a clever TLB design. A pagetable walk which is four memory accesses on normal x86/64 becomes twenty accesses in nested mode! It may be that shadow pagetables, by providing a bigger ''cache'' for guest->host mappings, can actually perform better on many workloads. I guess we''ll see -- if silicon is produced that supports that mode, someone is bound to add support to Xen. -- Keir _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users