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RE: ´ð¸´: [Xen-ia64-devel] Re: [PATCH 0/12] various fixes related the xe

To: "de Dinechin, Christophe (Integrity VM)" <christophe.de-dinechin@xxxxxx>
Subject: RE: ´ð¸´: [Xen-ia64-devel] Re: [PATCH 0/12] various fixes related the xenrelocation
From: tgingold@xxxxxxx
Date: Tue, 08 Jan 2008 15:46:11 +0100
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Quoting "de Dinechin, Christophe (Integrity VM)"

> >> Well, we used to boot with IDE a long time ago, but we have dropped
> >> IDE support for so long that I cannot really tell if a modern HPUX
> >> can still boot that way.
> >
> > Can you boot from CD ?
> > Which disk controller does HP support and which one does the HP VM
> > emulate ? (If you are allowed to answer!)
> You can boot HPUX from CD (DVD actually). I do not know the exact list of
> disk controllers. HPVM now emulates MPT SCSI as a disk controller, and the
> Intel i82546 for networking. It's not a secret, any customer can tell by
> looking at the hardware from within an HPVM guest :-) For HPUX, we also have
> "accelerated" drivers starting with HPVM version 3.5. Also not a secret, it's
> one of the selling points of that version :-)
> For example, here is what lspci says on one of my Linux guests:
> 00:00.0 SCSI storage controller: LSI Logic / Symbios Logic 53c1030 PCI-X
> Fusion MPT Dual Ultra320 SCSI (rev 07)
> 00:01.0 Ethernet controller: Intel Corporation 82540EM Gigabit Ethernet
> Controler
> 00:03.0 ISA bridge: Intel Corporation 82372FB PIIX5 ISA (rev 01)
> The physical devices we emulate were chosen because they were supported by
> all guest operating systems we cared about, and their design made it possible
> to get relatively good performance when virtualized. However, they are not
> the simplest to emulate.

Xen is far behind as all devices emulated are rather old devices.
(I once tried to find the spec of 53c1030 but was not lucky.)

> Do you have rough performance benchmarks for Xen running a VT-i guest right
> now? We discarded trap-and-emulate very early in the HPVM design because an
> early experiment had shown that on Itanium, fault handling alone amounted to
> something like 15% performance degradation. This may have changed with more
> recent chips, but I'm curious about this.

I don't have figure but maybe some were sent in the mailing list.  For sure
VT-i degradation is severe.  The Xen approach is para-virtualization where a
tiny part of the OS is rewritten.  This approach is very effective but works
only for open source OSes.


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