Re: [Xen-devel] [PATCH] xen: preserve native TSC speed during migration between identical hosts

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, May 24, 2017 at 04:25:05PM +0200, Olaf Hering wrote:
> After migrating a domU to another identical host a performance drop can
> be observed. One reason is that before migration TSC was accessed at
> native speed, after migration TSC has to be emulated. This happens
> because the measured CPU frequency is not accurate, the values differ
> even between reboots.
> 
> To avoid the emulation a tolerance range can be specified during boot
> with "vtsc-tolerance=N".  If the frequency expected by the domU is
> within the range, TSC access from the domU will remain native. If the

How can that be determined? As in how can the guest (domU) be within
the range? Is there some way to determine that? Is there some
matrix of the various OS-es that can tolerate this?

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