Re: [Xen-users] Xen Performance

Luke S Crawford
Tue, 02 Jun 2009 00:27:46 -0000

Michael David Crawford <mdc@prgmr.com> writes:
> Why do HVMs perform so poorly under Xen?  My experience so far is that
> they go at less then five percent of the speed they would on a
> physical machine.

Because without paravirtualized drivers, all I/O goes through what
is essentially quemu.  Slow.  Five percent seems a bit slow for that;
but the I/O degridation is pretty significant.

> A typical example of what I am experiencing is that with a single 2.5
> GHz Xeon vCPU and 512 MB of RAM, BeOS 5 Pro takes about fifteen
> minutes to boot to the desktop.

> But when installed directly on a 233 MHz Pentium II, getting to the
> desktop takes less than a minute.

There is weirdness with some other operating systems; sometimes they depend
on some hardware feature that is normally not in the critcal path so they
end up slow or not working at all.   For a while, FreeBSD had all kinds
of trouble running under HVM mode.  (It works fine these days, of course,
I/O is still slow. )

running xenoprofile would probably be enlightening, but I don''t know
if that is too much work, if it works fine under other virtualization systems.