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List:       freebsd-emulation
Subject:    Re: FreeBSD/i386 guests using excessive host CPU
From:       Martin Simmons <martin () lispworks ! com>
Date:       2012-12-12 19:15:34
Message-ID: 201212121915.qBCJFYmg014095 () higson ! cam ! lispworks ! com
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>>>>> On Wed, 12 Dec 2012 12:43:36 +1100, Peter Jeremy said:
> 
> [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.

I can't repeat that with idle FreeBSD 8.0 guests running in VirtualBox 4.1.18
on Linux kernel 2.6.35.14-106.fc14.x86_64.  In fact, the 64-bit one uses 4.8%
of the CPU whereas the 32-bit one uses 4.2% (according to ps "bsdtime"
measured over 1000 seconds).

What absolute percentages are you seeing?

__Martin
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