FreeBSD/i386 guests using excessive host CPU

[Peter Jeremy]

[Please copy me in any replies]

My VPS provider will not offer 32-bit FreeBSD guests because they use
excessive (ESXi) host CPU time.  I have done some experiments using
VirtualBox on my FreeBSD/amd64 8-stable host and see the same.

An idle 32-bit FreeBSD 9 or 10 guest uses very roughly 25% more host
CPU than an equivalent 64-bit guest.  An idle 32-bit FreeBSD 8 guest
uses very roughly 50% more host CPU than an equivalent 64-bit guest.

This problem does not show up with Linux or Windows7 but occurs with
both VirtualBox on AMD and ESXi on Intel CPUs.

Since the problem shows up with different virtualisation environments
and on different CPUs, this suggests this is a FreeBSD guest issue.
My suspicion is that the cost of handling an interrupt on FreeBSD/i386
is higher than the cost on amd64 - and this is more obvious on 8.x
because it doesn't use dynamic ticks.

Has anyone else seen this behaviour and does anyone have any suggestions 
for improving the FreeBSD/i386 performance.

-- 
Peter Jeremy
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 196 bytes
Desc: not available
URL: <http://lists.freebsd.org/pipermail/freebsd-emulation/attachments/20121212/3d483971/attachment.sig>