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From: Robert Watson <rwatson@FreeBSD.org>
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To: Mike Silbersack <silby@silby.com>
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Cc: current@freebsd.org
Subject: Re: [patch] Auto-setting hz to 100 inside QEMU/VMWare
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On Fri, 28 Dec 2007, Mike Silbersack wrote:
> When running FreeBSD inside QEMU / VMWare, one of my pet peeves is that time
> is completely inaccurate. This seems to be cured by setting kern.hz=100
> (down from the default of 1000) in /boot/loader.conf, but I'm getting sick
> of doing that every time I set up a virtual box.
>
> So, here's a patch to have the kernel auto-detect that it's running inside
> one of those two environments and automatically make that adjustment.
>
> If you're running FreeBSD inside any other virtual environments (Parallels?
> Microsoft Virtual PC?) and can detect them via data in kenv, I'll be happy
> to add them to the patch as well.
>
> I have only tested this patch in QEMU so far, I will test inside VMWare
> tomorrow.
>
> If anyone could review and/or test this, it would be appreciated.
I like the general idea, but one thing that does worry me is that this
prevents me from using config to set HZ at all, I have to set it at runtime
using the tunable. Could we add an:
options VIRTUAL_HZ=100 # alternative default HZ to use with virtualization
Or something along these lines? kern.hz as a tunable could still override it,
but this would put the default in the config rather than in the code. So the
new logic would be something along the lines of
{
if (detect_virtualmachine())
hz = VIRTUAL_HZ; /* A big HZ hurts. */
else
hz = HZ;
}
I also wonder if detect_virtualmachine(), or whatever the most appropriate
name is, should be an MD routine shared by amd64, but also available on sun4v
in the form of int detect_virtualmachine(void) { return (1); }.
FYI, the vendor for Parallels is:
smbios.bios.vendor="Parallels Software International Inc."
In any case, having something along these lines in the tree would make my life
with Parallels and VMWare a lot easier "out of the box".
Robert N M Watson
Computer Laboratory
University of Cambridge