<div>Klaus,</div><div>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.</div>
<div><br></div><div>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.</div><div><br></div><br><div class="gmail_quote">
On Mon, Jun 18, 2012 at 12:36 PM, Klaus Espenlaub <span dir="ltr"><<a href="mailto:klaus.espenlaub@oracle.com" target="_blank">klaus.espenlaub@oracle.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div class="im">On 18.06.2012 17:56, Ribhi Kamal wrote:<br>
> I'm worried that some of these relatively new instructions might add<br>
> more instructions that are troublesome to virtualize. So I'm inclined to<br>
> using the arch with the smallest feature set, 386, rather than 686. Does<br>
> that sound right?<br>
<br>
</div>You expect detailed answers without giving the minimal set of facts -<br>
what virtualization mode are you talking about? VirtualBoxe effectively<br>
has 3 of them - the recompiler, raw mode and hardware virtualization. In<br>
the last two effectively all "normal" instructions are executed usually<br>
without significant overhead (ignoring interrupts/faults or unrelated<br>
instructions which need attention by the hypervisor). In general,<br>
VirtualBox tries to stay as much as possible in those two virtualization<br>
modes (if available - there are conditions which may force going to the<br>
recompiler).<br>
<br>
In any case, VirtualBox doesn't offer instructions which the host CPU<br>
doesn't have (and actually might disable the CPUID feature bits for some<br>
instruction set extensions which the CPU might have), and thus there is<br>
no need for completely emulating something in software (the recompiler<br>
often does it nevertheless, just to have everything under control).<br>
<br>
So don't worry too much about those fuzzy "relatively new instructions".<br>
<br>
Klaus<br>
<div class="im"><br>
> On Mon, Jun 18, 2012 at 10:58 AM, Alexey Eromenko <<a href="mailto:al4321@gmail.com">al4321@gmail.com</a><br>
</div><div class="im">> <mailto:<a href="mailto:al4321@gmail.com">al4321@gmail.com</a>>> wrote:<br>
><br>
> On Mon, Jun 18, 2012 at 5:51 PM, Ribhi Kamal <<a href="mailto:rbhkamal@gmail.com">rbhkamal@gmail.com</a><br>
</div><div class="im">> <mailto:<a href="mailto:rbhkamal@gmail.com">rbhkamal@gmail.com</a>>> wrote:<br>
> > >From a Virtualbox point of view, would a Linux kernel be<br>
> easier/faster<br>
> > to virtualize if it was targeted for a 386 CPU architecture, 486<br>
> or 686?<br>
> > Would it make a difference at all?<br>
><br>
> I think 686 would be faster, as more instructions are available<br>
> (MMX, cmov, ...)<br>
><br>
> --<br>
> -Alexey Eromenko "Technologov"<br>
><br>
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><br>
><br>
><br>
><br>
> --<br>
> -- Ribhi<br>
><br>
><br>
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--<br>
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</div></div></blockquote></div><br><br clear="all"><div><br></div>-- <br>-- Ribhi<br>