[Gllug] performance of xen dom0 vs native linux

[James Courtier-Dutton]

2009/5/9 Richard Jones <rich at annexia.org>:
> On Sat, May 09, 2009 at 11:50:28AM +0100, James Courtier-Dutton wrote:
>> Some of them use more so called "hardware acceleration" such as Intel
>> VT or AMD-V.
>> It has been shown that using hardware acceleration can actually slow
>> some applications down when compared with software emulation,
>> particularly with the intel vt and amd-v hardware instructions.
>> Example applications are ones that use a lot of malloc/free calls.
>> intel-vt and amd-v can slow these applications down quite a lot.
>
> James, extraordinary claims such as this one require extraordinary
> proof, which I'm sure you'll be happy to provide.  I'm interested to
> know how exactly userspace library details like malloc/free are
> supposed to influence guest kernel performance.
>

It is not extraordinary. I could say "Go google the reason yourself"
.... but I like to help if I can.
This is not the article I read that made well supported claims
supporting my statements above, but it seems to at least support my
statement to some extent, in that hardware virtualisation instructions
are not always better than doing it in software.
http://developers.slashdot.org/article.pl?sid=06/08/12/2028223
The article I read actually made a much stronger case for software
visualization over hardware virtualization. For example, the whole way
the x86 architecture does memory management is messy at best. If you
want evidence for that statement, google "memory fragmentation"
The memeory management problems found in the x86 hardware can be
mitigated by using software that does it better, e.g. The Java VM.

When I attended the "kernel summit" a few years ago, there was a long
discussion about "memory pressure" and "memory fragmentation" and how
one might improve the situation in Linux, because Solaris was handing
it so much better.

Kind Regards

James
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