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From: Blue Swirl <blauwirbel@gmail.com>
Date: Fri, 8 Jan 2010 18:04:02 +0000
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Subject: [Qemu-devel] Re: [PATCH] PPC: tell the guest about the time base
	frequency
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To: Alexander Graf <agraf@suse.de>
Cc: QEMU Developers <qemu-devel@nongnu.org>, Aurelien Jarno <aurelien@aurel32.net>

On Fri, Jan 8, 2010 at 5:43 PM, Alexander Graf <agraf@suse.de> wrote:
> Our guest systems need to know by how much the timebase increases every second,
> so there usually is a "timebase-frequency" property in the cpu leaf of the
> device tree.
>
> This property is missing in OpenBIOS, as is the "clock-frequency" property that
> tells the guest how fast the CPU is. FWIW that one is only used for
> /proc/cpuinfo though.
>
> With qemu, Linux's fallback timebase speed and qemu's internal timebase speed
> match up. With KVM, that is no longer true. The guest is running at the same
> timebase speed as the host.
>
> This leads to massive timing problems. On my test machine, a "sleep 2" takes
> about 14 seconds with KVM enabled.
>
> This patch exports the timebase and clock frequencies to OpenBIOS, so it can
> then put them into the device tree. I'll push the OpenBIOS change with the
> NewWorld patch set, once that's either been reviewed or applied.

IIRC copying the host CPU frequency to guest was rejected earlier for x86.