[vbox-dev] 386, 486 or 686?

[Ribhi Kamal]

Klaus,
I understand your frustration, but I think you misread my question. I
wasn't asking if the vbox emulates instructions that are not supported by
the host CPU, I was asking if the number of instructions on 386 vs. 686
which require workarounds (i.e patch manager) is different.

Assuming that 386 has less problematic instructions than 686, I should be
able to get an improved performance if I compile the Linux kernel to target
386.


On Mon, Jun 18, 2012 at 12:36 PM, Klaus Espenlaub <
klaus.espenlaub at oracle.com> wrote:

> On 18.06.2012 17:56, Ribhi Kamal wrote:
> > I'm worried that some of these relatively new instructions might add
> > more instructions that are troublesome to virtualize. So I'm inclined to
> > using the arch with the smallest feature set, 386, rather than 686. Does
> > that sound right?
>
> You expect detailed answers without giving the minimal set of facts -
> what virtualization mode are you talking about? VirtualBoxe effectively
> has 3 of them - the recompiler, raw mode and hardware virtualization. In
> the last two effectively all "normal" instructions are executed usually
> without significant overhead (ignoring interrupts/faults or unrelated
> instructions which need attention by the hypervisor). In general,
> VirtualBox tries to stay as much as possible in those two virtualization
> modes (if available - there are conditions which may force going to the
> recompiler).
>
> In any case, VirtualBox doesn't offer instructions which the host CPU
> doesn't have (and actually might disable the CPUID feature bits for some
> instruction set extensions which the CPU might have), and thus there is
> no need for completely emulating something in software (the recompiler
> often does it nevertheless, just to have everything under control).
>
> So don't worry too much about those fuzzy "relatively new instructions".
>
> Klaus
>
> > On Mon, Jun 18, 2012 at 10:58 AM, Alexey Eromenko <al4321 at gmail.com
> > <mailto:al4321 at gmail.com>> wrote:
> >
> >     On Mon, Jun 18, 2012 at 5:51 PM, Ribhi Kamal <rbhkamal at gmail.com
> >     <mailto:rbhkamal at gmail.com>> wrote:
> >      > >From a Virtualbox point of view, would a Linux kernel be
> >     easier/faster
> >      > to virtualize if it was targeted for a 386 CPU architecture, 486
> >     or 686?
> >      > Would it make a difference at all?
> >
> >     I think 686 would be faster, as more instructions are available
> >     (MMX, cmov, ...)
> >
> >     --
> >     -Alexey Eromenko "Technologov"
> >
> >     _______________________________________________
> >     vbox-dev mailing list
> >     vbox-dev at virtualbox.org <mailto:vbox-dev at virtualbox.org>
> >     https://www.virtualbox.org/mailman/listinfo/vbox-dev
> >
> >
> >
> >
> > --
> > -- Ribhi
> >
> >
> > _______________________________________________
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>
>
> --
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> Virtualization
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-- 
-- Ribhi
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